Crybaby Classic GCB-95F SMD Capacitor Identification

[william]

I bought a Crybaby Classic a few months ago and finally got around to figuring out what is going on inside it.  I'm thinking I'd like to clone it into a rack system using an LDR and a remote pedal.  I have assumed most of the typical wah values apply for the wah section but I'm unsure how to identify the values of the SMD capacitors around the op-amps.  I cannot make out any identifying numbers on the parts so I'm looking for advice on reasonable values for the capacitors labeled UNK.  There is a section of the PCB dedicated to what I assume is status LEDS for the bypass but they are unpopulated so the actual transistor types and what U2 is is left unknown.  I personally am unconcerned with that part of the circuit but if someone is interested I can post pictures of the section.

[Paul Marossy]

I think you're going to need something that can measure capacitance to be able to figure out that one.

[DiscoVlad]

As far as I'm aware, they're the standard crybaby values - 0.22uF for C8 and C9, and 10nF for C7.

All of the unpopulated pads are because the same board is used for the 535q, 95q, 105q, Dimebag and (unsure about this) Slash wahs. There are schematics for the 535q and Dimebag wahs floating around on either here, or fsb. These should be able to fill in the rest of the missing values.


Edited for wrongness. Oh, you've got a 95F.

[william]

As far as I'm aware, they're the standard crybaby values - 0.22uF for C8 and C9, and 10nF for C7.

All of the unpopulated pads are because the same board is used for the 535q, 95q, 105q, Dimebag and (unsure about this) Slash wahs. There are schematics for the 535q and Dimebag wahs floating around on either here, or fsb. These should be able to fill in the rest of the missing values.

The 535q, 95q, 105q, DB02 and DB01 use different boards than the 95F.  As far as I can tell the 535q and 95q use the same board, the 105q does not use an inductor (I have one), and the DB01 I believe has it's own board.  The DB02 uses a board very similar to the 95F but the additional pads for unpopulated parts that the posted schematic has in the lower left corner are not on the board.  The Cantrell model, Zack Wylde model, and CGB-100 all use the standard crybaby PCB though.  I haven't seen the Slash pcb yet so I can't comment on that one.  I've spent a lot of time looking at Crybaby PCBs the last few weeks.

I have assumed the parts between R18 and C15 all user standard wah values, it is the value of C5, C12, C6, c15, c17, and C16 that I'd like suggestions on.  I'm thinking 0.01uF is a good value for C5 and C6.  but I'm unsure what are good ballpark values are good for the other four.  C1, C11, and C14 are part of the power supply so I'm not currently concerned with their values.

Here are the specific sections of the DB02 and 95f.  You can seen the the lower left section the 95f has additional unpopulated parts in that area.  They are related though in that even the part numbering is nearly identical.

 

[DiscoVlad]

The DB01 uses the same board as the 535q. There are pads for the alternate jack locations, and extra knobs.

I just looked at my 535q, and none of the SMT capacitors have values printed/etched on them, yet the resistors all do. No idea why this is... I guess a pick and place robot doesn't care what values are there, and just loads the board from whatever reels (which do have values printed on them) of parts are loaded in.

[Alman]

Does anybody think that the volume is boosted too much in their Classic GCB-95F? A friend of mine wants to know if I can modify his. I am wondering if it is just his set up or if the wah does in fact boost the wah sound. He hasn't complained much about the bypass signal though. I am studying the schematic at the top of the page to see where I might be able to make a mod. Thanks to William for that.

Al

[Goodrat]

Old post, but I'll give it a shot...
I just got the 95F today.
I noticed that my HSS Strat can distort the signal with the Humbucker on if I bang on a chord.
With a signal gen, I can distort the  circuit if I go over about 200mV RMS. That is what I measure on my guitar if hitting hard.
So I am interested in lowering the gain of the first stage.
My first try will be to lower R2 by paralleling a resistor or changing it (I have a bag of various values).
Let's see, there is a gain of 10 there (I know you have to add one, ignore that) with R2 (47K) divided by R1 (4.7K).
To change the gain to 8.5, R2 should be 40K. I will start there.

Oh, BTW, any clue why my inductor is installed upside down?

Update: Reducing R2 is not enough to get the gain down, even if a short.
It looks like I will need to increase R15 in the emitter of Q1.
I measured a few caps. C5 and C6 are .047uF, C12 is .001 (making that pole 34KHz), C14 0.1uF,
C16 is 15uF. My coil reads 657mH in circuit.
R15 is 470 not 47

Update 2:
R15 works out fine. Increasing to 470 was still too too loud compared to bypass, so I went to 760 which was ok with just a hint of distortion still there if I play the strings hard at certain positions of the wah. Then I tried 1K, which is where I am now. I would guess 850 ohms would be just right. (I just have to find one in my mixed bag of SMD parts).
I'll leave the 1K in for a while. I think there should be a 2K pot there. Hmmm.

