EQWHA-2  Reverse Engineered And Pimped
Making A State Of The Art Wah Out Of A Surplus Tinkererīs Object
last update: May 6, 2022

Copyright 2020-2022 by H. Gragger. All Rights Reserved. All information provided herein is destined for educational and D.I.Y. purposes only. Commercial re-sale, distribution or usage of artwork without explicit written permission of the author is strictly prohibited. The original units  with their associated  trade-names are subject to the copyright of the individual copyright owner. The Author is by no means affiliated with any of those companies. References to trade names are made for educational purposes only. By reading the information provided here you agree to the Terms of Use.
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Index

Abstract
Differences And Peculiarities
Modding
Fine Tuning
Fuzz compatibility - Emulating The Behavior of A Colorsound Wah

Verdict
Reference


Abstract

EQWHA modded
Quite a while ago I bought a wah pedal from tubeampdoctor, called the EQWHA-2.

They sell it as non-working, tinkererīs object, but mine does work. It goes quite cheap, it has a reasonably well made case and appears a good foundation for building all sorts of wah pedals.

Mine has a silvery grey matte surface, but I read it was sold in chrome too. I see Ruby Tubes sell it as EQWHA too.
Here you see it with the mods already in place.


I sounds much like the "Jimi" setting on my Clyde Deluxe, which means it is a Cry Baby type.

Incidentally, it uses exactly the voicing cap (10nF) that constitutes a Cry Baby wah.
A look at the innards however did not make me much wiser since they all look the same. Luckily, they have printed component designators onto the PCB, which unluckily do not match any schematic available. So I had to reverse engineer the pedal. Took me a few hours, but indeed it is an almost exact clone of the GCB-95, which by itself goes back to a schematic from the sixties.

Now instead of gutting the pedal, one might as well use it as a foundation for minor changes, since virtually all boutique wahs are based upon this godfather.
Caveat: despite the striking similarities to ubiquitous Cry Baby derivatives this pedal has a shorter throw.
Later added major design changes in green.

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Differences And Peculiarities

As customary, it has an input buffer to palliate tone sucking caused by a permanently attached load. Of course, it is made so true to the original that it even copies the inferior bypass switching using a 1PDT footswitch. Do they never learn from mistakes?

The input buffer is a bit different from the GCB-95 in that it uses a darlington input transistor arrangement made out of two discrete transistors. This seems a bit overdone at first glance, but maybe this is the answer to this conundrum:


"Most popular DIY wahs use BJTs, which have high current noise. They're a fundamentally poor choice for use with guitar pickups; (...)
You can also minimize the BJT current noise by choosing a high gain transistor with a high Ic(max) rating, (...)"

- DIYstompboxes (user merlinb): Minimizing hiss in wah pedals? (posting #6)
https://www.diystompboxes.com/smfforum/index.php?topic=102462.0


... or a darlington?

Most of the vintage schematics have a 1k resistor at the collector of this buffer transistor, which this one does not have.
Although the biasing scheme for this type of buffer is quite basic, it will work perfectly since there is no big signals to be expected (something we cannot guarantee further later down the line).

  • They positioned a 100nF rail decoupling filter cap directly at the input buffer supply node, which is not a bad idea.
  • R9 (at the inductor) sets the bias for Q4, they decided to have 100k there (normally 82k).
  • The power supply is marginally different, an additional filter resistor and an IMHO undersized clamp diode against reverse power (replaced by 1N4007)
  • Nothing is known about the inductor. Maybe upgrading to a boutique inductor improves something.
  • They chose to connect the board to the outside world with an 8-pin connector. This may be proprietary and different from other wahs.
  • Audio and power connectors  are board mounted, which brings down assembly cost. Everybody seems to take this route nowadays. This is another good reason that speaks for modding the existing board, since it is all there.
Actually, this route is being taken because manufacturing can be made cheaper by this measure. I doubt the longevity of a plastic PCB mounted guitar jack versus a metal case mounted unit from yesteryear. Although superficially viewed you may have gained (by saving money), you have actually lost.
  • It turned out later that the board is size compatible to the boards used in Cry Baby units, which allows for a direct swap.
I have "reverse engineered" the PCB and this is the schematic:

download-icon
Download the schematic

This altogether is exactly what is there in a boutique wah, and indeed it sounds like a Cry Baby. Does this mean it sounds like the one Jimi used (allegedly)? Certainly not. Read on.


