collapse

Author Topic: Teisco Checkmate 21 Solid State amp schem + help  (Read 35041 times)

galaxiex

  • Legendary
  • ******
  • Posts: 515
  • Chip Points: 46
    • View Profile
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #30 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...  ;)
« Last Edit: August 05, 2014, 05:06:47 PM by galaxiex »
Fear leads to Anger, Anger leads to Hate, Hate leads to Suffering.

galaxiex

  • Legendary
  • ******
  • Posts: 515
  • Chip Points: 46
    • View Profile
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #31 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.
« Last Edit: August 06, 2014, 01:17:58 AM by galaxiex »
Fear leads to Anger, Anger leads to Hate, Hate leads to Suffering.

Roly

  • Legendary
  • ******
  • Posts: 2184
  • Chip Points: 288
    • View Profile
    • Australian Valve Amps
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #32 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.
If you say theory and practice don't agree you haven't applied enough theory.

galaxiex

  • Legendary
  • ******
  • Posts: 515
  • Chip Points: 46
    • View Profile
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #33 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.
Fear leads to Anger, Anger leads to Hate, Hate leads to Suffering.

galaxiex

  • Legendary
  • ******
  • Posts: 515
  • Chip Points: 46
    • View Profile
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #34 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!  :)
Fear leads to Anger, Anger leads to Hate, Hate leads to Suffering.

Roly

  • Legendary
  • ******
  • Posts: 2184
  • Chip Points: 288
    • View Profile
    • Australian Valve Amps
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #35 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.



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



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"   ;) }
If you say theory and practice don't agree you haven't applied enough theory.

galaxiex

  • Legendary
  • ******
  • Posts: 515
  • Chip Points: 46
    • View Profile
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #36 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.



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



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
« Last Edit: August 07, 2014, 11:25:16 PM by galaxiex »
Fear leads to Anger, Anger leads to Hate, Hate leads to Suffering.

galaxiex

  • Legendary
  • ******
  • Posts: 515
  • Chip Points: 46
    • View Profile
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #37 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.
« Last Edit: August 08, 2014, 12:05:48 AM by galaxiex »
Fear leads to Anger, Anger leads to Hate, Hate leads to Suffering.

Roly

  • Legendary
  • ******
  • Posts: 2184
  • Chip Points: 288
    • View Profile
    • Australian Valve Amps
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #38 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.
If you say theory and practice don't agree you haven't applied enough theory.

galaxiex

  • Legendary
  • ******
  • Posts: 515
  • Chip Points: 46
    • View Profile
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #39 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....

Fear leads to Anger, Anger leads to Hate, Hate leads to Suffering.

galaxiex

  • Legendary
  • ******
  • Posts: 515
  • Chip Points: 46
    • View Profile
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #40 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/

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.

« Last Edit: August 10, 2014, 07:20:25 PM by galaxiex »
Fear leads to Anger, Anger leads to Hate, Hate leads to Suffering.

galaxiex

  • Legendary
  • ******
  • Posts: 515
  • Chip Points: 46
    • View Profile
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #41 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?
« Last Edit: August 11, 2014, 12:01:05 AM by galaxiex »
Fear leads to Anger, Anger leads to Hate, Hate leads to Suffering.

phatt

  • Legendary
  • ******
  • Posts: 1992
  • Chip Points: 236
    • View Profile
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #42 on: August 11, 2014, 05:27:16 AM »
hi galaxiex,
Check the voltage on power pin 7 of belton brick,, is it Positive?  ???
Phil.

Roly

  • Legendary
  • ******
  • Posts: 2184
  • Chip Points: 288
    • View Profile
    • Australian Valve Amps
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #43 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


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.
If you say theory and practice don't agree you haven't applied enough theory.

galaxiex

  • Legendary
  • ******
  • Posts: 515
  • Chip Points: 46
    • View Profile
Re: Teisco Checkmate 21 Solid State amp schem + help
« Reply #44 on: August 11, 2014, 10:04:35 PM »
Re-read;

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...

« Last Edit: August 11, 2014, 10:09:55 PM by galaxiex »
Fear leads to Anger, Anger leads to Hate, Hate leads to Suffering.

 

* User Controls

 
 
Welcome, Guest. Please login or register.
Did you miss your activation email?

* Recent Posts

Peavey Stereo Chorus 212 by vidmachine
[Today at 06:52:38 PM]


Heathkit TA16 by GlenF
[May 12, 2019, 10:33:44 PM]


Dual or Split supply Audio amps by phatt
[May 07, 2019, 05:11:13 AM]


implementing presets by jon_bondy
[May 05, 2019, 08:53:46 PM]


EBay TDA2050 boards by edvard
[May 04, 2019, 01:01:31 AM]

* Sponsors