Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Schematics and Layouts => Topic started by: galaxiex on July 27, 2014, 10:06:34 PM

Title: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on July 27, 2014, 10:06:34 PM
Hello all, newb here... go easy on me  :) Here is a schematic I have generated after extensive searches failed to turn up anything usable.

I tediously/laboriously followed the board layout and made a drawing of all component placement and traces.
With that in hand I sat down and created the schematic in ExpressSCH. Took a couple tries but I think its good now.

Hoping someone can help with the crappy reverb sound I'm getting from this amp. Yeah, I know, it's a crappy little amp but I'd like to make it sound a bit better that it does right now. (Sentimental Value ya know?)

This amp actually has a pretty good deep sounding Tremolo tho the speed range is a bit narrow.

As you can see from the notes on the schem I have already made some changes as the amp was very quiet when I first got it.
Putting a jumper in place of R16 made the biggest difference in volume, but the already bad, tinny, feedback prone reverb got even worse.
I also replaced D2 with a new germanium diode that feeds the trem circuit and got a tiny increase in volume from that change as well.
I suspect the original diode was leaky.

I'm wondering if it's possible to replace the stock single spring piezo reverb tank with maybe the Belton Digi-Log module.

http://www.accutronicsreverb.com/ (http://www.accutronicsreverb.com/)

Might need to add a small driver/recovery board. I'm uncertain about what circuit would be needed to interface with the amp and where to tie in.
If you have looked at the schem you no doubt noticed the odd (at least to me) use of PNP transistors and the funky positive voltage on the chassis. Kinda weird compared to more modern designs.

I don't expect miracles but a bit more volume would be nice too.

Thanks for any and all reply's, help, advice, suggestions, ideas etc  :)

Edit: Oh ya, check the funky transformer phase splitter (at least I "think" that's what it is) to the "power amp" section.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: DrGonz78 on July 28, 2014, 05:55:29 AM
Not sure this will help that much but I figured it would be interesting to post checkmate 66 schematic. Sorry the quality of the file is not perfect by any means but it shows an example of a solid state amp, hopefully similar to your amp.

Edit: Actually looking closer this looks to be very close if not exactly like your output. Examine how they have the 2.2, 1.8k and 33 ohm resistors in place in this schematic. Try to do the same in your layout and I think you find that this is what you have there in your checkmate 21.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on July 28, 2014, 10:12:59 AM
Welcome galaxiex.


The application of the tremolo directly to the input via D2 is ... um  ... shall we say "unique".

Which draws attention to the amp's input impedance, or lack of it.  I make it about 40k ohms which must be the lowest I've ever seen, and would tend to make the guitar sound dull and lifeless.  Add a buffer, or always use a pedal (without true bypass).


Quote from: galaxiex
Tremolo tho the speed range is a bit narrow.

This is the classic problem with all Phase Shift Oscillators that only vary one of the tuning components - lack of range.


Quote from: galaxiex
I suspect the original diode was leaky.

All germanium semiconductors are born like that.


Quote from: galaxiex
If you have looked at the schem you no doubt noticed the odd (at least to me) use of PNP transistors and the funky positive voltage on the chassis. Kinda weird compared to more modern designs.

Yes, but there was a time when this was very common with Asian builds, late 60's/early 70's era.

The single driver transformer arrangement is also very in keeping with the thinking of that time - DrGonz's circuit is a classic of the type.


Quote from: galaxiex
I'm wondering if it's possible to replace the stock single spring piezo reverb tank with maybe the Belton Digi-Log module.

It's possible, but note that it requires a supply of 5V @ 100mA, so you will require a regulator or some other power supply for it.


Quote from: galaxiex
a bit more volume would be nice

About the only thing you can do is to fit a more efficient (dB/W) speaker.


But I have to agree with JM.  This amp isn't just old, it was a dated design when it was built, and to be brutally honest it would have been built down to the very last cent.  Teisco's corner of the market was cheapest of the cheap.  Not badly built for what they are, it's just that they aren't much.  It may be a classic now but it was only a throw-away item back then, not much better than a toy.

Even if you kiss this frog, it's still going to be a frog I'm afraid.
(http://images.nationalgeographic.com/wpf/media-live/photos/000/004/cache/amazon-horned-frog_443_600x450.jpg)

If you're really that keen to hot-rod a small amp, then build one of the many chip-amp based designs, and go from there; better prospects I think.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on July 28, 2014, 10:13:42 PM
Much Thanks to everyone for your replies. :)

I will try to address them in order.

JM Fahey;

“1) the driver transformer is improperly drawn, it needs a primary winding and 2 independent secondary ones.”

Yes, I see now my error in drawing it like I did.
My not knowing how the six pins on the transformer are wired internally, I simply assumed each side of 3 pins were simply a coil with center tap.
I understand now how that is wrong, and I will redraw the schematic to correct this.

“2) the supply shows a 1K resistor in series with *everything*”

Yes… that IS how it’s wired.
I thought it very odd so I shorted the 1K and the amp did not work properly. I don’t now recall exactly what happened, but I think the Trem quit working when that 1K was shorted, so I put it back to original.

“3) the tremolo diode can't be wired that way”

Respectfully, it is indeed wired that way. I checked the traces on the board and the components connected to them at least a dozen times or more. Probably more…..
It really is wired like that. I can’t explain it. The Trem does work.
Perhaps later I will upload a video demo so you can hear how amazingly effective the Trem actually is. Aside from the narrow speed range it works great. Very deep throb. The only other Trem issue is the Intensity control needs some “expansion” of the range. It goes from full OFF to almost Maximum Intensity with about a quarter turn of the knob.

Pics will be posted of the “piezo” reverb tank.

As you can see, this is a Head type amp. I didn’t get a speaker cab with it, but the original was likely a 2X8 to make this a “Mini Stack”

For now I am using a Vintage @ 1974 Traynor GuitarMate 12” speaker cab. I unplugged the GuitarMate amp and made a cable to use just the speaker.

I will explain here that my interest in this amp is because I had the Sears Silvertone version when I was about 13 years old. Mine was exactly the same as this Teisco but for a silver front panel and the Sears name on it. I had the 2X8 speaker cab too. The Head and cab have these little suitcase type latches to clip the head to the top of the cab. I looked hard to find the Silvertone version with no luck, and when this Teisco came up on eBay I grabbed it.  :)

I’ll see if I can find some pics. There are other versions of this amp out there.

I plan to build a 2X8 speaker cab for it as similar to the original as possible based on pics I have found of similar amps. I even ordered some of those suitcase latches to clip the head on top.  :) I’ve built speaker cabs before so that won’t really be a problem.


DrGonz 78

Thank you for the schematic.  :) I will use it to redraw the output stage. I’m sure that is how it should be.

Roly

Yep, the Trem thru D2 is "unique"  :)

Input impedance;
I measured 18.75K directly on the first guitar input jack using my Fluke meter.
All other amps I have checked like this measure 1meg or more, so ya, it’s gotta be loading down the guitar. Perhaps a small buffer stage could be placed on the input… or… just always use a pedal… hmmm….

Trem lack of range… I’ll live with it, as I said above it works ok to suit me.

D2 diode leaky;
The original diode forward voltage drop is 2.43 and the replacement measures 3.70 with my meter on diode check. Don't know if the low V drop is an indication of "leaky" but the higher drop diode made the amp louder. I tried a silicon diode but then the Trem quit working.

Reverb;
I can cobble up a 5V reg to power the reverb brick, but I’m uncertain where and how to interface with the amp. Reverb drive and recovery amps needed? I don’t know… Will do more research into this (and get a brick ordered so I have something to play with). Any help along these lines will be much appreciated.  :)

I’ve been researching efficient 8” speakers and the Celestion 8-15 looks ok at 95dB but if you have any suggestions I’m open.

Yep, it’s a dated design and not really much better than a toy, but I like it, Frog warts and all. I certainly won’t gig with it but might use it as a “novelty” sound for our jam/practice place.  :)

Thank again for all your input, it is much appreciated.  :)

Hmmm having trouble getting the pics to post... bear with me...

Ahh... ok... got it.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on July 29, 2014, 08:26:20 AM
Way cool factor amp  :tu:

If at all possible, post a couple close ups of the reverb transducers, from different angles.
Can't even imagine how it works, but never saw anything like that.
Do they have any magnets inside?
Thanks.

Thanks!  :) I do think its kinda cool myself. 8)

Sure I'll get more pics of the tank later. Magnets? I'm not sure...
I "think" only piezo crystals... I'll test by placing a tiny metal bit next to each transducer.

Right now i am in the process of re-drawing the schem.
WOW I found more mistakes than I first thought...  ::)  :duh
I musta been real tired and more than a little cross-eyed from squinting at tiny traces and parts.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on July 29, 2014, 01:40:08 PM
Something like a TL071 voltage-follower right at the input J1 would give you as much input impedance and you need.  Me, I'd kludge it up on a small bit of stripboard and mount it on stiff wires directly on the socket, bring power down to it.


The D2 results are odd.   You should get around "100"mV for a germanium forward on a DMM diode test, and the PIV should be at least 20V and more like 50V, so I donunnerstan.  Could be leaky or normal, hard to say with silicon-oriented instruments.


Main thing I'd do with the reverb module is put a 5V zener clamp across the in and output (or similar) to make sure it is not subjected to voltage outside its pay grade.

I suspect that with an active module like this you will be looking for attenuation rather than gain once you try it, but even needing a transistor or op-amp is no big deal.

Interestingly that springline drive looks like it is side-to-side rather than the twist that Belton use.


95dB ain't so hot.  For a small amp like this I'd be shopping around 100dB/W, or better if you can find it - every dB really counts when you're short of watts - and maybe a bigger diameter if it presents.


R9 and R10 are already attempts to fix the abrupt Depth control action.


Quote from: galaxiex
I certainly won’t gig with it

Might be time for OneBaldBob's story about using a micro amp into a PA mike, hidden behind a cold Marshall stack at a big concert.   :lmao:


3-core mains lead, earth very secure to the chassis, out with that "death cap"  :trouble  on the mains infeed (which I note you have already disconnected  :dbtu:).
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on July 29, 2014, 02:29:17 PM
Thanks much for your help Roly.  :)

Your suggestion for the buffer is close to what I was thinking,
cept I was more on the lines of possibly a super simple single fet and a couple R's and cap on a small perf board.
I'll look at the TL071 too.

I should mention here that I have NO formal education in electronics, only what I have gleaned from messing around and reading Forrest Mims books, Data sheets, and app notes... and not that I always understood what I was reading....  ;)

Ya, I don't get the D2 results but it seems to work so I'll let it be.  ;)

For the reverb I was pondering a zener or even a little 3 leg regulator but the zener sounds easier.
I ordered the Reverb Brick so while waiting for that I'll mess with the input buffer.

Here's more pics of the piezo tank.

For the speaker I'm having trouble finding an 8" with 100dB or better... I think I could go to a pair of 10's in the cab I plan to build.
Looks like that Sorrento has 10's in it so they will probably fit.
Considering the output stage, any suggestions on ohms and series or parallel?
I don't know what the original speakers were.. 4 ohm, 8 ohm or what...

I suspected R9 and R10 were attempts to fix that, as they are mounted on the pot. It's ok, just need to set the depth "carefully".  ::)  ;)

Heh! Micro amp to a PA, I shudda thought of that!  8) <3) :dbtu:

Death cap unhook was first thing I did so I did learn sumpthin from reading after all.  ;)

3 wire cord is in the plans but I was unsure how that works with the Pos voltage on the chassis????

Here's some more pics of the reverb tank for J M Fahey , sorry, that's as close as my camera will go, and a schem I copied of a Checkmate 10.
Looks like the same output stage as the CM-21, still working on putting that in my CM-21 schem.
Note the 10V and 13V annotations on the CM-10 schem, they were there already, I just copied it like I saw it.
Odd they didn't put a minus sign on them.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on July 30, 2014, 01:09:54 AM
Ok, here is the redrawn schematic for the Teisco 21.

Hopefully no errors this time.

I did a complete new layout rather than try to fix the first one.

I hope this is easier to read.  :)

Arrrgh! I missed a couple of values and part #'s I must be getting tired...

Ok, here it is again... last one for tonight.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on July 30, 2014, 05:44:27 AM
Much easier to follow.

Earth missing on Intensity pot.   {doncha just hate that?}


"All non-trival programmes have bugs."  Programmers truism.

"All non-trivial circuits have mistakes."  Tech's truism.

Once upon a time in Ye Olde Days of Yore I was building industrial safety systems.  One such (thankfully not of my design) went through prototype testing, company validation, then validation by a government department, and into production before the massive and potentially tragic blooper was spotted.

If there is one thing that a tech must always be, it's suspicious; is my meter fooling me, is that a circuit drafting error, is that solder joint really as good as it looks at a distance?  {is the client telling me the truth about how the amp blew up?}

"Just concentrate on the facts Watson."    8|



Circuit Drafting Muse

After you have looked at a lot of guitar amp circuits there emerges a bit of a very loose convention about how the circuit is laid out.

Input starts top left and runs across to the output stage top right.  The power supply is bottom right just above the title block, and the tremolo and reverb are placed bottom left.  Very generally.

I note that you have already done some of this re-laying out in your rev1 (and thanks for the rev no., I use the date in reverse as a meaningful date/serial yymmdd  140730 appended to drawings, file names &c.  You leave a developmental history trail that can be reviewed if an errors has crept in, and you always know which is the latest.)  I like the ground at the bottom, even if the supply rail happens to be negative in this case (but this should be clearly marked because it's not what most techs would assume these days).

Naturally you have to be driven by the task at hand, so if it has a particularly complicated preamp you might set the first part of the preamp across the top of the sheet, the rest of the preamp and the main amp across the middle, so the signal path is "backwards-S" shaped.

Similarly there are sub-conventions for drawing different stages/functions so that they are instantly recognisable.  The Phase Shift Oscillator for example is typically drawn;

(http://www.electronics-tutorials.ws/oscillator/osc20.gif)

This highlights the Phase Shift Network and instantly identifies it as an oscillator stage, and of what type.

It is quite possible to draft a circuit where it is very hard to work out the various signal and power flows, what each stage does, and how it does it (just as spin doctors can use real words to obscure what they are actually saying, "the aircraft suffered a systems malfunction" i.e. an engine dropped off.)

The primary object of a circuit, or any technical drawing really, is to communicate to other techs down the track, and to do so quickly and effectively, and that must always remain your number one goal.  There is no law against drafting an awful circuit, you will just be cursed to the seventh son of the seventh son by every tech who sees it.  So every circuit is a bit of an artwork, and some elegance is required in its functionality.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: g1 on July 30, 2014, 11:26:42 AM
3 wire cord is in the plans but I was unsure how that works with the Pos voltage on the chassis????
  There is no voltage on the chassis.  It is positive ground.  The supply is negative instead of positive.  Many old cars used to be positive ground.
  Voltage and ground can be tough to wrap your head around, all voltage is relative to something, we usually use ground as that reference, but it is not necessarily so.
  In this case, everything is in reference to the positive, so we call that ground, and you will be connecting that point to the chassis.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on July 30, 2014, 12:23:48 PM
Much easier to follow.