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Modding

Now we know what does what on the EQWHA-2, we can start optimizing. Virtually all inductor wahs I found are 100% clones of this circuit. Most of them potentially make variable what has been a fixed value originally, thus provide variety that tricks people into believing in some innovation.


"A friend of mine has just bought a XY signature cry baby wah. I have a cry baby original but his XY sounds so much nicer than mine. Is it possible to convert it?"
- Anonymous voice of a musician mislead by targeted disinformation and hype

"As one might expect, there is very little new in electronics, at least in analog circuitry. (...) Sometimes the innovators try to make their transfer of known electronics methodology from one discipline to this one seem revolutionary. The revolution is not actually the technology, but rather its revelation to the rest of the world."
- Kevin OīConnor: The Ultimate Tone Vol 4, Power Press Publishing, Thunder Bay, CN, 2006, p. 4-15f
The potential mods depicted in the following are what I consider essential changes. Things that should have been done right from the start but fell victim to the buck
  • true bypass switching: really a stock 3PDT footswitch bypass scheme should be employed, does the annunciation LED bit into the bargain, relocation of potentially tone-sucking permanent buffering
  • fuzz friendly output buffering changed, see later.
Those are "nice to have" mods.
  • R5 and / or R12: input gain. Changes bass response too. Can be internal or external.
  • R7: "vocal mod" changes the Q of the circuit and makes the effect more pronounced.
    Can be internal or external.
  • R6: "mid range", as it says. Can be internal or external.
  • C8: "voicing", makes some drastic changes to the voicing from bass wah to Shaft and all colors in between. Usually realized with a rotary switch or a 3 position toggle switch. This makes 90% of the "sound" of a particular wah type.
  • wah pot: changing this is not really a "mod", rather a question of preference. And of course, once the pot is worn.
  • Inductor: hmm. Hard to say what people hear as a difference on different inductors.
  • Cantrell mod: a 5k (trim-) pot in series with the ground leg of the wah pot. Adjusts the travel of the wah pot[3]. Other series resistors (pot lug 3) work too.
Input buffering:

Agreed, using a buffer to alleviate bad input switching for the sake of saving a decent footswitch is a ridiculous idea. This may have been plausible 60 years ago when those parts were not available or incredibly pricey.

However, impedance matching is a good idea. As mentioned, the buffer that is there is perfectly fine and transparent, and it only has to be relocated slightly (see pictures below). Read what I have to say about buffering a wah in general in my Clyde Deluxe article.

A fuzz friendly output buffer (i.e. impedance matcher) is then the only major change which I would add to this pedal. The one shown at home-wrecker[1] would be perfectly fit for the job, but I came to dislike n-channel mosfets due to their potentially high noise levels.
In my rumble box I found a neat j-fet buffer which serves the purpose well. Output impedance is accomplished by a 10k series resistor. This will satisfy all vintage fuzzes. Note: as of May 2022 this has been amended. See below.

Them Changes:

changes
                          to the pcb, top
Changes to the PCB (click enlarge):

On my PCB, I removed all those notoriously tweaked resistors and caps and solder posts onto the board instead, so that I can tweak them with top- or remote mounted components, without having to ever access the bottom of the board again.

As depicted, voicing cap, vocal range (=Q) and mid range are prepared for external access. I added a bass/gain pot lateron, since I felt it needed more body.                     
changes to the pcb, bottom
Changes to the PCB (click enlarge):

On the bottom you see additional supply leads for the external output buffer board. Note the cut trace that permanently connects the wah input to the input jack. Now, it connects to the 3pdt footswitch only,  while the orange wire provides a return path going into the buffer.

