Wah mods

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Thread: Wah mods

  1. #1

    Join Date: Dec 2011
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    Wah mods info

    i've been doing a lot of modding the past few years on my Crybaby & Vox wahs. it's not hard if you know how to solder--the boards are an older style of design, with the components accessible. and the mods can make a big difference in the sound.

    there's lots of info on the net about most of these mods, but not about others. and it's mostly all from the perspective of vintage cats or blues/rock players, not metal dudes.

    so i figured i'd do some posts about it.

    first, True Bypass switching....
    Last edited by _actual time_; 02-17-2012 at 01:17 PM.
    _actual time_ : prog/math/metal/???? on myspace

  2. #2

    Join Date: Dec 2011
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    OK, True Bypass switching:

    there's tons of blather about this all over the net. the short version is, most all older pedal designs use a SPDT (single-pole, double-throw) switch instead of a DPDT (double-pole, double-throw) because the SPDT is cheaper. the way the pedal circuit has to be designed in order to use the SPDT, the pedal circuitry is always connected to the input/your guitar signal. (only the output is switched). that pedal circuitry acts like a capacitor or a super-long guitar cable, bleeding off high end from your tone when the pedal is switched off.

    some of the vintage cats don't care and blues cats can't hear any difference. but for us metal dudes, playing high-gain amps, any loss in the high end is really obvious. and it sucks!

    the solution: replace the SPDT switch with a DPDT, which lets you switch not just the FX output but the input too. so the pedal circuitry is only connected to the input/your guitar signal when the pedal is on. which makes the tone with the pedal off sound the same as if you weren't plugged through any pedals.

    a simplified diagram i made 15 years ago to link on Usenet:

    this mod is super-common. (all Crybaby and Vox wahs up through the late 90s, and most of them now, use the SPDT.) so there's tons of great resources on the net. and the DPDT switches are easy to find these days.

    Crybaby True Bypass: http://stinkfoot.se/archives/546

    Crybaby and Vox 847 True Bypass: http://www.wah-wah.co.uk/bypass.html

    basically, you make a new wire off the board, by cutting a trace or removing some components. you run that new wire and a new ground wire to the new DPDT switch, plus the three wires that were on the old SPDT switch. those links have details and pics of the boards for different years/revisions of Crybaby and Vox wahs.

    this mod also works on many old pedal designs, like MXR phasers. but i never got off my ass to do it on my Phase 100, so i don't have any info on that.

    next i'll write about some tone mods, or maybe adding an LED....
    Last edited by _actual time_; 02-17-2012 at 01:48 PM.

  3. #3

    Join Date: Dec 2011
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    addendum on Crybaby True Bypass...

    if your Crybaby was made after 1990...

    another way to solve the tone-suckage-from-using-SPDT-switch is to use a buffer circuit.

    (your guitar signal is susceptible to this tone suckage because it's a high-impedance signal. if it was low impedance--like if you were using active pickups--then it's immune to this tone suckage.)

    so after 1990, Dunlop started building a buffer circuit into the Crybaby to try to fix this tone suckage. if your Crybaby's board looks sorta like this, it has the buffer circuit:

    so if you have a post-1990 Crybaby, it might sound just fine when bypassed, and no need to mod it for true bypass. do whatever sounds good.

    (i've had one post-1990 Crybaby that sounded fine bypassed and one that sucked tone. i have no idea why they behaved different from each other. )
    Last edited by _actual time_; 02-17-2012 at 02:50 PM.

  4. #4

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    Cool! Thanks for all the first hand information.

    Here's some of the stuff that was posted a couple months back:


  5. #5

    Join Date: Dec 2011
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    Quote Originally Posted by Matt C View Post
    Here's some of the stuff that was posted a couple months back:

    cool. neat stuff. i've done more tweaking with values rather than brands of components, so my blather will be nicely complimentary to that.

  6. #6

    Join Date: Dec 2011
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    the Q resistor

    ok, the Q resistor, aka the vocal mod:

    the wah effect has a resonant peak, that gets swept up and down when you pump the pedal. a resistor controls the Q of that peak--how wide or skinny the peak is. like the Q control on a parametric EQ.

    increasing the resistor makes the peak more narrow. some people say that makes the "wah" sound more like "woh", so they call it the vocal mod.

    the Q resistor is wired in parallel with the inductor (the big round component in the middle of the board), so they are usually next to each other. in this dude's pics from the link in Matt C's thread, it's the 33k one.

    the stock value in the Crybaby and modern Vox wahs is 33k. most mod pages suggest raising it to 68k. apparently some old Clyde McCoy pedals from the 70s had a 100k there.

    i really like it at 56k, in my Crybabys and Vox. 68k is cool too, but it can get a little sharp for me, especially with brighter-sounding wah circuits like the Vox or brighter-sounding brands of inductor like the yellow Fasel. 100K is way bright for me.

    a lot of those 70s wahs seem to sound way brighter than modern ones. i think the brighter sound works better on clean and mid-gain tones, not with high gain tones.

    my fav way to do this mod is using a trim pot, so i can adjust the Q resistor between these different levels. i'll post some more about that after i snap some pics of it installed in my wahs.

  7. #7

    Join Date: Dec 2011
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    using a trim pot as or with the Q resistor:

    my fav way to tweak the Q resistor is using a trim pot, so i can change it between different values. some of the new models of Crybaby have a pot to change the Q, like the 535Q.

    sometimes i use a 100k trim pot in place of the resistor. like in my Vox 847:

    in this shitty pic, you can see the sharpie marks where i marked when the pot is set to 33k, 56k, and 68k, using a voltmeter before i soldered the pot in. all the way up of course = 100k. (using a trim pot as a variable resistor like this, you only use the left and center legs. you can see the right one left unsoldered. that leg also lets me measure the resistance. )

    an even cooler way to do it is to put the trim pot in series with the stock 33k resistor, so that when the trim pot is all the way down at 0, you get the stock 33k, and then the trim pot dials it up from there.

    in my Crybabys, i like to wire a 50k trim pot like that:

    the pot is sharpied at 23k (plus the stock 33k resistor = 56k) and 35k (plus stock = 68K).

    i wire this pot into the board by desoldering one leg of the stock 33k resistor, connecting it to the pot, then soldering the other leg of the pot to one of the many unused extra board holes that most models of the the Crybaby board have, near the inductor.

    (they put these extra holes on the board so that it can accommodate different types of inductor. trace one that connects to the unused point where the other side of the 33k resistor used to be, and solder the other leg of the pot there.)

    so, what should i blather about next--the sweep cap, or the input cap?

  8. #8

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    Totally worthy of being stickied, IMO.

    Great information in here.
    Argbadh - RHLCİ

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