Earth missing on Intensity pot.   {doncha just hate that?}


"All non-trival programmes have bugs."  Programmers truism.

"All non-trivial circuits have mistakes."  Tech's truism.

Once upon a time in Ye Olde Days of Yore I was building industrial safety systems.  One such (thankfully not of my design) went through prototype testing, company validation, then validation by a government department, and into production before the massive and potentially tragic blooper was spotted.

If there is one thing that a tech must always be, it's suspicious; is my meter fooling me, is that a circuit drafting error, is that solder joint really as good as it looks at a distance?  {is the client telling me the truth about how the amp blew up?}

"Just concentrate on the facts Watson."    8|



Earth missing....    :o   ahhh knew it was too good to be true..  ;)

I work as a automatic transmission re-builder and the hardest thing to do is trouble shoot something that someone else rebuilt/messed up.

"Objects are not always as they appear"


Circuit Drafting Muse

After you have looked at a lot of guitar amp circuits there emerges a bit of a very loose convention about how the circuit is laid out.

Input starts top left and runs across to the output stage top right.  The power supply is bottom right just above the title block, and the tremolo and reverb are placed bottom left.  Very generally.

I note that you have already done some of this re-laying out in your rev1 (and thanks for the rev no., I use the date in reverse as a meaningful date/serial yymmdd  140730 appended to drawings, file names &c.  You leave a developmental history trail that can be reviewed if an errors has crept in, and you always know which is the latest.)  I like the ground at the bottom, even if the supply rail happens to be negative in this case (but this should be clearly marked because it's not what most techs would assume these days).

Naturally you have to be driven by the task at hand, so if it has a particularly complicated preamp you might set the first part of the preamp across the top of the sheet, the rest of the preamp and the main amp across the middle, so the signal path is "backwards-S" shaped.

Similarly there are sub-conventions for drawing different stages/functions so that they are instantly recognisable.  The Phase Shift Oscillator for example is typically drawn;

(http://www.electronics-tutorials.ws/oscillator/osc20.gif)

This highlights the Phase Shift Network and instantly identifies it as an oscillator stage, and of what type.

It is quite possible to draft a circuit where it is very hard to work out the various signal and power flows, what each stage does, and how it does it (just as spin doctors can use real words to obscure what they are actually saying, "the aircraft suffered a systems malfunction" i.e. an engine dropped off.)

The primary object of a circuit, or any technical drawing really, is to communicate to other techs down the track, and to do so quickly and effectively, and that must always remain your number one goal.  There is no law against drafting an awful circuit, you will just be cursed to the seventh son of the seventh son by every tech who sees it.  So every circuit is a bit of an artwork, and some elegance is required in its functionality.

Thanks for your insights and explanation of this.  :)

I may at some point redraw (ver2) the schem along those lines. I like the yymmdd. Very clever. I may borrow that for future versions.

btw, that first schem, is my first one! I have never drawn a schem before that... although I've looked at lots of them.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on July 30, 2014, 12:28:29 PM
3 wire cord is in the plans but I was unsure how that works with the Pos voltage on the chassis????
  There is no voltage on the chassis.  It is positive ground.  The supply is negative instead of positive.  Many old cars used to be positive ground.
  Voltage and ground can be tough to wrap your head around, all voltage is relative to something, we usually use ground as that reference, but it is not necessarily so.
  In this case, everything is in reference to the positive, so we call that ground, and you will be connecting that point to the chassis.

Thank you!

I thought that was so, and of course thinking about it now it only makes sense. Being in the automotive repair business, I of course, know about "positive earth" cars but have never worked on or dealt with them.

Earth is relative....   :lmao:
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on July 30, 2014, 10:06:38 PM
This might seem stupid... the "positive earth" thing has me stumped again.

I'm trying to make a input buffer using a TL071.
I get that the chassis is at positive potential and I hook that to pin 7 of the TL071.
Pin 4 goes to "negative" on the board somewhere, probably after the 1K resistor R37.
Pin 6 to 10uF cap to guitar input on the amp.
Guitar in to .1 cap to pin 3.

So where do my "signal grounds" go?

Here is the circuit I am trying to use.
This can't be that hard but I can't wrap my head around it.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: g1 on July 30, 2014, 11:00:20 PM
  The point marked +9 goes to ground.  The points marked with ground symbol go to your negative supply voltage.  The TL071 should be able to handle up to 36V difference between pins 4 and 7 so you should be fine.
As you see, pin7 will still end up being "positive" in relation to pin 4.
Pin3 still ends up being at half the supply voltage (due to R1/R2 voltage divider).
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on July 30, 2014, 11:54:59 PM
Thanks! I'll try it. If I blow something up, well... it's a 70 cent IC. I bought a bag of 10.  :)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on July 31, 2014, 12:39:25 AM
Ok I got the buffer to work. Turns out I had an open 10uF cap. (old stock in my junk) No signal getting thru.

But now the trem doesn't work! Rats! That is the one feature I like about this amp.

Seems like that goofy diode driven trem circuit wants to see some sort of load? on the input side.
As a test I removed the buffer and just plugged the guitar in.
Trem works.
Leave vol up and unplug guitar.
Should still "hear" the trem throb with all the background hiss.
No dice, the trem quits when you unplug the guitar. Weird.

Anyone got ideas how to make the trem work with the buffer installed?

BTW with the buffer installed the amp does sound a LOT better and slightly louder too.
Now to get the trem working again...
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on July 31, 2014, 09:52:30 AM
Quote from: galaxiex
I work as a automatic transmission re-builder and the hardest thing to do is trouble shoot something that someone else rebuilt/messed up.

We had a rule that whoever took it apart had to put it back together.  This could get complex if a couple of other techs had been called in to investigate something.


Well your signal grounds go to ground,  The fact that this happens to be positive and the supply rail is -20V is immaterial.

I'll explain.

Signal is an AC entity, and as such it sails blissfully straight through the DC barrier of your input DC-isolating/AC-coupling cap.  So it doesn't actually matter what DC voltage your source is sitting at because it is blocked by C1.

Consider a simple preamp stage.  As the signal goes up and down so the current through the stage goes up and down.  This same changing current must also be being drawn through the power supply lines, and if there is any series resistance (and there always is) then this will cause the voltage on the supply line to have the stage signal imposed on it - it will flap up and down too.

Other stages that are on the same supply will experience this as either negative, or positive, feedback (and low frequency "motorboating" often results from a supply line bypass cap failing low or open).

So we 'by-pass" the supply lines to each other, generally using a large value electro cap.  This effectively short-circuits the two DC supply rails together for AC signals, so for AC signal considerations both actual ground and the supply rail(s) are effectively "ground".

Now, while we are here, take a 0.01uF to 0.1uF disk ceramic or poly and connect it "VHF style" with the shortest practicable leads directly to the +ve and -ve supply pins of the TL071.  Op-amps in general and multi's in particular should have a good HF bypass right on their +/-supply pins for best results.

Personally I'd bump the bias resistors up to 2.2Megs each to get 1Meg Zin, and I'd stick a couple of 1N914 or similar diodes reversed biased across each resistor, and a 10k somewhere in series with C1 for some protection.

Coming together.   :tu:


P.S.
Quote from: galaxiex
Anyone got ideas how to make the trem work with the buffer installed?

I'm on the case.   :trouble


edit: typo
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on July 31, 2014, 12:03:52 PM
Quote from: galaxiex
I work as a automatic transmission re-builder and the hardest thing to do is trouble shoot something that someone else rebuilt/messed up.

We had a rule that whoever took it apart had to put it back together.  This could get complex if a couple of other techs had been called in to investigate something.


Well your signal grounds go to ground,  The fact that this happens to be positive and the supply rail is -20V is immaterial.

I'll explain.

Signal is an AC entity, and as such it sails blissfully straight through the DC barrier of your input DC-isolating/AC-coupling cap.  So it doesn't actually matter what DC voltage your source is sitting at because it is blocked by C1.

Consider a simple preamp stage.  As the signal goes up and down so the current through the stage goes up and down.  This same changing current must also be being drawn through the power supply lines, and if there is any series resistance (and there always is) then this will cause the voltage on the supply line to have the stage signal imposed on it - it will flap up and down too.

Other stage that are on the same supply will experience this as either negative, or positive, feedback (and low frequency "motorboating" often results from a supply line bypass cap failing low or open).

So we 'by-pass" the supply lines to each other, generally using a large value electro cap.  This effectively short-circuits the two DC supply rails together for AC signals, so for AC signal considerations both actual ground and the supply rail(s) are effectively "ground".

Now, while we are here, take a 0.01uF to 0.1uF disk ceramic or poly and connect it "VHF style" with the shortest practicable leads directly to the +ve and -ve supply pins of the TL071.  Op-amps in general and multi's in particular should have a good HF bypass right on their +/-supply pins for best results.

Personally I'd bump the bias resistors up to 2.2Megs each to get 1Meg Zin, and I'd stick a couple of 1N914 or similar diodes reversed biased across each resistor, and a 10k somewhere in series with C1 for some protection.

Coming together.   :tu:


P.S.
Quote from: galaxiex
Anyone got ideas how to make the trem work with the buffer installed?

I'm on the case.   :trouble

You Sir, are just AWESOME!  :dbtu:

Thank you so much for the easy to understand explanation! I love it!  <3)

In all the time I have been messing with electronics and reading tech books and whatnot,
I have never really "got" the supply/signal relationship and the need for bypass caps etc. (I just knew circuits needed em cuz the book said so)

I just now did, (Big light bulb emoticon) Thank You!!!!

PS. 10K in series on the opamp side or guitar side? Or does it matter? I'm guessing guitar side.

Also, I got lots of 1N914's, no problem. I even understand reverse bias.  :cheesy:
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on July 31, 2014, 03:05:07 PM
My pleasure.   :)

.
A 10k (or so) goes between the external input socket and the op-amp input pin.  It and the cap are in series so it doesn't matter which is first.

When you have diode clamps you also have to have some series resistance or the diodes could be overwhelmed by what could possibly come up the front end (e.g. accidentally hooking the output of another amp to the input of this one, has been known to happen in the rush of setting up; walk across a carpet and pick up a few kV of static charge, then touch the end of your guitar lead before you plug it in).  The resistor limits the current flow, and it's the current that does the damage.

Since it's a -ve supply rail these clamp diodes go across the input with their cathodes pointing towards the +ve/ground end so they are normally off.  If the input voltage tries to go outside the supply bounds these diode clamp it.

.
Now looking at your op-amp-killed-the-radio-star problem.

Because the input bias resistors on the op-amp bias the input to about -10V, and because it is a 100% feedback voltage-follower, the op-amp output will also be at -10V.

When it is first turned on the output cap C2 10uF will be discharged, so when the op-amp output drives it to -10V the other side, the input/trem/diode side, will also go to -10V and present that to the amp input.  This totally bogs up the critical biasing of the trem diode and kills its action by reverse biasing it by -10V.  Signals go past just fine, they just don't get modulated by the diode which is cut off hard.

Eventually the cap will charge up via the diode leakage (cos there is no other path), the input voltage will fall to something reasonable, maybe minutes to millivolts, and the trem should start working again.  But 10uF charging at microamps will take forever (and maybe never if the cap leakage discharging the cap is larger than the diode leakage charging it.  It may end up floating about at a few volts, depending on the temperature and general mood, and never fully charge back to zero volts).

The simple answer is to provide a (better) charging path.  The impedance at this point is already obnoxious, and the buffer makes it unimportant anyway, so we can't do a lot to offend it.

If you add a ~100k resistor across the (old) input, that is from the end of C2 not connected to the op-amp output, to ground, it should charge C2 and settle to around zero in about 2-3 seconds after switch on.  This cap should have its -ve end to the op-amp output and +ve end towards the trem diode.

.
I would expect it to be slightly louder and a bit more lively with the guitar isolated from the previous loading effect of the low-Z input.

.
This trem BTW only modulates downwards on peaks about 20-30% of the time leaving the signal full and unmodulated for 80-70% of the time.  Most modulations systems provide 100% sine variation over the entire LFO cycle, so this will sound different.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on July 31, 2014, 05:31:48 PM
My pleasure.   :)

.
A 10k (or so) goes between the external input socket and the op-amp input pin.  It and the cap are in series so it doesn't matter which is first.

When you have diode clamps you also have to have some series resistance or the diodes could be overwhelmed by what could possibly come up the front end (e.g. accidentally hooking the output of another amp to the input of this one, has been known to happen in the rush of setting up; walk across a carpet and pick up a few kV of static charge, then touch the end of your guitar lead before you plug it in).  The resistor limits the current flow, and it's the current that does the damage.

Since it's a -ve supply rail these clamp diodes go across the input with their cathodes pointing towards the +ve/ground end so they are normally off.  If the input voltage tries to go outside the supply bounds these diode clamp it.

.
Now looking at your op-amp-killed-the-radio-star problem.

Because the input bias resistors on the op-amp bias the input to about -10V, and because it is a 100% feedback voltage-follower, the op-amp output will also be at -10V.

When it is first turned on the output cap C2 10uF will be discharged, so when the op-amp output drives it to -10V the other side, the input/trem/diode side, will also go to -10V and present that to the amp input.  This totally bogs up the critical biasing of the trem diode and kills its action by reverse biasing it by -10V.  Signals go past just fine, they just don't get modulated by the diode which is cut off hard.

Eventually the cap will charge up via the diode leakage (cos there is no other path), the input voltage will fall to something reasonable, maybe minutes to millivolts, and the trem should start working again.  But 10uF charging at microamps will take forever (and maybe never if the cap leakage discharging the cap is larger than the diode leakage charging it.  It may end up floating about at a few volts, depending on the temperature and general mood, and never fully charge back to zero volts).

The simple answer is to provide a (better) charging path.  The impedance at this point is already obnoxious, and the buffer makes it unimportant anyway, so we can't do a lot to offend it.

If you add a ~100k resistor across the (old) input, that is from the end of C2 not connected to the op-amp output, to ground, it should charge C2 and settle to around zero in about 2-3 seconds after switch on.  This cap should have its -ve end to the op-amp output and +ve end towards the trem diode.

.
I would expect it to be slightly louder and a bit more lively with the guitar isolated from the previous loading effect of the low-Z input.

.
This trem BTW only modulates downwards on peaks about 20-30% of the time leaving the signal full and unmodulated for 80-70% of the time.  Most modulations systems provide 100% sine variation over the entire LFO cycle, so this will sound different.

Wow, I even understood all that too.  ;) I can't wait to get home from work to try it!  :) :) :)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 01, 2014, 12:06:14 PM
Sorry for the delayed reply...