The original input buffer is thus always in front of the wah circuit, but the whole electronics is bypassed in bypass mode, as is customary today.
                         
wah
                          inside changes
Inside peek (click enlarge):
  • Top left: 3pdt retrofit full bypass switch
  • Bottom left: (wrapped) simple buffer with output impedance ("imp").
  • voice toggle switch (center off): toggles between stock 10nf (cry baby) 22nf (Zakk Wylde/JH-1) and 15 nF in between mode.
  • Q, Mid and Bass pots, note the mark that designates original values
  • LED, with inline dropper resistor.
see[2] how to do all this, particularly how to prepare the pots.

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Fine Tuning

In my article on modifying the Clyde Deluxe I explain problems that are specifically intertwined with fuzzes and the like. 
There is a trade-off between a fat tone that sounds great clean and a slimmer tone that works better with subsequent fuzzes. This has been covered in the chapter on the Colorsound.

You can consider the changes depicted hereafter non essential. Be prepared to meet a lot of subjectiveness, controversy, voodoo and humor.

The first controversy you meet here originates in the fact that some of the information I gathered from others had to be amended in the lights of setting the wah up like a Colorsound wah.

The stock voicing is rather slim, and it seems that most pedals are deliberately voiced this way to make them compatible for subsequent distortion. As a matter of fact, as an intermediate solution I ended up leaving the trimpots set not very far from the original positions, i.e. with comparable mid range, bias and "voice" resistors.

As mentioned in the other article there is some basic shrillness that I could successfully tame with a 15 nF cap right after the 10 kOhm impedance simulation resistor (part of the added output buffer). This works a treat. See later down why I removed it again for a special purpose.

Bajaman[4] thinks that solely upgrading some of the caps helps tone a lot. Well Iīm usually not into component mojo and this stresses my credulity a lot, but Bajaman is reputable and insists on this; since the change costs almost nothing, letīs try it.
  • I changed C7 (4.7 ĩF electrolytic) into 3.3 + 0.820 ĩF both MKP
  • and also C6 and C9 (although the original ones did not look terribly inferior)

Those were some of the observations that people made:


"I soldered some wires to the 4.7uf and ran them to my breadboard. I added 1uf - no difference, 2uf - no difference (...) Raising the value did nothing for mine."
- FSB (user Bside2234): Dunlop - Cry Baby GCB-95: how to improve it for cheap
https://www.freestompboxes.org/viewtopic.php?t=286&start=100

"No wonder....
changing this cap only results in an illusion for cork sniffers..."

- FSB (user analogguru): Dunlop - Cry Baby GCB-95: how to improve it for cheap
https://www.freestompboxes.org/viewtopic.php?t=286&start=100

So much for that... Make your own decision.

Several forum discussions over at DIYstompboxes rose the issue that nowadays they are using the wrong transistors (mainly too high a hfe) and that different transistors can make an improvement towards a vintage tone.

Wah transistor Q2 (or Q4 in this schematic) is just a buffer, so its influence is negligible, but Q1 (resp. Q3) may indeed do something.


"The only transistor that has a big impact on the sound is the one that has its collector connected to the inductor... usually drawn to the left of the inductor. The other transistor(s) will be buffers and much less important to the sound."
- TGP (user amz-fx [Jack Orman]): Wah Builders/Modders Help (Transistors) [post #9]
https://www.thegearpage.net/board/index.php?threads/wah-builders-modders-help-transistors.1273288/


"It is very human to say "I changed the transistor from Brand X to Brand Y, and it sounded better; (...)

(...) the other stuff around the transistor has a huge effect. Tweaking those parts can make big differences in the sound, probably bigger than changing transistors.  Transistors give you a bag of possibilities. The rest of the circuit gives you the realization of those possibilities. "

- DIYstompboxes (user R.G. [Keen]): Whats a good transister to use for wahs [post #6]
https://www.diystompboxes.com/smfforum/index.php?topic=94107.0

The upshot was that most any transistor would work with a gain around 400. Prepared for some swapping, I installed sockets, but BC549C (being the successor of BC109) in both positions, with a hfe of around 400, sounded so fine that I did not investigate further. Incidentally, those are very low noise too and the total noise level of the pedal is noticeably lower than that of the Clyde despite the compound darlington at the front (the Clyde also catches hum somehow).

I cannot comment on whether the component swap changes tone dramatically, for this I would need to A/B-compare them directly, but the twiddling overall made a perceivable difference. I donīt know if bajaman was serious about that. However...


"I started with buying the Whipple inductor (...)
When I got it I hooked it up to an otherwise stock crybaby and put a switch to change between the stock inductor and the Whipple. I heard absolutely NO difference. (...)
I don't think that the inductor has a huge affect on the tone. The biggest difference I noticed was changing the sweep cap. (...)
My advice for people modding this pedal for the first time: Try all the CHEAP mods first!"

- FSB (user CHEEZOR): Dunlop - Cry Baby GCB-95: how to improve it for cheap
https://www.freestompboxes.org/viewtopic.php?t=286&start=120


"My experience, too. The sweep cap has the biggest affect on things, IMO. (...)
I think in the older wahs the variability between components in terms of tolerances affects the tone the most. For some of them, everything comes together, and for others it just doesn't."

- FSB (user Paul Marossy): Dunlop - Cry Baby GCB-95: how to improve it for cheap
https://www.freestompboxes.org/viewtopic.php?t=286&start=120


"The standard Dunlop inductor isn't bad IMO. There's far more to be had by tweaking everything else."
- DIYstompboxes (user Paul Marossy): Whats a good transister to use for wahs [post #9]
https://www.diystompboxes.com/smfforum/index.php?topic=94107.0

Which of the mods worked? Hard to say. There appears to be a lot of mojo involved and wanna-hear. But since those changes donīt cost an arm and a leg, do them.

My advice for people modding this pedal for the first time:
Try all the CHEAP mods first! - CHEESOR


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Fuzz Compatibility - Emulating The Behavior of A Colorsound Wah

This whole quest started when I combined wah and fuzz. All of my wahs sound great for Shaft. But the fuzz - nothing but fuss. Fuzz into wah and your wah carves out of the sonic spectrum of what I consider elementary for a fuzz, wah into fuzz defeats the wah sweep. Neither of my wahs drives a fuzz well out of the box. It is a matter of - hmm, what? Something is different, because it has been heared.

Listening to Bob Gjika[5], who plays a wah into a fuzz and sounds perfect, you hear the whole sweep of the wah. He says his is a vintage wah. So what about all this vintage sermon?

What the hell is the difference? I tried germanium, silicon, buffered, non buffered - all the same.  The fuzz has hiccups during certain regions of the wah sweep. It swallows up the wah. I suspected too energetic peaks, i.e. too high of Q.

A friend of mine has a Colorsound Wah Fuzz[6]. I have read those are inductorless and I guessed those may be the perfect candidates for what I want. Ibanez' WH10 is inductorless too and seems to work perfect (by the way, the next candidate for a EQWHA shell...). I plugged the Colorsound in and was flattened.

The Colorsound fuzz-wah works perfectly in front of a fuzz.
Its whole sweep is very articulate.
And it is an inductor wha exactly like all others.


Note: usual buffering caveats resp. incompatibilities apply.
A look at the innards reveals to my astonishment that it uses an inductor. A look at the schematic is even more astounding because  both are essentially the same on first glance.

Ah, but that's not quite true. Those are the differences:

(designators refer to a standard 2-transistor wah schematic to make it easier to compare, i.e. Q1 and Q2):
  1. 1k collector resistor: Q2 in contemporary wahs has 1k in the collector line. This one has no resistor (collector goes straight to supply). 
  2. Q1 emitter resistor: modern wahs have a resistor (or resistor/pot combination) there to bring down the gain of Q1.
    This one here is hard wired to ground.
  3. Q limiting resistor in parallel to the inductor: There is no resistor in this circuit unlike in modern wahs (100k, 33k etc.). So astonishing as it may be, the Q will be higher than proposed.
  4. MID resistor: this is the same.
  5. Cbp (electrolytic at the inductor): appears as 4.7ĩF or 10ĩF on different schematics. Value on this particular specimen ist not readable without unsoldering.

ad 1) I temporarily bridged Q2's collector resistor in my wahs and it makes no audible difference. Q2 is a buffer and the collector resistor to my understanding drops its gain slightly in modern wahs. A drop below 3dB will not be perceived. Being a buffer without gain, logic dictates that its influence by matters of hfe can be safely ignored. I use a low noise BC550, but the one there may have done its duty without detriment. I left the bridge in place, so the collector resistor remains shortend.

ad 2) Different for Q1. This is a clear indication that Q1's hfe is important.

