One of these can help pull knobs with no damage. 

http://www.stewmac.com/Luthier_Tools/Tools_by_Job/Maintenance/Knob_and_Bushing_Puller.html

Could be fabricated with a little ingenuity.

Or the cheaper version... I have this one. It works ok.

http://www.stewmac.com/Luthier_Tools/Tools_by_Job/Maintenance/Knob_Puller.html

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....

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. 

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.

Quote from: Roly on August 07, 2014, 06:13:32 AM

Quote from: galaxiexExpressSCH 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.

Quote from: Roly on August 07, 2014, 06:13:32 AM


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.

Quote from: Roly on August 07, 2014, 06:13:32 AM
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?   

Quote from: Roly on August 07, 2014, 06:13:32 AM
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

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! 

Quote from: Roly on August 06, 2014, 11:57:18 AM

Quote from: galaxiexWhatcha think? 

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

Thanks! 

Quote from: Roly on August 06, 2014, 11:57:18 AM
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.

Quote from: Roly on August 06, 2014, 11:57:18 AM
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.

Well, that didn't take as long as I thought it would.... 

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.

Quote from: Roly on August 05, 2014, 12:22:26 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... 

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.

Quote from: 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

Bakeacake08 thanks for that link. Very concise and makes sense.
Thanks for contributing to my understanding of this. 

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! 

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!

Sorry for the delayed reply...

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

More later... I'm at work right now...

Quote from: 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.

Wow, I even understood all that too.  I can't wait to get home from work to try it! 

Quote from: Roly on July 31, 2014, 09:52:30 AM

Quote from: galaxiexI 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: galaxiexAnyone 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: