Crybaby Classic GCB-95F SMD Capacitor Identification

[Brymus]

I did more testing today concerning humbuckers over driving the GCB-95F (Rev E) Crybaby at certain positions of the wah pedal.
The easiest solution is to increase R18 (resistor at the input of the Wah section)
from 47K to 100K. With the Q1 base resistor R15 left at stock 470 ohms, this is acceptable to me.
I'll leave the R15 as a trimmer for now.

I just turn my guitar volume down until it doesnt distort (it has treble bleed)
Increasing the 470R up some helps too,I think you mentioned that already.
Perhaps better would be a buffer at the output with a slight gain and an output trimmer pot (volume)
I have been messing with mine I have the same board but replaced it with a moddable through hole board.
I believe the reason for the inductor laying down is parts clearance,as some have the battery drawer in the middle instead of heel area.
Something I overlooked when retro fitting my new board...
A cool mod I did was adding a 100K pot in series with the wah pot on the heel down/bass side you can then select the range of the wah you want to affect and it also removes the nasal sound from bass end of the sweep.
Also switching the red fasal for a transformer inductor removes the nasal bass sound too.
Right now i am trying out different buffers to see what I like best,Then perhaps I will make a new board and note the battery drawer clearance.

[matt239]

Thanks Paul!
You're always so helpful. I truly appreciate it.
Actually I got it just about worked out right before you posted.
- but your comments are still very useful.
I didn't post a picture because I was referring to Goodrat's schematic a few posts above.
I was trying to get rid of some rough distortion in the first transistor, especially at the low end of the pedal's sweep.
I changed the 470R emitter resistor to 1k, then I changed the "Input" series resistor from 47k to 68k.
This removed the low end distortion, but now I could hear some distortion on the top end.

You're right, there's a big treble boost in the first op-amp. - The complimentary cut comes after the resonant circuit, at the output buffers.
I thought it seemed silly to boost the signal too much in the first op-amp, and keep padding it down with larger series resistors, so; - on to calculate values for the first op-amp section!

I figured the gain to be 11x above the knee. I thought like you said, to just change the 47k resistor, and leave the 4.7k alone.
So, I figured change the 47k "R2" to 10k. - Just as you went on to say. And I'm thinking .01uF for "C12"
I have simmed it in TINA and the curve looks about right.

I'm not planning on changing the output filter to match, so some 1kHz boost will remain. I think this should sound good in a wah; a bit more "upper mid-range" bite.
I'll let you guys know how it sounds!

P.S.: I'm considering adding 300pF to 500pF in parallel with R2, around the op-amp. I don't see any point in boosting above 15kHz..
With no input resistor and no NFB cap, seems like this thing could turn into a radio receiver, though I haven't heard any trouble so far; right now it's dead quiet..

[PRR]

> I don't see any point in boosting above 15kHz..
> seems like this thing could turn into a radio receiver

For electrified guitar, I don't see any point going over 5KHz-6KHz. The pickup+cable typically resonate then fall 12dB/oct at/above 3KHz. Guitar speakers typically have sharp top-drops at 6Khz or even 2KHz. And in musical theory, the high overtones (and their IM products!) are non-harmonic; more than a little of that just hurts the ear.

[matt239]

Indeed.
I should have written: boost 15kHz !?! LOL.
My point was that it does boost @ 15kHz, and that's useless, and possibly problematic..

Pretty surprised to see NO series resistor before that op-amp, AND no NFB cap.

Would you bother to add the NFB cap?
- Or not worry about it because the device as a whole is just a big bandpass filter?

[matt239]

And can we add some gain at 2nd transistor without distortion? (Having reduced it so much at the front, pedal is a little less than unity now..)
Say 4.7k instead of the 10k emitter resistor on Q2 (R14) ?

[Brymus]

And can we add some gain at 2nd transistor without distortion? (Having reduced it so much at the front, pedal is a little less than unity now..)
Say 4.7k instead of the 10k emitter resistor on Q2 (R14) ?

Thats why most people make the input resistor smaller or a trim pot so as to set the pedal to unity gain.
You can make the input cap smaller to block some lower frequencies,this will cure your distortion problem without increasing the input resistor.
Then you can set the pedal to unity gain without mucking with the trannies.

[matt239]

Thanks, but have you been reading the thread?        - It's not the standard circuit.

There is already a big treble boost/relative bass cut at the first buffer.
There is no actual input resistor, I've already increased what would normally be the "input" resistor going into Q1, and increased the Q1 emitter resistor, to reduce distortion.

- So I've already cured the low end distortion, now I'm fixing a little distortion at the high end of the sweep. - but it's getting just a touch quiet. - I can't get more gain at Q1 w/o distortion.

There are two buffers after the wah circuit; normally I would recover a little gain there, but they are hardwired via tiny smd-style traces as buffers; there is no component to replace to give them gain.
So: I'm looking for a little more gain from Q2.

(I'm not totally opposed to some distortion in a wah, what people call "growl," but in this case I'm trying to make a clean one..)