Similarly to designers trying to counteract too high hfe's in modern fuzz faces by inserting an emitter resistor, they obviously have a problem with the darlingtons they tend to use in wahs nowadays, so they play the same trick. This unit stems from the 70ies, where gains much below today's values and they had to rely upon maximum gain without local feedback. Borrowing from  the experience with fuzz units, transistors with naturally low hfe's sound better, being able to use the full headroom without constriction.
The transistors there are ZTX109C, which deceiptively sounds like BC109C. The cross-reference lists BC349B 2N3904 as replacement types. BC349 again can be replaced by BC548. Not for the gain, but definitely the same family.

I installed a medium gain transistor in Q1's place, having recently made good experience with MPSA06 (gain of 170).
With the gain pot installed
[2], I dialed in the minimum resistance (full clockwise).


The advantage of using a lower gain transistor is that you can wind the circuit's amplification right up by decreasing or defeating the emitter resistor. Since this is interlinked to bass response, it will also stop bass loss.
Going any lower in hfe such as 70 for a 2N2369A makes the tone mellower, but lacks the growl in the bass range.

ad 3) With the Q pot installed, I dialed in the maximum value of 100k and left it that way. On the scope, the EQWHA has much higher voltage overshoot, so leaving this value in place seems in order.

ad 5) I tried 10ĩ, makes no difference at all. Thumbs up analogguru for cork sniffing.

The major difference the Colorsound makes is the unbelievable range of high to low tones caused by the long pot throw. This is only possibly courtesy of their proprietary pot mechanism. With the EQWHA's pot given you are pretty stuck. Since the treble side is needed for the wah effect to remain audible if driving a fuzz, this is the winner naturally. However, the bass is decent, albeit not as profound as with the Colorsound. You can choose to optimize for the trebly side, or the bassy side.

In order to make a decision, we have to speak about the dreaded conundrum fuzz > wah or wah > fuzz first. The subsequent device always has a dominant role because its peculiar method of frequency filtering swamps everything that comes before. Consequently, you want an ear-friendly, behaved type of wah effect in the first case and (as it turned out) a very different type of wah in the second case.

The same amount of treble peaking that would for a clean signal be felt as shrill is in front of a fuzz absolutely necessary to identify the wah sweep. On the other hand, generating too much of midrange is absolutely counterproductive before the fuzz.

So you can optimize your wah midrange growl with pleasing highs for a clean funk wah, but the same wah would hardly be audible if followed by a fuzz. Reversely, a wah optimized for funk would probably swamp everything coming from a fuzz. I donīt see how this all could possibly be covered by one single (vintage oriented ) unit without driving you mad over complicated switching schemes.

Note that the bass range is somewhat linked to the gain pot. Donīt wind up the gain if you already have high gain transistors.

Optimizing a wah for a certain style
Mode
Mid Treble
Clean Wah (Funk)
meaty (turn mid pot up)
subdued (output cap)
Distorted Wah I (wah > fuzz) to taste subdued (output cap)
Distorted Wah II (fuzz > wah)
be careful (leave as is)
high (remove output cap)

Further measures were:

