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EQWHA-2
Reverse Engineered And Pimped Making A State Of The Art Wah Out Of A Surplus Tinkerer´s 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  AbstractDifferences And
PeculiaritiesModdingFine
Tuning Fuzz
compatibility - Emulating The Behavior of A
Colorsound WahVerdictReferenceAbstract
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. Back To Index 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:
... 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).
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.
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. Back To Index 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.
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:
Back To Index 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. Bajaman[4] thinks that solely upgrading some of the caps helps tone a lot. Well I´m 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, let´s try it.
Those were some of the
observations that people made:
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
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 don´t know if bajaman was serious about that. However...
Which of the mods worked? Hard to say. There appears to be a lot of mojo involved and wanna-hear. But since those changes don´t cost an arm and a leg, do them. Back To Index 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.
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:
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. I
installed a
medium gain
transistor in
Q1's place,
having
recently made
good
experience
with MPSA06
(gain of 170). 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 10µ,
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 don´t
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. Don´t wind up the gain if you already have high gain transistors.
Further
measures were:
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.
Verdict
I refrain from
making sound demos. There is nothing new
under the sun.So how does it sound?
Is it a great wah? 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. Back To Index [1] Home Wrecker: wah mods: http://www.home-wrecker.com/wahmods.html [2] Andreas Möller (Stinkfoot): diverse excellent wah modding articles in one place, http://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 Back To Index Update History
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