The trem works!  :) With the buffer!  :) The 100K did the trick.  :)

More later... I'm at work right now...
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 01, 2014, 04:17:07 PM
Cool.  That's what we like to hear.   :dbtu:
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 03, 2014, 02:34:22 AM
This amp now sounds fantastic!?!?!  :loco

Well.. not really... but it sounds waaay better than when I first plugged it in.  :)

Thanks again Roly for all your help. I really appreciate it. I hope I will be able to give back to this forum someday.
Thanks to all others that contributed as well.

Here's some pics of the buffer and installation.

Yes, I know, I still haven't added a 3 wire grounded power cord yet. Gotta do that next.

As you can see I took your suggestion to use a small strip board and mount it on stiff wires.

I also added connectors to make board removal easier. (I have no doubt I will be working on it more)
The amp is amazingly quiet even with the rats nest of wires and general lack of shielding.

It still lacks volume but a more efficient speaker will help.
However... the most efficient speaker I could find is a 10 inch Eminence Red Fang at 102.1 dB but it's approx $200.00 Canadian!!!!
And I need 2 of them if I build a "replica" speaker cab.

If anyone has any suggestions for a reasonably priced 10 inch guitar speaker of 100 dB efficiency or better please let me know.

Cheers for now!
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 03, 2014, 08:13:30 AM
All very neat.

Quote from: galaxiex
I still haven't added a 3 wire grounded power cord yet.

You do that FIRST goddamit!   :trouble

(http://emoticoner.com/files/emoticons/smileys/electric-smiley.gif?1292867589)

Just leaving aside your worthless hide for a moment, tender little IC's like TL071's don't like floating about at roughly half your mains voltage.  Even if it is current limited enough so you don't get electroluxed, the op-amp input's won't take too kindly to such excessive voltage.

"Excessive voltage?  I don't feel no excessive voltage"

Well no, you may not, or it may just seem that the chassis is vibrating at mains frequency when you touch it lightly.  Well it isn't vibrating, you are, due to leakage current.

A mains transformer is very well insulated against resistive leakage between windings, but having some capacitive coupling, and therefore some leakage current, is unavoidable.

One side of the mains is connected to actual ground, the neutral, while the other side is the active.  Now since one side is grounded this is an unbalanced signal to ground and the effect of the stray capacitive coupling between the windings is to create a capacitive divider between active and neutral/ground, meaning that without grounding everything connected to the secondary winding will float at about half mains voltage.  If you touch your neon screwdriver to the chassis it should light up dimly (and these are a literal life-saver, a must have, and a must use).

The capacitance may be quite small, so the amount of current that can flow at mains frequencies will also be very small, but without a ground there is nothing to limit the voltage, to harmlessly sink this leakage current.

Now you are standing on ground and you touch the input to the op-amp, but the whole of the amp circuit is going up and down half mains voltage, so from the point of view of the op-amp FET input you have just applied half mains voltage to it, and it won't like that at all.

That little green wire is your last line of defence against your IC's (or indeed yourself) being unexpectedly blasted into the hereafter, so take it very seriously indeed.  If you are going to check and correct the mains wiring at any time, always do it first.   :dbtu:
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 03, 2014, 09:57:28 AM
SIR! YES SIR!!!!

Seriously, I had no idea... which I realize shows my lack of knowledge/understanding in this area.

I mean, I know grounds are important, but once again, your clear simple language puts a new perspective/understanding on the subject.

I guess we (the uninformed/unaware) become complacent since we see so many 2 wire appliances that apparently "don't need a ground".
Then too there are the 2 wire power tools (Drills especially) that have the label "Double insulated" ...
...and maybe we think it has something to do with the cold....  :lmao:

Ok, not really a laughing matter since you could be killed,
but I am old enough to have lived in an age where almost everything only had a non-polarized 2 wire plug.
I'm NOT old enough to have seen houses that were wired with 2 BARE wires and NO ground, running thru the walls and terminated at glass insulators.
But I've obviously heard of them...

Anyway, point taken. Understanding received. The amp will not be plugged in again until said 3 wire is installed.

Once again, Thank you!  :)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Bakeacake08 on August 03, 2014, 12:32:56 PM
Wikipedia has a concise explanation on grounding classes that made a lot of sense to me when I was learning about grounding techniques.

http://en.wikipedia.org/wiki/Appliance_classes
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 04, 2014, 12:26:58 AM
Wikipedia has a concise explanation on grounding classes that made a lot of sense to me when I was learning about grounding techniques.

http://en.wikipedia.org/wiki/Appliance_classes

Bakeacake08 thanks for that link. Very concise and makes sense.
Thanks for contributing to my understanding of this.  :)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 04, 2014, 11:08:25 AM
Quote from: galaxiex
Seriously, I had no idea...

And that is what we are here for. 

"Double insulated" instead of a safety earth seems to have worked out in practice but I'm not a great fan because I've been inside many items where a manufacturer's idea of "insulated" doesn't really coincide with mine.

Let me give you another sobering thought.  The strings on your guitar are deliberately connected back to the ground/screen side of the guitar electronics.  Via the guitar lead this is connected back to the amplifier chassis.  So if it goes live, so do you!

More common and annoying is when you are singing as well as playing, and while floating leakage may only be a very small and harmless current it can bite your wet lips if you happen to touch the mike on a properly grounded PA system.  Not dangerous, but definitely off-putting.  Nibble and tingles are warning signs that something isn't right and needs speedy attention.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 04, 2014, 11:50:24 AM
Yep, I have been reading the safety pages on your website Oz Valve Amps and saw that bit about the guitar strings.
Sobering indeed. And ya, I've had that microphone "tingle" before and knew it was a ground issue.
We used to reverse one of the 2 wire cords in the outlet (usually the guitar amp) to make it stop.
Now of course most modern stuff is 3 wire and the tingle should not happen but of course there can be mis-wired mains and other faults that still have this come up from time to time.

Ok, so back to this amp...

I want to have all 3 inputs functional.

Can I use the 1 buffer for all 3 or is there a need to make 2 more buffer boards?

As an option I'm supposing I could make one of the buffer boards have a little gain, so 1 input could be "High Gain" ???

Thoughts?

Edit; Further thought perhaps 1 high gain input, 1 "Normal" buffered input and 1 stock original low Z input.

I would number them L > R

1. Normal
2. High
3. Low

The Low-Z input would be pretty useless for the most part... but allows a quick easy way to compare from original to the others.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 05, 2014, 12:22:26 PM
In Australia, which has always had three-wire "Live-Earth-Neutral" practice, mike "tings" should never happen at all, but particularly at venues it is not uncommon to encounter amateur wired extension leads and power points with Active-Neutral transposed, or no earth at all.

First time the venue operator gets told, but a couple of times after a second gig the supply authority got told (these days it would be WorkSafe).  Most venue operators are responsible about providing a safe workplace for musicians and will make it good, but the few who aren't deserve an official ferret up their trouser leg.  {I spent years in industrial safety gear so I'm rather hard-nosed about irresponsible management.}


How about;

In1 -> gain op-amp -> In2 (switch socket) -> buffer -> In3 (switch socket) -> old input.

With nothing in In3 it connects the old input to the buffer output.
With nothing in In2 it connects the buffer input to the gain op-amp output.
{you don't need a drawing do you?}

Actually a lot of amps have a Low-Z input available on one of the sockets, generally the insensitive one, which is effectively a Line level input for playback input from tape, CD, Pod, laptop, whatever.  This can be handy at "weddings parties anything" where the band is the whole show and has to also provide playback music between sets (and PA for drunken speeches etc  ::) ).
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 05, 2014, 05:03:29 PM

{you don't need a drawing do you?}



ummmm, I want to say yes... but that's just my mind being lazy.... gimme a day or 2 to figger it out myself.  :tu:

Got other stuff going on right now. This amp is not my whole life...  ;)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 06, 2014, 12:58:27 AM
Well, that didn't take as long as I thought it would....  ;D

No doubt it might need some tweaking but I think I got the general idea...

Whatcha think?  :)

Note; I did not draw this with respect to the positive chassis/negative supply.
I'll figger that out later. It was just easier for me to mash this up quick using normal supply polarity.
I know too the polarized caps will need switching around for the actual install.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 06, 2014, 11:57:18 AM
Quote from: galaxiex
Whatcha think?  :)

Looks like you've got that down.   :dbtu:

ExpressSCH doesn't have much in the way of jack socket symbols so I assume you are thinking sockets that have a single N.C. contact to the hot.  I'd only suggest that you use the same for the gain J1 and run that contact to ground as is normally done to quiet the channel.

It's possible that your added front end gain may overwhelm the tremolo when you use J1, but we'll see.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 06, 2014, 02:31:46 PM
Quote from: galaxiex
Whatcha think?  :)

Looks like you've got that down.   :dbtu:

Thanks!  :)

ExpressSCH doesn't have much in the way of jack socket symbols so I assume you are thinking sockets that have a single N.C. contact to the hot.  I'd only suggest that you use the same for the gain J1 and run that contact to ground as is normally done to quiet the channel.

ExpressSCH came with the switching jacks you see in the schem.

I "made" the single open jack in ExpressSCH, (here in Canada we call them jacks, not sockets, at least I do...  ;) ),
...but I see now that J1 should have a contact to ground to quiet the input with nothing plugged in.

It's possible that your added front end gain may overwhelm the tremolo when you use J1, but we'll see.

Ya, I was wondering about that, and possibly overloading the first amp stage as well.
That gain stage I just copied from the web, said it has a gain of 3.2.
I didn't calculate it, not that it's hard, it was late and I just got er dun quick like.

I can already overwhelm the trem by playing/strumming hard, it kinda fades out and fades in as the guitar signal amplitude changes.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 06, 2014, 09:35:12 PM
Ok, I fixed J1. It's such a minor revision I didn't bother with a new revision #.

Since I haven't actually built this yet I'm thinking about some other things I could do with the 3 input jacks.

I'll draw some things up and post soon. Stay tuned!  :)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 07, 2014, 06:13:32 AM
Quote from: galaxiex
ExpressSCH came with the switching jacks you see in the schem.

That's actually an unswitched stereo, but no matter.

(http://www.jacksockets.com/images/Phone_jack_symbols.jpg)

A - mono
B - stereo (TRS, Tip-Ring-Sleeve)
C - stereo with two isolated change over contacts (arrows = contacts)
D - stereo with two non-isolated Normally Closed contacts

(http://img.auctiva.com/imgdata/9/8/6/0/1/1/webimg/628003243_o.jpg)

Mono with a non-isolated N.C. contact - what you want.

The term "jack" originates with their use in the telephone system and has been well mangled since, but explicit "jack socket" and "jack plug" helps.  {so you're from "Canadia" - I must humbly apologise for our wandering embarrassment (still, not quite in the class of Pres Shrub who turned up here and gave an arrival speech where he said he was happy to be in "Austria"  ::) ).}


Gain is set by your R4 and R5.  For ratios above 10:1 you can simply approximate the gain as R5/R4, but for lower ratios you have to use the accurate;

Av = (R4+R5)/R4

Av = (100+220)/100 = 3.2

{If it were 10k and 220k then it would be approximately;

220/10 = 22

actually;

(10+220)/10 = 23 }

Some general advice; don't try to do too much with each step, gradualism is good.  Get this going and debugged first, then try the next idea.  If you try to do too much at a step, mods or faultfinding, you can wind up with several things going pear-shaped at once, and faults don't add, they multiply difficulty.  A circuit with two faults is roughly four times harder to fix than the same circuit with only one fault.  This can be a real pain with a new build because it may have several faults, and why we try to tackle problems a stage at a time.  Build, fix, or mod, we always try to cut the problem down to bite size or we just get bamboozled by several faults interacting.

As for the gain overwhelming the trem, really the right place to add gain is after the trem modulator, but I can't see a simple way of doing this (with non-isolated jack contacts) and can only hope that shred and trem are mutually exclusive in use.  We'll see.


{I know that one as "My karma just ran over your dogma"   ;) }
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 07, 2014, 11:03:52 PM
Quote from: galaxiex
ExpressSCH came with the switching jacks you see in the schem.

That's actually an unswitched stereo, but no matter.

Well, all due respect but it does matter. I do like to be accurate in my understanding of this stuff.  :)

I see now... The pointy bit facing the "wrong way" In the ExpressSCH symbol confused me.
I thought that "wrong way" pointy bit was a switch contact. They are close together so that didn't help.
I see now it's a TRS stereo jack.

(http://www.jacksockets.com/images/Phone_jack_symbols.jpg)

A - mono
B - stereo (TRS, Tip-Ring-Sleeve)
C - stereo with two isolated change over contacts (arrows = contacts)
D - stereo with two non-isolated Normally Closed contacts

(http://img.auctiva.com/imgdata/9/8/6/0/1/1/webimg/628003243_o.jpg)

Mono with a non-isolated N.C. contact - what you want.

Ahhh, ok... but isn't that an isolated N.C. contact?
I mean, the contact goes to a solder lug so it doesn't go anywhere unless someone attaches a wire to the lug.

(Just a FYI, I have a drawer full of those.
Stocked up when I had plans to build a tube amp, that may still happen... someday....)

Wouldn't a non-isolated contact mean it is already attached somewhere? Such as to the sleeve? Then it's a "grounding" contact?

Edit; Oh wait... I see now... Isolated and Non-isolated, Got it. DUH!
Got nuthin to do with where it goes. Has to do with how it's isolated from the main contacts. Or not.

The term "jack" originates with their use in the telephone system and has been well mangled since, but explicit "jack socket" and "jack plug" helps.  {so you're from "Canadia" - I must humbly apologise for our wandering embarrassment (still, not quite in the class of Pres Shrub who turned up here and gave an arrival speech where he said he was happy to be in "Austria"  ::) ).}

Hmmm, "jack socket" and "jack plug" is more explicit.
No apologies needed, I'm sure we all have our share of wandering embarrassments.
Maybe some of ours have not made it out your way yet...
Ya, the Shrub made some whoppers but that one has to be one of the most memorable.
We even heard about it here is Canada.. Eh?  ;)  :)

Gain is set by your R4 and R5.  For ratios above 10:1 you can simply approximate the gain as R5/R4, but for lower ratios you have to use the accurate;

Av = (R4+R5)/R4

Av = (100+220)/100 = 3.2

{If it were 10k and 220k then it would be approximately;

220/10 = 22

actually;

(10+220)/10 = 23 }

Some general advice; don't try to do too much with each step, gradualism is good.  Get this going and debugged first, then try the next idea.  If you try to do too much at a step, mods or faultfinding, you can wind up with several things going pear-shaped at once, and faults don't add, they multiply difficulty.  A circuit with two faults is roughly four times harder to fix than the same circuit with only one fault.  This can be a real pain with a new build because it may have several faults, and why we try to tackle problems a stage at a time.  Build, fix, or mod, we always try to cut the problem down to bite size or we just get bamboozled by several faults interacting.

As for the gain overwhelming the trem, really the right place to add gain is after the trem modulator, but I can't see a simple way of doing this (with non-isolated jack contacts) and can only hope that shred and trem are mutually exclusive in use.  We'll see.


{I know that one as "My karma just ran over your dogma"   ;) }

Thanks for the calc's. I don't have the formula's (formuli?) committed to memory but they are easy to look up.
Actually, they are easy to memorize. Add, then divide. I'm just lazy so I look stuff up. When I do it enough times and it gets familiar, then it becomes easier to "just remember" instead of looking it up.  :cheesy:

Good advice to not do too much at once. I do tend to run off and get ahead of myself with new ideas. (not so with my job, see below)
I don't even have the gain board built yet. I'll do that first and see how it works.

Speaking of faults... you might imagine the transmission business can have, shall we say, Problems.
A methodical approach to diagnosing a problem is (in my opinion) essential.
That way, when you fix it, you know the cause and hopefully have a better understanding of the system as a whole.
(guess I'd better apply this to my electronics work, Eh?)  :)

Take my Boss, please.  ;) When faced with a problem transmission he takes the shotgun approach and throws parts at it until it works.
Sometimes he gets lucky and sometimes not. When not... he then dumps it in an employee's lap and says "fix it".
Meanwhile hovering over the poor employee's shoulder every 5 minutes and saying "Well, what did you find?" (no exaggeration, he really does this)
Can you spell f-r-u-s-t-r-a-t-i-n-g?

He doesn't do that with me anymore.
He may be the boss but I let him know that if he wants it fixed fast, he'd better leave me alone.

My Karma ran over My Dogma
Is the way I first heard it. Since then I've seen it that way too.

There's books and bumper stickers and licence plate frames, Oh My!....  :lmao:
http://www.amazon.ca/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=My%20Karma%20ran%20over%20My%20Dogma (http://www.amazon.ca/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=My%20Karma%20ran%20over%20My%20Dogma)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 07, 2014, 11:44:07 PM
3 Wire Safety P*rn.  :lmao:

I added the fuse holder in the original line cord hole. This amp didn't have a fuse!?!?!? Anywhere!?!?!?

The transformer was in the way to put the fuse holder between the original line cord and the speaker jack.... socket.  ;D

Insulated as much as I could, (for now) the exposed line connection points.
Black is Hot, White Neutral.

Not sure if that "Zip Tie" "Cable Tie" is up to code for a strain relief, but it'll do for now.

You can't see it, but there is a star toothed lock washer under the nut for the ground lug.
Ground lug is crimped and soldered.

The writing on the transformer is mine.

In case you forgot,  ;) the last pic is how it looked before.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 08, 2014, 06:35:54 PM
If you compare the feedback network around an op-amp with a simple voltage divider you will notice that they are actually the same thing, the only difference is which voltage is defined and which is to be found.

In a divider a known voltage is applied across both resistors and you find the voltage at the junction.

Vout = Vin * R1/(R1+R2)

When working out the gain of an op-amp you know the voltage at the junction (op-amp inverting "-" input) because its the same as the input on the non-inverting "+" input, and what you want to know is how much voltage is coming out of the op-amp output (or working that backwards to find the required resistor ratio for a desired voltage). 

Av = (R1+R2)/R1

Same as above but upside down.


Here we do not approve of the "scattergun" approach because it's wasteful of time and parts, muddies the waters, can introduce new faults (and also suggests that you don't really know what you're doing).  Diagnose first, replace the faulty part second (and hopefully last).

Hover over my shoulder and you are likely to get splashed with hot solder.  :trouble   I have a rule (which I often break) not to start work on anybodies gear until they have left...  "For God sake STOP HELPING!"

A zip tie isn't a final answer, something like a P-hoop or other clamp to stop the cable twisting inside is the right thing, but the tie will do for the moment.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 09, 2014, 03:41:33 PM
Thanks again for all your help Roly.  :)

I've been mucking with the gain stage and not much luck.
It over-drives the amp too much, even if I lower the gain.
The amp cuts out, farts and squeals.

No matter, I just wanted to see if a bit more volume could be had. For now... no.
I may come back to this later.

Meanwhile... the reverb module came in so working on that.

I'm also working on a schem revision so this might be awhile....

Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 10, 2014, 03:04:23 PM
New schematic.  :)

This is how the amp is right now.

I am trying to puzzle out the reverb section to use the new Belton Reverb Module.

BTDR-1 DIGI-LOG™ REVERB MODULE

The page won't let me link directly, but it's easy to find on the site under the "products" tab.

http://www.accutronicsreverb.com/ (http://www.accutronicsreverb.com/)

I need to reduce the gain of Q2.

The module wants 1.5V peak signal input. The output at Q2 feeding the reverb has about 2V peak if I strum hard
(+ - 2V above and below the "0" center horizontal line). Maybe slightly more.

I have an O-scope and I'll get some pics up later.
---------------------
Here's some pics of the 'scope connected to the output of Q2.

No reverb tank hooked up.

It's a little awkward trying to strum hard and get a steady shot with the camera.  ;)

1V per division on the 'scope.

Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 10, 2014, 11:37:53 PM
Drat! I can't get the reverb module to work.  :grr

I got the output of Q2 lower by replacing R15 10K with a 4.7K.
On the 'scope it shows an average of just over 1.2V peaks with the initial hard strum going slightly over 1.5V

The schematic shows how it is hooked up, but turning up the reverb control just makes 'orrible noises.

This module wants to see +5V and ground.
I can get the 5V using the Zener, and for power purposes, pin 5 has to go to the negative side of the supply.
The signal ground pin 3 and power ground pin 5 are connected internally.
So how do I get a signal ground?
I can't hook pin 3 or 5 to ground cuz then sparks will fly.  :o

I did try a DC blocking cap of 10uF between pin 2 and the wiper of the reverb control.
Should not be needed cuz the data sheet says it has internal caps, and that external caps are not needed.

What am I doing wrong?
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: phatt on August 11, 2014, 05:27:16 AM
hi galaxiex,
Check the voltage on power pin 7 of belton brick,, is it Positive?  ???
Phil.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 11, 2014, 08:00:50 AM
Quote from: galaxiex
The signal ground pin 3 and power ground pin 5 are connected internally.
So how do I get a signal ground?

Re-read;

http://www.ssguitar.com/index.php?topic=3535.msg26608#msg26608
 (http://www.ssguitar.com/index.php?topic=3535.msg26608#msg26608)

Your supply rail is -ve and your ground is +ve, so the module "ground" will be your -ve supply rail and its supply will be via a voltage limiter to the +ve rail, amp ground.

Now we have a couple of interesting minor problems.

R42 = 22k
Module requires 60-100mA
Supply = 22V
Voltage across R42 = 22-5 = 17V
Current through R42 = E/R = 17/22 = 0.77mA

Well that ain't gonna fly.

I'd suggest that the best way to get this would be to use a 3-pin regulator (which may need a bit of heatsinking at this current and supply voltage).  Using a 7805 regulator the centre "ground" pin needs to go to the -ve supply rail, and the left-hand input to the amp ground (+ve), the right-hand 5V output pin to the reverb unit +ve.

P = E*I
17 * 0.1 = 1.7W so it's going to get hot.  You can stick a resistor in series with its input leg to drop most of the supply so the resistor gets hot instead.  It needs at least 3V of headroom so the minimum input voltage at maximum current should be 5+3 = 8V, let's say 10V, leaving 7V to drop at 100mA;

R = E/I = 7/0.1 = 70, 68 ohms.
P = E*I = 7*0.1 = 0.7 watt, so a 1 watt should do but I'd use a 5W wirewound ceramic.

N.B. the mounting tab is connected to the middle leg which in this case is the -ve supply rail.

{I hope the supply has enough in reserve to run this module}

The second minor problem is that the module input impedance is only 10k so it's going to rather seriously load the output of the reverb driver, however you want to lose a bit of signal level so this should work out with the original 10k load and the emitter bypass adjustment.

The best way to reduce the gain of the reverb driver without altering its DC conditions is to tap its emitter bypass cap down the emitter resistor (say using a trim pot).

Erratum: D2 is in the wrong place.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 11, 2014, 10:04:35 PM
Re-read;

http://www.ssguitar.com/index.php?topic=3535.msg26608#msg26608
 (http://www.ssguitar.com/index.php?topic=3535.msg26608#msg26608)

Yes, Thank you.  :) This keeps tripping me up...
I don't know why I have such a hard time wrapping my head around it....  :duh
If I keep working on this amp I'll "get it" ....eventually...

The zener output measured about .6V when connected to the module... so ya, no good.
Thanks for the math.
I gotta start using/working with these equations more often so I get familiar with them.

3 Pin regulators of the LM78XX variety I got lots of.

So as a quick and dirty test I rigged a LM7812 feeding a LM7805,
clipped that and the module into the amp and no go.

The module drags the supply down to 10V or so.
Unplug module... voltage comes back up to 20V.

The other changes (put back the 10K R15 and the trimmer on R16 / C11 I can easily do.
But no point yet until I get a transformer with a higher VA rating.
(I assume that's what it needs)
I need to make a parts order at DigiKey anyways...

They really did design this thing down to the last cent.
Bare minimum ratings for everything I'll bet.

I have an ammeter and considering putting that in series on the DC supply side to see what the amp is pulling for current.

"Erratum: D2 is in the wrong place."
Soooo easy to miss stuff, even when you've checked it all several times and think you caught all the mistakes.
Nice to have another set of eyes look at it.  :)

Thanks for the changes on the schematic,  8|  I'll get that fixed up too.
I think it's getting easier to read with every revision.

OT stuff...
Surprised no one mentioned the S-51-A Telequipment Serviscope I have.  :D
It's a bit flakey at times, the Y axis drifts around some.
I have a service manual for it I found on-line, but not got around to looking into that yet.
Vacuum tubes and high voltage!!! inside!!! I WILL be careful!!!
Mostly to make sure it's unplugged and caps discharged before working on it.
And yes, I know the CRT acts as a capacitor and can store a very big charge.
I did "upgrade" the burnt out pilot light to an L.E.D back when I first got it.
It was a free give-away from a Tech that bought a new Digital 'scope.

Enough blather... back to work...

Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 11, 2014, 10:59:29 PM
Update;
Amplifier current draw and voltage.

No reverb module
Idle                      24.3mA   19V
Strumming hard      62mA     19V and down to as low as 15V on peaks

With reverb module
Idle                       191.5mA   10V
Strumming hard       200mA     10V not much change, might vary a few mV, distorted sound. (sounds kinda neat actually, like an old fuzz pedal)

Measurements taken at main filter cap.

So a .5A or better transformer and maybe a 1A or more diode as the existing one's rating is unknown.

Perhaps this one...

http://www.digikey.ca/product-detail/en/241-5-16/595-1046-ND/952916 (http://www.digikey.ca/product-detail/en/241-5-16/595-1046-ND/952916)

Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 12, 2014, 09:12:26 AM
hi galaxiex,
Check the voltage on power pin 7 of belton brick,, is it Positive?  ???
Phil.

Hi Phil sorry I missed your post earlier.
Thanks, yes +V on the module. As you can see it's getting sorted out.  :)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 12, 2014, 10:14:02 AM
Quote from: galaxiex
The module drags the supply down to 10V or so.
Unplug module... voltage comes back up to 20V.

You will note that I came directly off the main filter cap, not after the 1k decoupling cap for the preamp, but this is not entirely unexpected.

The only way around this I can see is to add more supply, say a 9V or 12V DC plug-pack rated at 100mA or more + 7805, i.e. build it in where space permits.  This is certainly something you could just lash up to confirm that the signal arrangement works as intended.

Or...
Quote from: galaxiex
But no point yet until I get a transformer with a higher VA rating.

I'd also consider changing the rectifier to a bridge arrangement, half wave is a bit ...erm... "basic".

I have to observe that this module seems to be a bit of a current hog compared to the way most stuff is going these days.

"Every non-trival programme has bugs"
Every non-trivial circuit has errors.

In general you should never check your own work - if you overlooked it the first time you are likely to go on overlooking it.

Quote from: galaxiex
Surprised no one mentioned the S-51-A Telequipment Serviscope I have.

Oh I noticed all right  ;) , nice score, I'm a CRO collector and buff and if you want to start a specific thread on fixing it up a bit later I'm available to assist.  Some background here;

http://www.ozvalveamps.org/testgear.htm#cros (http://www.ozvalveamps.org/testgear.htm#cros)

With the exception of the sweep generator CRO's of this vintage are pretty similar to a stereo valve guitar amp, and the kind of faults that turn up are also pretty similar to what turns up with guitar amps, high resistors leaky caps and duff valves, but dirty switch contacts and pots in particular - they ain't as exotic as they look at first glance.

Quote from: galaxiex
I have a service manual for it
Which I would love to have a copy of if you could (my e-mail is in my profile).

Presuming you have measured the AC voltage out of the current tranny, that looks like it would do, but with the increased current and a half-wave rectifier I'd also consider bumping up the value of the main filter cap, say 2200uF.

With these inexpensive amps the only way to go is up, and the more they were trimmed down to the last cent the more altitude is available for improvement.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 12, 2014, 08:42:26 PM
Yep I was taking power right off the main filter cap for the v-reg and module hack test.

I've ordered an X-former but for a test I'll rig up a wall-wart and the 5V reg and see what happens.
I'm sure I've got a 12V 500mA wall-wart around here someplace.

Ya I didn't care for the half wave supply either.
I've got some bridge rectifiers and loose diodes so could do either old school 4 diodes on a terminal strip or go "modern" with a bridge chip. I also have some large value caps that need a home.

I emailed you about the 'scope manual but you're probably sleeping right now.

I haven't looked at that link yet but much thanks  :) for the offer of assistance later in a new thread on the 'scope.
I think I did spray the pots and switches (proper contact cleaner) some time ago, and it helped, but it still needs some attention.

For now gonna focus on getting this amp the way I want it.
Also got 2 more old SS amps in the line up that need attention/mods...


Warning
Random thoughts, background, and other off-topic blather....

Not sure if any other folks are following this thread....

I know I'm polishing a turd here.
Doesn't matter, I want to do it.
Had this amp as a kid bla bla etc...

I got into messing with electronics a long time ago but no formal education in it.
Experimented with circuits I found in books, built all kinds of little battery powered gadgets.

One of note was a laser "bug".
Bounce a laser beam off a window and capture the reflected beam with a rifle scope focused on a receiver with a photo diode and small amp to headphones.
I actually got this to work... sort of... picked up a lot of building noises and the occasional garbled conversation.
Was easy to do when I lived in an apartment building with other apartments directly across from my 3rd floor apartment. setup laser and Rx on tripod etc...
Now live in a house... no line of sight windows around... just as well...  :loco

Built test equipment, a Dual + - variable power supply for powering Op-amp circuits . Capable of + - 30V at 1.5A
And a single variable supply 30V @ 3A.
Phase locked Freq generator. 1, 10, 100, 1000 Hz 5V peak square wave.
It phase locks to an FM audio signal.
Built it from plans in Radio Electronics or some such magazine.
I used to subscribe to...
Radio Electronics
Modern Electronics
Popular Electronics and a couple others I don't remember.
Saved all the old issues until a few years ago... long gone now.
Back issues on-line tho... not the same as holding one in your hands.

Went on to fixing friends and others car stereos, car amps, home stereos,and what-not.
Was not afraid to take anything electronic apart, esp if it had a problem.
Diagnosed/troubleshoot by "feel, guess and by gosh", and sticking voltmeter probes everywhere, got lucky most of the time... sometimes not. Smart enough to know where to be cautious about sticking the probes...

"Just enough Knowledge to be Dangerous"

One memorable one was a friends motorbike electronic ignition module. He was a student so no money.
Dealer wanted $350.00 for a new module that had about $5.00 worth of parts in it.
It was also potted and sealed. I cracked it open, (what do we have to lose?) and found a broken trace on the board right at the connector. Poor vibration mount. REAL important on a motorcycle.
Fixed it with some wire and solder. He thought I was a genius. Saved him bucks and got his ride back so he could go to school.

Rarely applied ohm's law and other formula. Copied stuff out of books.

Left electronics for a long time.... 5-6 years or more.
I had/have a whole spare bedroom/hobby room with all this electronics stuff in it collecting dust.
Forgot most of what I had learned.

Then got into radio controlled airplanes. Flew FPV right from the start around 2007.

FPV = First Person View.
Mount tiny security camera and vid Tx in model airplane and have ground station with vid Rx.
Feed vid to VR goggles and bam! you are "in" the plane flying around.
If you care to do a search FPV has really come a long way for the hobbyist.
Early FPV days you had to make stuff work that wasn't intended to work with other stuff.
Now you can buy turn-key systems off the shelf and go fly.
On Screen Displays, Return to home, GPS, Stabilization systems, Head Tracking, etc... it's cool geeky stuff.
Probably you've heard of "Drones" and the "menace" they are reported to be. Blech!
Most are just hobby guys having fun.

Left the airplane hobby and electronics again... still got planes new in boxes stashed away.

It's been the same with playing guitar. Play for awhile... rest... etc...

Right now in a band with a great bunch of guys (and girl singer, man she can belt it out!)
so probably will stick with it for a while.

Then found this amp on eBay. Electronics, Here we go again.

One of my FPV vids....

https://vimeo.com/5486211 (https://vimeo.com/5486211)

Cheers!

Edit; looked at your CRO page, Wow! lots of info, cool stuff. Thanks!  8|
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 13, 2014, 04:39:26 AM
Quote from: galaxiex
you're probably sleeping right now.
These days I seem to spend most of my time sleeping.  As I say to SWMBO, "I'm just off for a nap ... before I have a snooze ... to get ready for a good sleep."   xP

Quote from: galaxiex
I know I'm polishing a turd here.

You want to do that to make money/a living, you're raving mad.

You want to do it for self education, curiosity, or just the hell of it?  Nuthin' wrong with that.  My place is full of well polished turds.

1256 views in 17 days ain't just us chickens.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 13, 2014, 08:30:23 PM
 :lmao: Thanks for the humor guys!  :lmao:

I needed that just now.  ;)

I had hoped to try the wall-wart power supply last night but... best laid plans and all that.... oh well.

Today the transformer came in (DigiKey ships fast) so tonight I'll get to hooking that up with a bridge rectifier and see how it goes.

Cheers!
Dale

Edit;

Roly, SWMBO?

"You want to do it for self education, curiosity, or just the hell of it?"

Yup, all of that.  :)

Nice to know I'm not the only one that polishes turds...  :lmao:
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 13, 2014, 11:32:21 PM
Well I got the schematic done with a few additional minor changes.
Cleaned up the trem circuit a bit and added the bridge and reg's for the reverb.
Found and fixed a mistake that crept in... R38 on the trem pot somehow got changed to 47K, should be 4.7K

Any other mistakes I missed?  :)

Perhaps add a couple of small bypass caps on the reg outputs?

Have not got the actual changes/mods done to the amp.
Got the transformer mounted and now puzzling out where to put everything else.

Circuit/component changes/repairs are relatively easy compared to (some) hardware changes.
It's a challenge figuring out where/how to mount all this stuff... and have it look neat.
Not much room in this chassis....

I'll post pics when I get it all installed.  :)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 14, 2014, 05:08:14 AM
SWMBO - "She Who Must Be Obeyed"

It derives from "Rumpole of the Bailey" by the British writer and barrister John Mortimer, and starring the late Leo McKern in the TV series.

Rumpole's wife Hilda, the daughter of a judge, was a dragon who was permanently disappointed that Rumpole was content to be a rather shabby barrister in criminal practice with no ambition to "take silk" and become a QC, and thence be elevated to the bench.  Despite his "common" tastes in food and more than a little wine, Rumpole was a man of letters given to literary allusions and quoting the classics, and his tacit references to Hilda as "She Who Must Be Obeyed" is a reference to the fearsome queen in the adventure novel She by H. Rider Haggard.

{My step-father similarly would refer to my mother, an avid gardener, as "The Grounds Committee" because we were often roped in for the heavy lifting on her projects.}


Quote from: galaxiex
Perhaps add a couple of small bypass caps on the reg outputs?

Yes.  I habitually put a small (0.01-0.1uF) cap on the input and output to ground right at the regulator ever since I had one take off at 50-odd MHz and cause no end of hair tearing in a logic system build.  (both regs in your case)


2v2 erratum:  module pin 5 "ground" should go to the "ground" connection on the 5V regulator, i.e. -ve supply, not amplifier ground.  {I'll be glad when you finish this project and I can stop standing on my head to look at the circuit.  ::) }
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 14, 2014, 08:58:26 PM
Ahhh, SWMBO...  :)

I found some clips from the show on YouTube, not watched enough to form an opinion, but it looks like something I would like.  :)


{I'll be glad when you finish this project and I can stop standing on my head to look at the circuit.  ::) }

 :lmao: :lmao: :lmao: :lmao: :lmao:

I've not laughed so hard in a long time.

THAT was FUNNY!!!  :lmao: :lmao: :lmao: :lmao: :lmao:

It'll be done soon... I hope... or I could take a break from this and get to building the speaker cab.  :)

I fixed the schematic above.

Ground on the reverb module
Added caps to the reg's
Changed the V+ and V- pins on U1 input buffer. Good catch from J M Fahey. Thanks!  :)

Edit;
The original transformer output measured 16.5 VAC with no load, nothing connected to it.

The new transformer output is rated as 16 VAC at full load, (800mA).
With no load connected it measures 20VAC.
This will certainly give me some PS headroom, but I'm wondering if it might not be too much?
Once I get the bridge rectifier and filter cap hooked up I'll check the DC output with no load.
I know the unloaded DC output will be more, and I'm sure there is a formula...  ;)

Forgot to mention, the original PS diode had markings on it indicating a 1A rating.
Still gonna use the bridge instead.
Also will look at all the cap voltage ratings in case the new PS goes over any of them.

I can, of course, always obtain yet another transformer with a lower voltage secondary.

Edit 2;
The new supply has 26.5V DC unloaded.
With only the reverb module (and the 2 regulators) plugged in it drops to 22.6V DC
so I think we are good to go!  :)

Next; plug in the amp board and see if we let the smoke out of anything.  ;)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 14, 2014, 11:58:29 PM
Success! ... sort of...

Reverb and amp all hooked up. Idle 22V
Hard strumming at full volume and it never drops below 21V.
The amp is still "not loud" at full volume, but it's again much better than before.
The increased PS stability seems to help.
With some decent efficient speakers it should be very good.

The reverb "sorta" works...
It hums very loudly and cannot turn it up too much. The hum gets very loud past 3.
There is a reverb effect in behind the hum.
It's more of a distinct "echo" or like a double note.
Almost like a digital delay with a medium/long single slap-back echo.
But the echo is at least the same volume if not louder than the first picked note.
Not pleasant at all...

I'm not sure if the problem is on the drive side, recovery side, or both.
Or maybe I damaged the module with the first test when the voltage dropped?
I didn't get the trimmer installed on R16 yet. Not much room on the board there.
It will take some fiddling to get that done. I'll try that next.

BTW, the heat sinks on the regulators for the reverb get pretty hot.
Cannot hold your finger on them for long, couple of seconds and it's very uncomfortable.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 15, 2014, 09:31:48 AM
(http://www.anorak.co.uk/wp-content/uploads/2012/08/australia.jpg)


Excessive hum?  Hummmm.  I go back to my earlier suggestion of a DC plugpack or similar (module ground to amp ground).
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 15, 2014, 12:18:17 PM
Dear J M, this is the current schematic and how everything is hooked up.

The new transformer has a center tap so, yes, that's a great idea to use that for a low Voltage supply.  :)

Roly, I didn't post this last night... it was late and I was tired,
but I tried a large value resistor is series between pin 1 of the reverb tank and the reverb pot.

The reverb and hum both got better so I kept increasing the R value until I got up to a 5.1M resistor. Yes 5.1M.
Hum was almost gone and the reverb sounded "more ok". No more double note and more echo-y like a reverb should.
I have higher value R's I think... (at work right now) but I stopped there as I said, it was late and me tired...  ;)

... but another issue came up.
It was sounding good so I kept playing... and after 5-10 minutes the voltage dropped and the amp sound cut out completely.

I think the regulators overheated. I quickly switched off, waited and switched back on. worked for 20 sec and cut out again.
That's when I called it a night.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 15, 2014, 10:44:32 PM
Thanks J M,  :)

I made those cap changes and some other slight re-draw of the schematic.

Of note, I added +Ve symbols to help keep in mind the "positive ground chassis".

I will not re-draw the reverb PS, until I have a working setup on the bench. (polish, polish, polish....)  ;)

I just happen to have a small, 300mA 12V transformer in my stock of parts.

I'm thinking to put back the original transformer to power only the amp board (with bridge rectifier and 3300uF cap) and adding the 12V transformer, bridge, 5V regulator, and filter cap for just the reverb module.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 16, 2014, 06:56:15 AM
Some mods work out, others don't.  When things start getting complicated it's time to back off and try a different tack.

Attached is a sketch of what I think will work.

The reverb module supply is independent of the main amp supply, only sharing the amp ground.

I've added an emitter follower to provide a lower impedance drive to the 10k module input impedance, and a cap on the output (coz I'm a little dubious about the module internal caps)  A resistor to ground might be required at the module input and output, say 47k each.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 16, 2014, 07:59:44 AM
Roly,
Thanks very much for that, and I certainly will try that. But..... new problem...

I think there is a basic problem with the amp itself.

I decided to try powering the amp only (no reverb module) from the new supply.
Monitored voltage right at the supply connection to the amp board. 25.XX volts powering just the amp.
All good so-far.
(I found the data sheets for the 2SB175's and the 2SB324 output transistors.
They are in Japanese but fortunately the numbers are not.  ;) )
2SB175 max -Vcbo 30V
2SB324 max -Vcbo 32V

A bit close to the 25V of the supply but within the rating? I think?

So, amp plugged in playing guitar, sounds good,
Louder that ever, slight pleasant distortion, voltage at PS output 24-25V ok.
30 seconds in the voltage drops to close to 0 and the amp (of course) goes quiet.
No nasty noises, it just fades to nothing.

Please correct me if I'm wrong, but I think one (or more) of the transistors is breaking down and "shorting".
I "think" this amp should be able to handle the 25V supply.
IF that is so, I need to find the fault causing it to cut out.
(a chance to practice my diagnostic skills)  :)

Or...

Do you think I could possibly replace the transistors with silicon? Possibly 2N3906's?
Or would we have to extensively re-bias everything?
At this point I don't care about the work involved.
I've spent so much time on it already I may as well go whole hog.
Why not  :)

Your thoughts please.  :)

Edit;
I'm gonna go put the ammeter in series with the supply (and monitor voltage)
and see what the current is doing at fade out.
I'm gonna guess current goes up.... lots.... and maybe I'll let the smoke out of something....

Will report back...
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 16, 2014, 08:24:32 AM
Yep, as suspected current gradually goes up after 20 seconds of playing and then spikes to O/L on the meter.

As it does this there is a quiet hum that starts and builds but does not get very loud at all.
At that point I'm quickly switching the amp off.

Now to try and pinpoint the cause....

BTW the 2SB175 and 2SB324 transistors are available online but may be of questionable quality...
I may be able to sub 2N404 for the 2SB175?
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 16, 2014, 10:15:54 AM
Yes I think you are correct.  :)

I just went in and replaced ALL the 16V rated electrolytic caps for 25V or better rated caps.
The exceptions were the three .47uF caps that have 25V rating so I left those.

The amp is easily twice as loud as before,
I actually had to turn down the volume control and at "3" it's still a decent bedroom volume.

Still fades out after 20-30 seconds of playing.

A "real" amp inside the cabinet is still on the table as an option....
but I'd want it to have reverb and tremolo working too.

Got any schematics or donor amp candidates in mind?  :)

Or... maybe I can find some substitute output transistors...?  Re-bias likely needed.
There's gotta be some higher power rated PNP germs out there? Probably expensive... ::)
Or silicon that would work?

I can see the next limitation being the phase transformer....  :blank:
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 16, 2014, 11:34:48 AM
HAH!
I found a pair of 2N2148 PNP Germanium T03 package in my junk. Way overkill I'm sure....  ;)

Quick and dirty wired them in with alligator leads (removed original 2SB324's of course)...
and it works!

Sound is a bit distorted and need the tone control at "0" else it squeals.
Maybe because of the long leads to the transistors?
Or biasing issue. Or both.

No heat sinks on the 2N2148's, they got barely warm after 5 minutes of playing and the amp did not fade out!
Yay!

Voltage stayed up around 24-25V. Didn't check the current.

I think I got some T03 sockets around here someplace....  :)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 16, 2014, 08:56:40 PM
Alright, I got the new transistors mounted. :)

The amp is sounding better than ever.
It's got some volume, tho not earth shaking.
Bass response has improved (which was another thing I hadn't mentioned yet, and wanted to fix).

The tremolo now has an interesting "pulse" or "throb" in behind the note that sounds kinda cool.  8)
I like it!

The tone circuit does need some attention because at 10 the sound has a harsh ice-pick distortion.
Tone at 4-5 and it sounds great!

Check out the pics and let me know what you think.

Now to get back to working on the reverb...
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 16, 2014, 11:37:28 PM
Roly, in your circuit above did you mean to draw the transistors Q2 and the added one as PNP type?