  • Gear change: I squeezed the last tooth out of the gears towards the trebly side. Accordingly, the bassy side drops behind compared to the Colorsound due to the missing sweep range.
  • It appeared that the (retrofit) buffer was not fit for the huge Q I set. Either it clipped or the wah was not happy without a load. I replaced it by a 22k series resistor as a first aid. The resulting tone was mellower and cleaner overall and should serve the tiredest fuzz well until further advice.
  • I also removed the anti-shrillness cap I had added earlier to restore the toe-down treble (that was in clean mode perceived as ear-piercing). This complements the Colorwah's response nicely and serves the fuzz.
  • It also turns out that the 10nF tone cap, which influences the wah pot sweep, could be improved towards the high side by using 8.2nF instead (for comparison, the Clyde Deluxe uses 15nF, 10nF, and 6.8nF). This complements the built-in pot's law better for fuzz. This way all three switch positions are eminently usable.
  • For mids, I pretty much recommend staying with the original setting. Going below and tone starts to sound anemic, go above and tone gets honky quickly. I ended up slightly above standard.
  • I found the EQWHA's bass fundament a bit weaker than the Colorsound's. I updated the wah part input cap C5 from 10nF to 100nF and now they are similar.
  • By maximizing Q1's gain the overall loudness is increased. Note that in the original schematic[6] there is a 2:1 divider on the output. I installed a similar thing on the EQWHA. 22k:33k worked best.
Note that a resistor in series with the output would probably eliminate all problems with driving stock fuzzes into the bargain. The Colorsound came fuzz-ready!

This exercise teaches us why one vintage style inductor wah can sound great before a fuzz and the other gruesome.


And by the way... this superior sounding wah is full of the cheapest, meanest carbon resistors, film capacitors and electrolytics...
None of that component mojo mumbo-jumbo. How about that?

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Verdict

So how does it sound?
Well at the bottom line - great. Full and fat bottom, tame high end. No longer.
Compatible with everything impedance wise. Fuzz friendly even for stock Germanium units.

It is optimized for wah>fuzz usage and works nearly as good as the Colorsound for this purpose.
Does this all mean, that a such prepared wah is unusable for clean, funky sounds? Absolutely not. But be prepared that it is very bright and very untamed. It thus may easily overpower a subsequent effect or the amp and produce clipping. It also may hurt your ears. Just as the Colorsound. Safety precaution: use a fuzz afterwards.


The Colorsound Wah is like a wild horse, impulsive and difficult to tame.
She is potentially socially incompatible, but she loves fuzz.

So is the EQWHA now.
With the voicing switch you can dial in anything from bass wah to JH-1Zakk Wylde to Shaft. Ironically, this has always been just a question of a single capacitor, cheap to boot.

Is it a great wah?

I donīt know, but it certainly is no less good sounding and useful than its competitor.
The pot sweep is different, but eminently usable.
Maybe they use a different law, but it looks very sturdy.

Yes, being optimized for its purpose into fuzz and lacking a better option, yes.

And the case and mechanics are very robust. Not welded steel like my Clyde Deluxe, but not cheesy plastic either. Its electronics has some little aspects incorporated that creates the impression of being well thought about. Thumbs up for that!

It has a shorter pedal throw compared to a Crybaby despite borrowing heavily from it. You probably need the correct replacement pot, sold as "Ruby pot". PCB screw mount and jacks seem 100% compatible.

I refrain from making sound demos. There is nothing new under the sun.

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Reference

[1]
Home Wrecker: wah mods: http://www.home-wrecker.com/wahmods.html
[2] Andreas Möller (Stinkfoot): diverse excellent wah modding articles in one placehttp://stinkfoot.se
[3] Zakk and jerry wahs, https://www.diystompboxes.com/smfforum/index.php?topic=91315.0
[4] FSB (bajaman): Dunlop - Cry Baby GCB-95: how to improve it for cheap,
    https://www.freestompboxes.org/viewtopic.php?t=286/index.php?topic=91315.0

[5] Bob Gjika: Amp Tone Talk/Demo - Jimi Hendrix Trio Guitar Pedals - Univibe, FuzzFace, Vox Wah - Pedalboard,
     https://www.youtube.com/watch?app=desktop&v=viMmsxzykTA

[6] Colorsound wah-fuzz schematic: http://www.retrotone.com/assets/images/cs/SolaSoundWFS.jpg

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Update History
  • May 6, 2022  section on Colorsound Fuzz-Wah
  • Apr. 24, 2022  section on fine tuning
  • Feb. 29, 2020  first release
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