----------------------

-- I actually bought this cheap, "as is" - supposedly broken. I was just going to yank out the board and put in a "normal" one (pre-smd..) but it turned out not to be broken at all,
but was not quite dialed-in to my liking, so I set about tweaking it. - Tricky with SMD, but hasn't turned out to be that hard. And I was going to build one with buffers anyway..
______________________________________________________________________________________________

[Brymus]

Yeah I read the thread,I have the exact same one.I got mine broken as well,it was actually broke IDK why,but I didnt feel like mucking with SMD components and I already had a board etched (the old GGG mod wah board) for the last wah shell I got,but I built the prototype UVICS in it instead of a wah.
Just chiming in as you seem to be going through exactly what I went through only I didnt do any sims or math.
I simply pulled the inductor, caps,jacks,and the footswitch and built the other one.
I applaud you for using the stock board ,they are rather nice looking and seem VERY sturdy,and have pads for the more expensive versions of the wah.
Mine (OEM) used SMD op amps for buffers,couldn't you just change the output from a voltage follower to a non inverting amplifier with minimal resistor changes and trace work?
Anyway keep us updated and maybe a final schematic,and maybe I will try re using the OEM PCB. 

[matt239]

  Yes. my plan was to do as you have done, but now I'm working on the board...
I'm up to doing the tiny smd components, but I don't think I want to cut traces.
Perhaps I can get a bit of level by reducing the 4.7k-R22.  In between the final op-amps. Perhaps to 1k. I'd have to change C17 as well to keep the filtering the same.
I should think that will get me there actually..
Goodrat's schematic seems to be good. (Thank you, Goodrat!)

I'll post a list of all my changes, once I reach a stopping point.

I imagine "good" results might be obtained by doing the opposite of what I'm doing; crank it up, and make it growl through it's range..

[matt239]

OK, here's what I have to report:
Success calculating values, and getting a pretty good sound, ultimately failure soldering the smd board.
I have reached a definite point of diminishing return working this board.
I had good success soldering standing resistors and caps where the smd parts were; I did a half dozen of them with no problems,
but I tried to solder R2 a second time and it just wouldn't work.
I had also not done a great job on the first resistor I changed @ R15, and when I tried to fix it I really hosed the board up.
The traces are incredibly small, more so than necessary just because the parts are smd.. and the foil is incredibly thin, less than paper thin.. why?

I think soldering smd by hand can be done, just not with the tools I currently have. I'd need a lower powered iron, or station, and a much smaller tip.
I was almost able to pull it off with a 25W iron, and standard tip, - but not quite.
Oh, well, I'm no worse off than I had planned to be. I had originally planned to replace the board.. -and I've learned a few things..

Anyway, for those brave enough to solder on this board, If you wish to make a cleaner wah, (many folks may prefer it dirtier!) here are my suggestions for values:

Change R15 to 1k
Change R18 to 68k
Change R2 to 10k
Change C12 to .002uF  (I experimented with .01uF, for more high-mids; it was OK, but a bit too far IMO..)
Change R22 to 1k    (-to recover some level we've lost with the other changes. This gets it back to unity, or just a bit better, clean.) (The MC33175 data-sheet says it can drive 600ohm, so no problem.)
Change C17 to .047uF

This gives a nice clean wah sound with pretty hot bridge pickups.
A good foundation to start with, THEN we can do any of the standard mods to the wah part of the circuit!

[matt239]

BTW, why does Q1 distort so easily?
I know there are limits to what can be done with a single transistor stage, but can we wring any more clean gain out of Q1?

[Brymus]

BTW, why does Q1 distort so easily?
I know there are limits to what can be done with a single transistor stage, but can we wring any more clean gain out of Q1?

I have treble bleeds installed on my LP's volume pots.
Turning the volume down cleans up the distortion.
So I am going to say that humbuckers have enough voltage swing to overdrive Q1 into clipping.

[matt239]

Yes, exactly.
But it seems like we should be able to set it up to be clean without just making it super quiet.
We don't need too much gain from it.

I need to understand the circuit a little better.

[Goodrat]

This is my final version of my clean wah mod with plenty of gain and headroom to handle hum buckers.
I am very pleased with the result.

[matt239]

This is my final version of my clean wah mod with plenty of gain and headroom to handle hum buckers.
I am very pleased with the result.

Cool. Mind sharing how you arrived at these values, and what they sound like?

[champ222]

Hi All

i realise i'm resurrecting an old thread, but the info is all here, so it seems silly to start a new one.

I'm currently trying to fix one of these wahs.

Ive notice that C2 and C4 (both 4.7uF according to the schematic above) have been broken off, so the first job is to replace those.

Are these values critical? I have some 4.7uF caps, but there are not electrolytics, so there huge. id have to mount them off board (the surface mount pads have gone, so surgery is required anyway. i do have some 10uF electolytics, and some 3.3uF tantalums which would be easier to fit in.

Thoughts?

Thanks

[champ222]

Update

I put a 10uF in C2, and the 4.7uF Film cap in C4. Now wah-ing as it should