I have some 2N3906.  Suitable?
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 17, 2014, 06:01:14 AM
Doh!   :duh

(http://1.bp.blogspot.com/-R53dFKJEL8U/TZPawv0s-1I/AAAAAAAABC0/cTBHbtKAUDM/s1600/internet_-_it_doesnt_make_you_stupid_it_just_makes_your_stupidity_more_accessible_to_others.jpg)

1) for letting the blood rush to my head.  Sorry, just think, "add an emitter-follower".

2) getting the wrong datasheet and thinking "silicon".

That "heatsink" is a joke.

Grab a fan-blown CPU cooler and thermally couple it to that.

You could try increasing R25 which feeds the bias chain, say try 2k2 and see if that cools it down a bit, may also reduce output power a bit.

Try to avoid running it into thermal runaway - it isn't healthy.

The driver Q4 might need some thermal attention too.

Get some heatsinking in there!  As a germanium amp these really don't like heat.

{sorry again  :-[ } 
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 17, 2014, 07:32:36 AM
Doh!   :duh

1) for letting the blood rush to my head.  Sorry, just think, "add an emitter-follower".

Ummm ok, no apology needed. I can figure out an emitter follower.

2) getting the wrong datasheet and thinking "silicon".

Again, ummm,
in reference to what? The emitter follower?

That "heatsink" is a joke.

The stock original heatsink?... or the brackets I made for the 2N2148's ?
Because the 2N2148's run quite cool and don't even need heat sinking.
The brackets merely hold them.

Grab a fan-blown CPU cooler and thermally couple it to that.

You could try increasing R25 which feeds the bias chain, say try 2k2 and see if that cools it down a bit, may also reduce output power a bit.

Try to avoid running it into thermal runaway - it isn't healthy.

The driver Q4 might need some thermal attention too.

Get some heatsinking in there!  As a germanium amp these really don't like heat.

{sorry again  :-[ }

Again, no apology needed but I am confused.... ???
Are you suggesting I put the original 2SB324's back in with proper heatsinking?

For R25, I don't really want to do anything to reduce the output...
...unless you think it's really needed with the 2N2148's.

Thanks for the data sheet, that's the one I found too.  :)

Are you ok Roly?
The above was not your usual clear concise post.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: J M Fahey on August 17, 2014, 08:59:35 AM
Maybe he already got sick of this endless thread.
Sorry.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 17, 2014, 09:07:56 AM
Maybe he already got sick of this endless thread.
Sorry.

I would not be surprised...

Am I annoying everyone with this?
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 17, 2014, 11:16:24 AM
Not at all, I'm finding it "interesting" to try and go back lebenty-leben years when I was wrassling this sort of gear on the bench, where the red wire was actually -22V; and this "asian" PNP format is still really confusing to somebody brought up in the British school of circuit drafting, voltage rails stacked by polarity/potential and the stages strung in between.  {Worked on Decatron pill counters and such that had several supply and bias rails stacked up from most negative on the bottom.}

The previous was intended to only be diagrammatic with that in mind, you need to be mindful of the details (and well-intended bum advice).  So my excuse is that the drive amp representation is "conceptual" - okay?   ;)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 17, 2014, 12:59:37 PM
Okay.  :)

With that cleared up...

I've been playing this amp for awhile now with the 2N2148's and it seems to be good.
With no effects in use the amp stays clean to max volume as long as the tone control is not above 6-7.
I have some ideas for that...

I've cobbled up a separate 5V supply for the reverb with the ground of that going to ground (+Ve) on the amp.
No more hum, but I did not yet put in an emitter follower.
I have C11 dialed completely out on Q2 and it's playable at low reverb settings.
Much past 4 and reverb gets over the top and all goes to mush.
At 10 its on the edge of oscillation/feedback and does oscillate if tone gets turned up.

All this stuff is interacting somewhat of course.
I expected that.

So 2 things... need to tame the tone control and get the reverb levels sorted.

I'll do the emitter follower first and see what happens,
but for now gonna take a break from wrassling with this thing.

I AM gonna wrassle this thing to the ground and make it beg for mercy. :)

Some might call it stubborn...

I call it dogged determination.  :duh  :)

BTW just a point of interest...
The reverb module specs say 100mA... but actual testing show it drawing @ 167mA.
With that in mind and to have something to compare, I have ordered the "newer" small reverb brick BTDR-2H labeled Accutronics rather than Belton.
Probably both made in the same factory somewhere in Asia anyway....
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 18, 2014, 09:47:26 AM
Got get'um Tiger!   :dbtu:

Quote from: galaxiex
actual testing show it drawing @ 167mA

Woah,  :o  that is seriously unhelpful; that's a almost three times "typical", and 50% over "max".

{I hate that, when the datasheet lies.  :trouble }
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 18, 2014, 12:06:07 PM
{I hate that, when the datasheet lies.  :trouble }

Ya, not sure if the data sheet is lying, or something is wrong with the one I got.  ::)

That's why I ordered another one.  :)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 19, 2014, 04:51:26 AM
hmmmm  ???

These digital sorts of things tend to work or not, no half measures, (however ...)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 28, 2014, 07:29:56 AM
Ok, Had a nice break... back to it.  :)

And back to basics...

I came across this thing called SWTC, (Stupidly Wonderful Tone Control), and some modified versions of it.
In the schem I have used the SWTC 2.

Here I have stripped down the schem to "back to basics" to get the basic amp sounding good.
I didn't like the tone control and how it caused the amp to sound bad with tone on 10.
Also the volume control was not very "linear" so to that end we use an audio taper pot.  ;)
Besides, the original pots were still a bit scratchy even after using spray lube/cleaner.

I've not yet made these changes to the amp but will do so tonight after work.

After I get the basic amp sounding good, I will add back in the reverb circuitry.

Note that compared to the last previously posted schem, I have eliminated Q2 and its associated parts.
Q2 was the original reverb driver which we don't have to use,
and now have the option of using it for an added gain stage or whatever.
The reverb can also be tapped into the signal chain at whatever point we want, but that's all for later...

I have also been considering trying different (silicon) transistors for Q1-3-4 but again... later...

This is becoming an almost complete re-engineering of a cheap amp that would have been easier to just gut the thing and put a "real" amp in it.

I don't care, I'm having fun and learning lots.  :)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 28, 2014, 08:37:12 AM
 :dbtu:
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 29, 2014, 12:00:00 AM
Thanks for the thumbs up Roly.  :)

So I got home and wired this up just like the schematic shows.

One exception... R7 at the base of Q1 is actually an 18K, not 10K.
Somehow that mistake crept in and I never noticed.
It's always been an 18K all along. (I'll fix the schem later)

Ok, so the amp is very loud and distorted like this. (BTW, the Trem still works  :) )
With Tone and Vol up full it squeals horribly.
Squeal (barely noticeable under the distortion) starts at about 6 on volume and gets worse as Vol increases.

At very low Vol it's "almost" clean. Any tone setting.

Can find a "sweet spot" balancing tone and vol to where it's a nice crunch but kinda muddy, lack of treble.
(But it will sustain for days...  ;)  :lmao: )

As an experiment I disconnected the buffer output after R4 10K, (so no signal on R5 at all) and jumped it to the junction of C7 and R11.

Still quite distorted (any vol except very low) and not a pleasant distortion.

My (random) thoughts/ideas/questions... no particular order... and I'm just guessing...  ::)

1. Leaky germanium transistors can't take the good solid guitar signal from the buffer.
2. Simply too much gain somewhere for what the circuit can handle.
3. The tiny little phase transformer is saturating and not in a good way...
4. Replace all germs with silicon (one at a time and bias them appropriately? ), see what happens...
5. The above may not work because of the phase transformer?
6. Go back to 50K pots as those were probably bleeding off some signal to ground?
7. Figure out a way to eliminate the phase transformer?
8. The "power amp" section just can't handle a decent signal?

I've got small signal JFET's and BJT's and small MOSFET's etc, etc.
Even got some 2N404 germanium transistors.

Lots of questions and possibility's....

Where do I start?
Where would you start?
(besides gutting it and putting a real amp in it, still a possibility...)  ;)

If I gut it, I still want Tremolo and Reverb to work.
I would need a preamp schem I can copy or...
Design my own? That may be over my head right now...

I do have this 60W to 100W compact power amp board kit from here...

http://www.lh-electric.net/projects/pa100ws.html (http://www.lh-electric.net/projects/pa100ws.html)

Thanks for any ideas you can throw my way.
I'm a little lost right now... Not discouraged, just not sure what to try next.

Edit; BTW I did physically remove Q2 and all associated R's and C's from the board.
Just in-case there was some parasitic signal bleed or whatever...
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: phatt on August 29, 2014, 07:23:58 AM

8. The "power amp" section just can't handle a decent signal?

Lots of questions and possibility's....

Where do I start?
Where would you start?
(besides gutting it and putting a real amp in it, still a possibility...)  ;)

Thanks for any ideas you can throw my way.
I'm a little lost right now... Not discouraged, just not sure what to try next.


You start by reading; :-X

How about you go do some reading it will save you from all the frustration. 8)

http://sound.westhost.com/site-map.htm

Under *Articles*
Start at *amplifier basics* and work down, it will help you a lot. 8|

Also look at some of the project pages for ideas.
http://sound.westhost.com/projects-0.htm#pwr

That site is huge and bursting at the seams with well written material for the novice. :dbtu:
Cheers, Phil.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 29, 2014, 09:00:52 AM

You start by reading; :-X

How about you go do some reading it will save you from all the frustration. 8)

Thanks Phil, I will do that.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 29, 2014, 11:08:54 AM
Quote from: galaxiex
With Tone and Vol up full it squeals horribly.

Instability.  Your amp is acting like an oscillator.


The conditions required for oscillation are the opposite of the conditions required for amplifier stability.

For an amplifier to oscillate there must be a feedback loop (albeit unintended) with gain, and a phase shift at the oscillation frequency which brings the feedback in phase with the output - positive feedback.  For oscillation the loop gain (forward gain less unintended feedback loop losses) must be greater than unity.

Finding this loop and killing it is your Target For Tonight (http://en.wikipedia.org/wiki/Target_for_Tonight).


How we prevent stages from oscillating is firstly by supply de-coupling, then spacing and shielding, keeping long runs at low impedance, careful grounding paths, etc.

You have upped the primary filter cap C24, the next important one is C16/220uF after the decoupling resistor R24.  Then there is no more decoupling.  So, add another 1k in series with the supply line to the front end (may have to cut a track; just above "vol" on cct) and add a bypassing cap somewhere close to Q1.


Fit ground shorting input jacks.  No.1 now has a very high input impedance and is wide open.  Just a few pF's of strays and she's coupled.


Quote from: galaxiex
Where do I start?
Where would you start?

"Start"?  START!?!?  :trouble Your circuit is already at rev3.0 and counting!  You're on the third lap already.

Review this thread man, look around you, you are already in it knee-deep!  :duh  {And having a great time it seems to me}   :dbtu:

Now you have a hacking amp with some demonstrated potential (the trem), and a few problems.  Instability, particularly as you are modding a design, can be most interesting and educative, this is the wild unexplored Great Unknown for you to blaze a trail - Technician vs. Universe - who will win and bring order out of chaos?

{when I was doing industrial stuff I carried a lot of tools and equipment, but I also carried a real Magic Wand(TM,C,P)*, and at times I have produced it and done a "nothing up my sleeve" before "pulling a rabbit out of a hat" and starting the (previously) faulty machine.  (overheard: "yeah, he's @#$%in' nuts, but he can nail jelly to a wall"  :lmao: )  *This is also my "calibrated tap" for finding microphonics preamp valves}

We reduce each problem to bite-sized lumps, then break them down into nibbles.

The power supply now seems satisfactory (if not actually magnificent).


You were having thermal runaway (in the output stage?).  After all your supercharging we need to have a look at the output stage, its biasing, its thermal compensation (lack of), and its dissipation/heatsinking; its DC and thermal conditions.  I'm pretty sure that the bias tree R25/6/7/8 requires trimming, AND it has no thermal comp (so no wonder you are getting thermal runaway) so that also needs a mod.

Then we need to look at the AC conditions, is the driver doing the required job?

Then back another stage; stable?  Sufficient?

Finally the inputs, and a fully functional amp.

And from that stable foundation you can then tinker and mod with confidence.

HTH


{Ref: cct rev3.0;
http://www.ssguitar.com/index.php?action=dlattach;topic=3535.0;attach=4841 (http://www.ssguitar.com/index.php?action=dlattach;topic=3535.0;attach=4841)}


PS
Quote from: galaxiex
By the way after that last post I went back and scoped the amp and the signal after the phase transformer is def clipping.
Far too much gain and hitting the rails.

Steady champ, remember this is power (E&I) drive you are looking at, and the transistor bases look a bit like a clipper to the driver, could be normal.  First the DC conditions for the new supply.


edit to add...

Before 100W-RE.gif, first I think maybe;
http://sound.westhost.com/project03.htm (http://sound.westhost.com/project03.htm)

or

(http://i1341.photobucket.com/albums/o743/Roly49/Twin-50/Twin-50-120321_zpsfe584a1e.gif) (http://s1341.photobucket.com/user/Roly49/media/Twin-50/Twin-50-120321_zpsfe584a1e.gif.html)

then;

http://sound.westhost.com/project27.htm (http://sound.westhost.com/project27.htm)



Grouch: lookit this in isolation;

(http://www.lh-electric.net/img/100W-RE.gif)

What does it tell you without the component values?

Compared with;

(http://sound.westhost.com/p03_fig1.gif)

{"you never find just one roach in a kitchen"}

Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 29, 2014, 09:04:25 PM

Instability.  Your amp is acting like an oscillator.

Thanks for your explanation of this.  :)

Target For Tonight.... I will...

1. fit a shorting jack
2. increase? C16 to 1000uF or whatever I can fit there.
Is there any benefit to adding a small 0.1uF in parallel with C16?
3. add a 1K in the supply line to Q1 and decoupling cap nearby. Value? Large? Small? Both? I'll experiment...
4. ... and other things as I think of them... but one at a time! so as not to lose the rabbit.

"Start"?  START!?!?  :trouble Your circuit is already at rev3.0 and counting!  You're on the third lap already.

Review this thread man, look around you, you are already in it knee-deep!  :duh  {And having a great time it seems to me}   :dbtu:

Ha Ha!  :lmao: Yeah, I should have said "where do I start from here"

Neck deep more like it...

Yes, having a great time!  :) Learning is FUN!  :) Esp. with such wonderful help here!  8)
Someday I hope to be able to nail jelly to a wall...  :lmao:

Magic Wand? Magic Wand?!!! In my trade (transmissions) I have a Magic Wrench,
I'm the guy they all bring the "tough" problems to...
I pretend to have a secret that keeps the others all in mystery and wondering "how did he fix that?"... (snicker)
If only they knew....
I'm just a little dense when it comes to this amp stuff...  ;)

Ahhh yessss, bite sized...

The power supply now seems satisfactory (if not actually magnificent).

Magnificent! Holy carp! High praise indeed. Thank you!  :)

You were having thermal runaway (in the output stage?).  After all your supercharging we need to have a look at the output stage, its biasing, its thermal compensation (lack of), and its dissipation/heatsinking; its DC and thermal conditions.  I'm pretty sure that the bias tree R25/6/7/8 requires trimming, AND it has no thermal comp (so no wonder you are getting thermal runaway) so that also needs a mod.

Then we need to look at the AC conditions, is the driver doing the required job?

Then back another stage; stable?  Sufficient?

Finally the inputs, and a fully functional amp.

And from that stable foundation you can then tinker and mod with confidence.

HTH

Yes that helps immensely! But.. did you notice the output transistors?
I installed the T03 2N2148's (a few pages/posts back) they don't even get warm.
There is no more (doesn't seem to be) thermal runaway, and so far they seem to be doing ok even with the (probably) less than optimum biasing.
And Q3 and Q4 do not get warm either. Not even a little bit.

For all the rest of your above post...

Thanks! lots of good stuff there and food for thought.

I'm goin' back in swingin'... De-coupling, here I come!  :)

Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 29, 2014, 10:38:18 PM
Hummm, I found a Data sheet for the 2N2148's...

It's a pdf but secured so I can't print it but I think I can link to it...  :)

http://alltransistors.com/pdfview.php?doc=2n2148.pdf&dire=_rca (http://alltransistors.com/pdfview.php?doc=2n2148.pdf&dire=_rca)

Let's see if this works...
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 30, 2014, 12:06:38 AM
Ok, got a little work done.

1. Input jack shorting type
2. C16 now 1000uF
3. Added R13 1K
4. Added C9 1000uf

See schem.

Amp is "better" squeal now starts at @ 8.5 on Vol instead of @ 6.
I have been keeping the Tone on 10 as that makes it the worst.

Squeal happens even with input jack shorted to ground, so it's (obviously) the amp itself oscillating.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 30, 2014, 01:10:54 AM
Just for gits and shiggles I removed C6 10uf emitter bypass cap on Q1.

I know those emitter caps maximize the signal gain of the stage.

Well... squeal is gone tho the amp lost quite a bit of volume.
Also backing the Tone down from 10 even slightly, lowers the volume quite noticeably.
Tone at 0 and the amp is barely heard and quite dull sounding.

For fun I installed a 1uF cap instead of the 10uF.
Squeal came back at 9 on Vol and amp got a bit louder again.

So my initial uneducated (as yet), thoughts... randomly...

1. The squeal originates in Q1, it just has too much gain with the better PS.
2. Q1 is ok, but too much gain overdrives the driver circuit of Q3 and Q4.
3. There is a biasing issue. Somewhere...Everywhere...?
4. The new 2N2148 output transistors bias is wrong.
5. All of the above

Thinking about it... of course lowering the gain of Q1 reduces/eliminates the squeal because turning the Vol down basically attenuates the signal and gets rid of the squeal. "sorta" the same as reducing gain.

The difference is, with C6 installed and volume down the amp is very distorted at all non-squeal settings.
With C6 gone, the amp is mostly clean with just a hint of distortion, even at full volume.
Yes, I know there is a difference between lowering gain (voltage) and attenuation. They are *not* the same thing.

Hmmm, gonna sleep on it now. It's late here and I'm tired.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on August 31, 2014, 05:54:38 AM

Well another thing to consider are grounding paths.  Is there a bottleneck somewhere causing preamp returns and power amp returns to share a small common track or wire (with apparently significant resistance)?

Good grounding is single-point to the chassis (but not the mains safety earth), and radial to each of the sections from there, the sections isolated from chassis ground.  It is likely this amp has been built on the "ground everywhere" scheme, with can work, sorta.  Until somebody goes and bolts on a supercharger...  :-X  ...then moms runabout needs some chassis and suspension work.

This single ground point should also be as close to the south end of the main filter cap as possible, but not share any of its AC paths, and decoupling caps should be at the stages they decouple (the isolating resistors can be anywhere).

So the power feeds and returns should all radiate from the main filter cap; then stages don't have either supply or ground resistances in common, so they are less unintentionally coupled together via the power and ground supply.  :dbtu:

http://www.ozvalveamps.org/grounding.htm (http://www.ozvalveamps.org/grounding.htm)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 31, 2014, 09:54:27 AM

grounding paths

Ahhh Ha Ha Ha ...hahaaa gaspchokesnortcoughwheeze....

Sorry... I just spewed hot coffee out my nose and all over the keyboard....

Yes, grounding paths,,, harrumph...

I actually know about star grounds etc. as I have Kevin O'Connors excellent books the TUT (The Ultimate Tone) Series 1 thru 5.

http://www.londonpower.com/audio-design-books (http://www.londonpower.com/audio-design-books)

He writes extensively on the subject of grounding in tube amps (and other).

Too bad I read stuff without sometimes actually comprehending/understanding/retaining what I'm reading... (embarrassment)
perhaps a touch dyslexic....  :duh

In my defense, it's been a long time since I read those books and I never actually applied anything from them.
Your mention of star grounds triggered my memory. (such as it is)

Anyways... this amps grounds are probably about as random as you can get.
There are 2 sorta "L" shaped ground tracks on the board. Both originally had separate leads to ground.
One to the input jack ground, the other to one of the pots body.
I jumped the 2 tracks together so as to have one ground lead from the board.
The main filter cap ground goes to the speaker jack ground near the PS.
So the chassis is the ground path for *all* other grounds.

I will correct this before I go any further.

Thanks for the link to your site on grounding.  :) Great stuff!

BTW I've been reading (and actually understanding and learning :)) the ESP Basics Articles on Electronics and Amplifiers.
Good stuff, easy to understand.  Learning lots and have been applying what I'm learning on breadboard circuits.  :)

Will report on how the ground issue/correction goes...
Stay tuned!

Oh, also BTW this amp has never had a hum issue, quite quiet actually, so I never considered it to have a ground problem.  :loco
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 31, 2014, 03:15:46 PM
I'm also working on a few things in parallel here...

I do make changes to the amp one at a time.

This is just my latest idea for the 3 inputs.

Normal Input is just a copy of what I already have.
High Input has a gain of 10. I lifted the circuit from an app note somewhere.
Low Input is obvious...

Will this work? Any obvious flaws?
I know the passive mixing of the three 10K resistors is not ideal...
Does the Low Input need a coupling cap?
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 31, 2014, 07:46:39 PM
Alright, I got the ground changes done.

1. Installed an insulated jack for the speaker. Ground of this now goes direct to main filter cap.
2. Short lead from main filter cap to chassis.
3. PS + and - now go directly to the board from main filter cap. Each go to the end of their respective traces near the PA section.
4. All 4 pot grounds now go direct to board near their respective circuitry.
5. Input jack is *not yet* insulated but I ran a jack ground wire all the way back to the main filter cap anyway.
If there is a loop, this is where it will be.
6. Input buffer is still grounded to the input jack. (mounted on it actually)

Test conditions;

C14 and C15 bypass caps on the driver transistors removed. All else just like the schem shows.

When I first fired it up I thought something was wrong, or I had made a mistake somewhere...
It was soooo darn quiet.
If I thought it was quiet before, now it's dang near silent. Barely even any hiss.

Sounds good, clean, low volume, about bedroom level. No squeal. Any settings.

Installed both bypass caps C14 and C15 (not sure how their values affect gain, if at all) used 1uF for C14 and 10uF for C15.

Test;

Squeal is back but character has changed. Due to value change on the caps?
Tone 10, Vol 2, squeal starts and is harsher and nastier than before (more high freq).

Tone 0, Vol 10, No squeal, Thick pleasant distortion. LOUD! Could gig with that sound! :) Crunch Rhythm only, not a good lead sound.
Bring Tone up to 2, squeal starts... nasty nasty nasty.

Next up, insulate input jack, play with C14, C15 values, see what happens...
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on August 31, 2014, 10:14:48 PM
HAH! I killed it!!!!  :dbtu:

No more squeal!!!!

More later....  ;)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on September 01, 2014, 01:28:20 PM
Here are the latest changes.

1. Added insulated input jack, grounded jack on Vol pot.

2. 2N2907A's for Q1, Q3, Q4.

3. For Q1, R6-180K, R7-18K, R9-27 ohm (basically adjusted the bias to have approx 1/2 the supply Voltage on the base)

4. For Q3, R21-5.6K, R22-2K

5. For Q4, R23-1.5K C15-47uF

What killed the squeal was mostly the changes made around Q3 and Q4.
esp. R21-5.6K
I guessed that the original R21-330ohm sets the gain there,
so thought I would attempt to lower the gain.

Stuck a 10K in for R21 and got no squeal but very little volume.
Got out the R substitution box and started trying different values.
4.7K was no squeal but very loud and harsh sound.
5.6k tamed it.

Not sure how all the other changes affect things, but for reference I added the voltages measured around Q3, and 4.
What voltages should we be seeing there?
What would be considered "normal'?
Should I do something with R20-6.8K?

Amp now sounds "OK" fairly loud at Vol 10. "almost" clean at low Volume.
Tone ranges from quite thick to almost ice-pick.
All that can be tweaked as we go...

It's getting there....  :)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on September 01, 2014, 01:51:21 PM
Quote from: galaxiex
Ahhh Ha Ha Ha ...hahaaa gaspchokesnortcoughwheeze....

Sorry... I just spewed hot coffee out my nose and all over the keyboard....

If it hadn't been for Intel and Microsoft we would have had keyboards with detectors and airbags to prevent this sort of thing by now.   ::)


Yep yep, Doug Self, Pat Hawker, Baxandall, the whole Newnes/Wireless World crew.


Quote from: galaxiex
this amp has never had a hum issue

This typically has to do with a shared earth path between a supply rail and the path around the tranny, rectifier, main filter cap.  The "right" place to make supply and return connections to the PSU is at the main filter cap terminals, that way the resistance in common between the charging and discharging paths is limited to the ESR of the filter cap.


Quote from: galaxiex
4. All 4 pot grounds now go direct to board near their respective circuitry.

+1   :dbtu:


Quote from: galaxiex
5. Input jack is *not yet* insulated but I ran a jack ground wire all the way back to the main filter cap anyway.

With an insulated jack you take its earth return to the AC common ground point for the first stage, not back to the central ground point - it then goes there on its specific ground, but first reference the signal to the amplifier ground, not via a long loop back to the single-ground point (it should still be quiet, but...).


Quote from: galaxiex
Installed both bypass caps C14 and C15 (not sure how their values affect gain, if at all) used 1uF for C14 and 10uF for C15.

These control the local AC NFB around the pre-driver and driver stages.  As their values are reduced the low end rolloff comes up in frequency, bass cut.  I'd be inclined not to dick with them for the moment because your f/b sounds like it is mid-hi freq "", n'est pas?  So we need to go looking for a high frequency feedback path we don't want, and apart from common grounds, that can mean unwanted capacitive coupling.  The grounding around the pots doesn't sound too flash, and localising these controls and their grounds would be something I would have been looking at next.  {the old layout isn't up to the new gain, some re-engineering is required, but this continues to be a great learning experience when you start off with a sow's ear and some prospects.  :lmao: }



nope, that cct won't fly.

Now need to mod the input to have a "Half Rail" Vsup/2 provider.  1:1 voltage divider across the local supply, bypass mid point to AC ground, this is now "pseudo-ground" for the op-amps, and they are effectively running from +/-supplies half the whole supply.

This allows simplification of the input biasing, just a single 2M2 to this new half-rail point, and it provides for low-Z gain arrangements.

I've cascaded the gain and buffer stages to avoid the need for an output mixer.





PS
cross posts
good new, yeah the 330 sets the loop AC gain

I wouldn't be content with that 'tho, tamed, but not yet unconditionally stable.

Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on September 01, 2014, 04:01:23 PM
I wouldn't be content with that 'tho, tamed, but not yet unconditionally stable.

Yeah, seems like lotsa tweaking still to do...
If I knew how to use/apply some of the math I've been reading, I'm sure it would go much easier/faster.  ;)

Anyways....

Keeping up to speed here...

1. Input jacks now insulated, and grounded to Vol pot ground. Which goes to board near Q1, not ideal but works.
1a. Existing Input buffer presently grounded on input jack, so, ok.

2. Bypass caps C14, C15 now 10uF and 47uF.
With the 100uF at C15 tooo much bass response, maybe if I played a Bass Guitar. :lmao:
(sows ear heh heh heh  :))

3. New schem of input buffer(s).


--------------------------------------------
Random thought(s), feel free to ignore....

Ever has there been such effort and re-engineering expended on such a (started out as) piece of crap amplifier...
Only a fool or insane dummy would do such...   :duh  :lmao:

The end result (if we ever get there) Is going to be soooooo coooool!  8|

More random thought...

How about a "Fuzz" circuit for J3?
Re-purpose those germanium transistors I pulled off the board. Yeah! Built in Fuzz Face!  :lmao:

Could label the front panel...

1. Normal
2. High
3. Fuzz

Sorry... I can't help it... the Muse is with me and I'm just inspired...

besides... i have this huge (95x47cm) stripboard for mounting the input buffer(s) and reverb brick, (when we get there)
and all this room near the input jacks...

Fun Fun Fun...  :)

Edit; does that R5 1K go to ground, or the half rail?
I drew it to the half rail but thinking it goes to ground...
Oh wait, I figured it out.. corrected schematic...
This look good?

Oops, C7 is backwards.

Is there a convention for an input gain stage like this?
Buffer first then gain? or vise versa? Does it matter?

Yet another question...
Can we safely increase the gain of U1b? As configured its X10, can we go higher?

I have a guitar that I really like, it plays great but has very low output. I don't want to change the p-up's
This is why I keep wanting to add a High gain input to this amp.

For the record, the guitar is a 60's Teisco/Silvertone and I want to keep it "stock"
I'm a small guy and these guitars have a short scale and are very light, easy for me to play.
I don't use it all the time, simply because of the low output.
I know I can stick a pedal in front and get gain that way, but I don't (like to) use pedals much.
My main guitar is one of those Made in Mexico Nashville Tele's, great guitar.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on September 02, 2014, 01:27:50 PM
Quote from: galaxiex
does that R5 1K go to ground, or the half rail?

Half rail.


Quote from: galaxiex
Is there a convention for an input gain stage like this?
Buffer first then gain? or vise versa? Does it matter?


In2 --> x10 --> In1 --> buf -->
Always got the buffer, option of x10


In1 --> buf --> In2 --> x10 -->
Always got the x10, option of the buffer


The second doesn't make sense.


Quote from: galaxiex
Can we safely increase the gain of U1b?

"Safely" in the sense of it catching fire or exploding?  Yes.

"Safely" in the sense of it oscillating like crazy?  Well, mostly.

The Maximum Available Gain is of the order of 100,000 times.  You can probably go up to x100 before it oscillates like crazy (and you should be able to play with one hand only).  Actually attempts at ultra gain like this generally discover that the guitar pickups are slightly microphonic and you start to get "pickup squeal" very like PA mike feedback.  You can't do any harm, so try a few different values and see how far you can push the envelope.


If you follow the x10 amp with a 1k-10k resistor then a pair of silicon diodes (e.g. silicon power or signal, even LED's) in anti-parallel* to ground you should get a pretty effective fuzz.  (*in parallel but opposite directions to each other)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on September 02, 2014, 09:47:28 PM
Half rail.

Got it, I'll fix the schem.

The second doesn't make sense.

Right, I meant in general for other designs...
I haven't looked at enough SS amp schematics to have a grasp on what the "normal" design conventions are for clean and gain channels.

You can probably go up to x100 before it oscillates like crazy.....
.....discover that the guitar pickups are slightly microphonic .......

.......try a few different values and see how far you can push the envelope.

Yep, I've had that from pickups that are not potted, and even some that are....

Ok, I'm guessing R8 10K is the one I increase to up the gain?

Fuzz;
Right, 1 to 10k + diodes to ground, seen that lots.  :)

Another rambling random thought...

Some of this stuff (electronics) is slowly coming back to me.  ;)
Big difference in just copying something out of a book or wherever,
compared to actually understanding what the circuit does and being able to apply it to other stuff.

Edit; I'm getting this wired up right now (sans fuzz circuit) and I noticed something....

Do we still need R7 100K from pin 7 of U1b?

We originally used the 100K on the output of the buffer to get the trem to work.
R7 is not needed for that here.

Now, I can see that with nothing plugged in at all,
it provides a ground path for J1 suppressing any noise from an otherwise open jack.

Correct?

(see, I'm lookin at stuff and trying to understand how it works  :))
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on September 03, 2014, 07:25:43 AM
Quote from: galaxiex
I haven't looked at enough SS amp schematics to have a grasp on what the "normal" design conventions are for clean and gain channels.

There are all sorts of variations, but one way channel switching is done is like this;
Code: [Select]
In --> preamp stage -->Ch sw--> -------------------->Ch sw --> Master
                            --> gain+diode clipper-->
A footswitch drives electronic signal switching which inserts extra gain and a diode clipper in the middle of the preamp.  This is essentially a built-in fuzz box with an electronic (transistor/FET/relay) double pole double throw switch at each end - just a complicated version of stomp switching.


Quote from: galaxiex
Do we still need R7 100K from pin 7 of U1b?

Consider: we have a guitar plugged in to J1 when we switch on.  Without R7 there is no way for C5 to charge up, so its "groundy" end is at half rail with the output of IC1b.

Now you unplug your guitar and the amp input is now suddenly connected to a voltage of V/2 while C5 charges.  "SPLAT!!!".

With R7 C5 charges, so when you pull out your plug the input will switch to "ground volts".  Bit of a click maybe.  This is why you see those "useless" 10 Meg resistors on every audio switch contact to ground - it's to keep all the caps charged and mission-ready for when you change a switch, and they are all charged up to their working voltages ready to go, no ugly splats.

Quote from: galaxiex
Correct?

Correct.   :dbtu:

Note a little feature of your arrangement is that the pre-amp buffered guitar signal is available on J3 as a recording (dry) output.



A few op-amp basics...

The voltage gain of IC1b is the ratio of R5 to R8 (a.k.a. Rshunt and Rfeedback, Rs, Rf)

Voltage gain Av ~= R8/R5 (use for large ratios, high gains)

Av == (R5+R8)/R8 (accurate, use for gains below ~20)

N.B. that this is the same as the voltage divider formula, upside down.

Vout = Vin * R2/(R1+R2)


e.g. "x100"

Rf = 100k, Rs = 1k

(100+1)/1 = 101 - close enuf for audio, only 1% error.

but say now "x3"

intuitive from above, Rf = 3k3, Rs = 1k

(3.3+1)/1 = 4.3 - hummm not even close.

(2.2+1)/1 = 3.2 - better

(1+1+1)/1 = 3 - exact with 2x 1k in series for Rf.


{In a Negative FeedBack path everything is upside down, so an attenuation becomes a gain in the forward path.}

By transposing;

Av == (R5+R8)/R8

... you can find gain, R5 or R8, given the other two.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on September 04, 2014, 12:18:52 AM
Thanks again for all your help Roly. Very much appreciated. Just wanted to say that publicly.  :dbtu:

Got the buffer/gain board done. Works a treat!  :)
X10 gain seems to be plenty for now. (maybe too much, but the rest isn't "quite right" yet...)

Got some other things done too, will update later, for now some pictures....

Excess wire lengths will be trimmed later, got some new pots on order.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on September 04, 2014, 05:10:39 AM
Just went through all the pics.  Man that looks a whole lot better (well the bits you built, anyway).

Mains is safer, PCB add-ins are great.   :dbtu:

One thing, those control leads, no wonder you got instability with all that hair.  Short and Direct is the rule, or screen/shield them.


"Frank-In-The-Box"
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on September 04, 2014, 12:15:21 PM
"Frank-In-The-Box"  :lmao:

I deliberately left the wires long cuz I knew I'd be making changes... I guess that's not really necessary.  :loco
Can change stuff even if wires are the "correct" length and if too short... wires are (relatively) cheap and can be replaced.

I'll correct the lead dress tonight.  :)

BTW that white wire from the buffer to amp is the signal. If I touch it I get a radio station...  :o
I'll definitely shield that one.

I have six colors of wires I use like this...

Red - power + OR -
Black - ground
Green - tone
Blue - trem
White - signal
Yellow - used for speaker out and misc. signal

Output transistor wiring.

Black - base
Red - emitter
Green - collector
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on September 04, 2014, 09:40:24 PM
Better?  ;)  :)

The grey wire from buffer to amp is now shielded.
At full volume not playing I can still faintly hear a radio station....

Was thinking when it's all said and done I will strip the chassis and blast it.
(I have a blast cabinet) and a nice paint or even powder coat?
The original anodizing is stained and discolored on much of it.
If I could find a place local that does anodizing, that might look nicer than paint.
(if not too expensive)
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on September 04, 2014, 10:27:27 PM
Here's the other changes I mentioned a couple posts above...

I followed the values in the data sheet (see pdf attached) for the 2N2148 output transistors.
The data sheet shows with 16.5 Vcc a maximum signal power output of 15 watts.
We have @ 25V on the rail.

But I'm not sure what we have for input impedance of each base.
They show 65 ohms.
Is that the impedance of the 2 transformer coils going to each base?
I'm sure that affects output power.....

Is the above for a split supply where each rail is 16.5V ?

Cuz on the right side at the bottom they show...
"Typical operation in single ended push pull amplifier circuit"
"DC collector supply voltage 16.5V"
Does that mean single supply?

I'll go check the voltages at the output....

I was initially afraid to try those R values as they are much lower than what was there originally.
Decided what the heck and... they work.
Transistors get barely warm. So little that it's hard to tell if they are warming up at all.
Everything else stays cool as well. Transformer too.

Amp is slightly louder and cleaner with those R values installed. (8 ohm speaker for now, when I get the cabinet built, it will be 4 ohm)

Edit; oops forgot to add the gain/buffer to the schem...  :-[
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on September 05, 2014, 12:29:45 PM
Quote from: galaxiex
BTW that white wire from the buffer to amp is the signal. If I touch it I get a radio station...  :o
I'll definitely shield that one.

Not surprising considering there is a diode right at the input - you're half way to a Crystal Set.   :lmao:

Screened lead, ferrite beads, and 100pF cap to ground, all anti-RF.


Quote from: galaxiex
anodizing

I think you will find that coating is "cadmium-passivated" on steel, perhaps better to get it re-electroplated.

Quote from: galaxiex
But I'm not sure what we have for input impedance of each base.
They show 65 ohms.
Is that the impedance of the 2 transformer coils going to each base?

You can't just measure the resistance or impedance of the base of a transistor.  It's effectively a diode to the emitter, and as such has a complex behaviour, acts like a non-linear resistance with applied voltage.  Here it is the current into the base junction that is interesting and (slightly) more tractable.  There is the hope that the upper and lower cells will tend to cancel out any lumpy impedance questions in the driver transformer.  These two drive secondaries are normally wound bifila, meaning wound on together as two twinned strands so they have the best possible matching.

(http://docs.etherkit.com/images/f/f5/Bifilar2.jpg)


Quote from: galaxiex
I was initially afraid to try those R values as they are much lower than what was there originally.
Decided what the heck and... they work.

We are putting a lot more current through the bias divider chain.  This means that the base currents are a much smaller proportion of the whole, so bias voltage regulation is better.

With the lower resistor reduced to 3.9 ohms this reduces the drive source impedance into the base because this resistor is effectively in series with the base drive winding.

"Just warm" is exactly what germanium semiconductors should be when working.  You can just tell it's on.

The voltage across R29 and R30 would be interesting because that will tell us what the idle current through the output transistors is.

Dunno about 4 ohms.  Let's give this a close scrute working out on 8 ohms first.  Just because you now seem to have a good DC condition, there are AC conditions that aren't nearly so friendly, things called SOAR curves, Safe Operating ARea of duration of high current and voltage at the same time into reactive (read real world speakers) loads.


{I would love to have some accurate AC signal voltage measurements at the onset of clip around that driver transformer.  By knowing these we can work out it's turns and impedance ratios, get an idea of what sort of load the driver is working in to on the primary (and so we explore backwards).}


Dead computer PSUs from your local computer shop, all the project cases and hookup wire (in colours) you will ever need.  HV caps and diodes too.   :dbtu:
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on September 07, 2014, 06:12:01 PM
....you're half way to a Crystal Set.

 :lmao:  :lmao:  :lmao:

Yes, I know diodes are great at rectifying RF signals...  ;)

Amplifier stability;
So... a few changes made with stability in mind.
In order of changes made...

1. Put back original R and C values around Q1. Amp sounds good, barely audible hum (I think was always there but so slight I didn't worry about it)

2. Added C26 for RF suppression. Seems good, no more radio station.

3. R24 and C16 (near T2 on schem) are actually physically and electrically close to Q1, Q3, Q4 and T2.

4. Added R41 and C12 down by the trem circuit. This is probably the most dramatic change, so-far as stability goes. Trem still works and is quieter too. No more "thump" "thump" "thump" as it pulses.

But now have hum issue!  :grr

With all controls at 0, no guitar plugged in, amp hums medium loudish...
Start turning Vol up and hum gets quiet-er and at Vol 6 is almost gone, then increases from 6 to 10.
Quite loud at 10.

So I made a mistake when installing C6 1000uf at the buffer supply rail.
Accidentally connected C6 to -25V rail and the junction of R4 and R11 instead of ground.
(I forgot to install C6 at first... :-[ Now don't remember if hum was there before or after installing it wrong)  :-[  :-[  :-[ Rookie mistake!
Turned amp on and was greeted with a VERY loud hum.
Immediately switched off. Possible I damaged U1?
I only have the one TL072 right now, so can't try a new one to see if that's the hum problem.

The hum is quite nasty but if you can ignore it, the amp is actually quite loud and clean sounding (under the hum noise).

Also:
The gain channel may need reducing to X5 gain, as the present X10 is a bit much.

New schem with some voltages added.

Edit;
Hum is the same with or without guitar plugged in.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on September 08, 2014, 03:44:18 AM
I think C25 is supposed to be between the colector and base of Q1.


Quote from: galaxiex
With all controls at 0, no guitar plugged in, amp hums medium loudish...
Start turning Vol up and hum gets quiet-er and at Vol 6 is almost gone, then increases from 6 to 10.
Quite loud at 10.

The volume pot is now sharing a ground return pathway with a fairly high hum current.  In this case it's less likely to be an unintentional ground path so much as excessive current through it due to a fault, say a boofed op-amp.  Finding how hum currents are getting into your signal pathway can sometimes require a bit of detective work.  First get it working again.  Break the signal path to see where it's coming from.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on September 09, 2014, 12:32:28 AM
I think C25 is supposed to be between the colector and base of Q1.

Yep, put it on the board correct, drew it wrong. (smashing head against wall emoticon)

Was going to work on this tonight, but got a box in the mail with the MOD Kits Trill Tremolo diy pedal in it.  :)  8)

So built that instead.  :tu:
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on September 09, 2014, 01:32:32 PM
 :dbtu:
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on September 09, 2014, 02:20:14 PM
Quoted from DIY amp directions >  http://www.ssguitar.com/index.php?topic=3561.15 (http://www.ssguitar.com/index.php?topic=3561.15)

{well it was this or Solitaire   :loco }

Solitare!?!?  Really?!?!?!  ;)

Well... if you are that bored...
wanna design a pre-amp that uses a phase transformer to power stage, negative supply rail, PNP transistors, has reverb (brick), and tremolo, jfet opamp input buffer with gain channel, optimized intermediate stage(s), can be wired on strip board, etc, etc...  ;) ;) ;)

Only need it by 5PM North America Mountain Time today. That's when I'm off work...

 :lmao:  :duh  :lmao:

you a funny guy docta jones....
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on September 10, 2014, 04:07:47 AM
Quoted from DIY amp directions >  http://www.ssguitar.com/index.php?topic=3561.15 (http://www.ssguitar.com/index.php?topic=3561.15)

{well it was this or Solitaire   :loco }

wanna design a pre-amp that uses a phase transformer to power stage, negative supply rail, PNP transistors, has reverb (brick), and tremolo, jfet opamp input buffer with gain channel, optimized intermediate stage(s), can be wired on strip board, etc, etc...  ;) ;) ;)

Nope  8), I've been busy - http://www.ssguitar.com/index.php?topic=3561.msg27099#msg27099 (http://www.ssguitar.com/index.php?topic=3561.msg27099#msg27099) (and on some valve amp design ideas.  To me -32 volts is bias, mmmokay?).
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on September 10, 2014, 08:39:38 AM
Ho-kay,  :)

Nice work on Lauren's Ruby.  :dbtu:
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: Roly on September 10, 2014, 08:56:46 AM
Ho-kay,  :)

Nice work on Lauren's Ruby.  :dbtu:

Wanna knock one up to verify the layout before Lauren starts?   8|
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on September 10, 2014, 09:16:38 AM
Could do.
I probably have all the parts in my junk.
I know I have several 386's.
I might even have that exact board she has.
The more I look at her project and the Ruby, the more I want to build one.
(Drank the Kool-Aid long ago)  ;)

I'll have a look tonight after work, see what I got.
Title: Re: Teisco Checkmate 21 Solid State amp schem + help
Post by: galaxiex on September 13, 2014, 08:50:20 PM
So I'm still gonna fix this amp...  ::)

But I've been busy over in this thread...  :)

http://www.ssguitar.com/index.php?topic=3561.0 (http://www.ssguitar.com/index.php?topic=3561.0)  :tu:

Only enough room on my bench for one project at a time...  ;)