Update 3:
I found an 890 ohm. This seems fine now.
Effect volume sounds the same volume as bypass and no distortion crackling with a humbucker with the increase in R15 to an 850-ish value
Success.

[Goodrat]

As usual, I try to re-invent the wheel.
I should have discovered this article:
http://www.geofex.com/article_folders/wahpedl/wahped.htm
I probably should play with the input resistor at Q1

[Goodrat]

Hold on.
I spent some time making my own schematic from the one that was traced in this thread.
As I went to measure some caps, I noticed that my 95F is quite different. I have Rev E.
For example I have a U4 (Some regulator I assume that is marked G111) and I don't have a zener or the 100 ohm off the battery.
Here is a pic:
http://www.rickviola.com/images/GBC95F.JPG

Notice my upside down inductor.
Otherwise, as far as the above trace by William, this is what I have so far, but now I can't verify that rev. and I measured caps in circuit.
So, this is just for conversational purposes and labeled preliminary:
http://www.rickviola.com/images/GBC95FrevB.jpg


Update on the gain thing.
Changing the resistor at the base of Q1 from 47K up to 100K, I notice the gain change, but I still get distortion.
So I will put the emitter resistor back to the 890 change. Probably around 800 would be good, since you want a little bit of gain with the wah so you can hear the lower frequencies a bit more. I think I will widen the Q next by lowering the resister across the inductor.

Schematic notes: By comparing pictures, William's trace and my measurements. I think we have an accurate Rev B schematic. I added missing values and corrected a couple of reference designation errors on mine, plus made it prettier. I have to investigate the extra parts on my Rev E. I made the inductor 650mH because that is what I measure.

[italianguy63]

I have one of those boards laying around here too.  I looked and I have a Rev "D" board.  Looks like yours too.  Even the upside down Fasel.  BTW, does not matter-- only 2 connection points, and the orientation is unimportant.  A good value for "Q" - R17 is 68K.  In the schematic, the "uninstalled option" for points B&C looks to be the Q pot, like on the 535-- maybe an easy add-on if you can get the values.  Should not be too tough.  Agreed, the schematic shown is similar, but not the same.  I want to add a power-on LED to mine.  Let me know if you come across a good point to add one in.  I was looking and thinking maybe the +4.5V point would be good.  MC

[Goodrat]

No, leave the 4.5 bias voltage alone. That needs to be clean. Use 9v, see if 4.7k with the LED is bright enough for you.
But with a wah, know it is on. Plus you have to switch it, because 9v is always on if the input jack is used or using external DC.
Maybe they started installing the inductor upside down to get a small increase in inductance from the cover, or some other issue from nearby components.

[Goodrat]

Someone explain to me why the values of R1 and C12 are what they are.
That calculates to a low freq roll off of 33.8KHz on the input buffer.
I measured that cap as 1nF

[Seljer]

Someone explain to me why the values of R1 and C12 are what they are.
That calculates to a low freq roll off of 33.8KHz on the input buffer.
I measured that cap as 1nF

R1 and C12 with the opamp make a shelving eq stage that gives a high frequency boost. For low frequencies it functions as a simple buffer (think of the cap as infinity ohms as you move towards 0hz), for higher frequencies it gives an amplification of 11x (or 21dB) with a +3dB corner frequency around 3.4kHZ (you have to take into account the gain from the opamp as well when calulating the frequency).
If you look further ahead after the entire wah circuit and another buffer you see a low pass filter made out of R22 and C17 that has a relatively similar corner frequency.

The first stage provides pre-emphasis and R22 and C17 form the de-emphasis filter. They boost the treble ahead of the circuit, so you can then cut the treble after the circuit and get a better signal to noise ratio overall. You may spot the same thing in certain phasers and chorus pedals. This is the basically same principle they apply to vinyl records to get less noise, they cut the audio onto the record with notable treble boost which the preamp then removes on playback.

[Goodrat]

I see it. I was doing a simulation of the input buffer and I was comming back here to say, ohhh!
But I had just calculated the R22 and C17 low pass and wondering about that. It makes sense now.
So, if I think the effect volume is too high, I probably should only play with emitter resistor R15, or better yet, the divider of R23-R24 at the output.
I would like to get the sound less thin though. Interesting. Thanks.

Playing with a simulator more, I see if I leave the HF filters alone and I wanted to not roll of the bass so much, C6 should be raised, to at least .22 up to 1uF.
I'm going to try that.

[Goodrat]

Only problem is, C6 will not have much affect, since the wah circuit takes over the response.
As far as controlling output with R23/24, that is fine for effect volume, but will not cure any over driving distortion of the Wah circuit.
So I put a 2K trimmer in R15.
The value I seem to like when adjusting that is 850 ohms.

http://www.rickviola.com/images/WahGain.JPG

[Goodrat]

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.

[matt239]

So, if I understand what I'm seeing correctly;

C7 can be removed and several caps put on a switch connected at JP1 for a range switch.

R17 can be removed and a pot inserted at TP3 with a resistor at R12 for a variable Q control.

Right?

[matt239]

I could also use some help calculating values for the first op-amp buffer/filter.

I can do the basic resistor-only op-amp gain, and there are online calculators for Sallen-Key filters, & basic Bessel filters,
but there is no calculator or explanation for a setup with only the one cap in this position.
I get the basic concept, but I don't know how to do the calculation.
I'm not an EE, so my filter kung-fu is not strong.

I'd like to reduce the gain to 9dB or 12dB instead of 21dB, and lower the corner frequency to about 1k.

[matt239]

Can any of you help get me pointed in the right direction on calculating values for the first filter?

I know it's basic electronics, and the information is out there, but I'm having a hard time finding what I need in a format I completely understand.

I can do R-C filters, and I can do op-amp gain, but I don't fully understand how to calculate op-amp filters with gain.

There are several calculators for filters online, but this filter is missing a cap to be a typical configuration.
I don't know what to enter for the missing cap; 0? infinity?

[PRR]

> help get me pointed in the right direction

Would help to post a picture of the section that you are asking about.

Also how far you already got. You said you can compute gain, but what did you compute?

I will guess this part:



> I can do the basic resistor-only op-amp gain
> no calculator or explanation for a setup with only the one cap in this position

If you can do the gain, you can estimate what cap WON'T be happy.

All caps are infinite impedance at zero frequency and zero impedance at infinite frequency. In-between they are in-between.

Assume the cap impedance is very-high all across the audio band. What is the gain? You should compute "unity". If so, why have cap or gain-set resistors at all?

Assume the cap impedance is very-low all across the audio band. What is the gain? For 47K+4K7 you should compute "1:11 or 20.8dB".

Assume the cap impedance is "equal" to its series resistor at some frequency. What is the gain? Using simple logic, gain is half. (In fact it is 0.707 because reactances are twisty things.)

If you explore both ways, cap impedance rising and dropping as frequency drops and rises, you can pencil-out the general trend of gain.

So mostly you ask "What frequency makes this cap's reactance similar to this resistance?" I know there are ways to calculate this, online if you must. A Reactance Chart is a handy thing to post on your wall.

You want "9dB or 12dB". What gain-set resistors do you compute?

It is often easier to leave one resistor alone and tinker the other one. Which gain-set resistor should you dink with?

Different situations can go different ways. _I_ think 47K is a mildly high value and would reduce it. 10dB is 3:1 so R2 could be twice R1, 10K. We must check that R2+R1 does not cause excessive load on the opamp. Since most any opamp can drive 2K, we should be good.

Since we have not changed R1, it is likely that we can keep the same C12 value for the same bass limit.

Being a hi-fi-guy, I'd think "1K and 10uFd reaches below 20Hz, full-range. So 5K and 2uFd would also be 20Hz, and 4.7K+2.2uFd is right down there also. Done."

This is not a hi-fi rig. Heavy bass-cut may be needed to prevent muddiness. Another plan here shows 0.001uFd here. If 2uFd is 20Hz, then 0.002uFd is 20KHz. Bottom string (82Hz) is VERY cut-back, response rises ALL up the audio band. Unless the L-C resonator has a complementary slant, this may be a mistake?

> 9dB or 12dB ....lower the corner frequency to about 1k.

I agree. If 2uFd gives about 15Hz, I bet you can work it out.

ALTernatively: clip-leads and a box of capacitors. How do you know 1KHz is optimum? If that's in the Buyer's Specs, the buyer is always right. But if working toward your OWN happiness, 500Hz or 2KHz or 700Hz may ring your chime best. And you don't really need the frequency, or the capacitor value, but the "sound". Try-and-see is a valid design path.