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capacitor mod for wahs

3/18/1998 2:49 PM
allen capacitor mod for wahs
what was the capacitor mod for getting a deeper and fatter wah sound? I saw it here once but forgot to write it down.
3/18/1998 7:01 PM
chip (hys)

try a rotary switch on the .01uf cap from the Q-2's emitter with different cap values Jason liked .02uf the best also the 510 ohm (vox) or 470ohm (crybaby) resitor on q-1's emitter can be changed to a 1k pot Thank RG Keen for all this as he is the mastermind here, also on the fulltone site has a true-bypass layout for the vox that even I understand hehehe cool stuff chip stephens HYS
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3/21/1998 9:16 AM

You can also put caps in parallel with the 33K resistor for the same type sound change, Ben  
PS the .01 here sounds really good. Would this be mathematically equivalent to the .02 from the q2's emitter?? I don't know how to do the math, RG Jack????
3/21/1998 9:20 AM
R.G., How about a GEO page on wah pedal mods. I find all your work very helpful, and it'd be great to have access to a definitive tome on the subject!
3/21/1998 5:44 PM
John Greene
The capacitor connected between Q2's emitter and the inductor determines the corner frequency of the high-pass filter it forms with the inductor.  
There are a few things that are occuring in a Wah circuit. First is the input circuit forms a highpass filter.  
The capcitor and inductor also form a highpass filter, but because they are in the feedback path, it becomes a lowpass filter. The corner frequency of this filter is usually just above the corner frequency of the filter formed by the input capacitors. This leaves a very narrow bandpass filter when the wah is fully engaged.  
The capacitor connected in series with the inductor is more than just AC ground. It forms a series trap with the inductor at a frequency just below the corner frequency of the input filter. This insures that the slope of the feedback filter is really sharp so it doesn't affect the frequencies the input filter is allowing through.  
It also causes the gain to go up slightly in this area causing an increase in gain when the wah is fully engaged.  
The resistors in parallel with the inductor limit the Q of the circuit. If you parallel the inductor with a capacitor you will be adding some bandpass characteristics to the feedback circuit. The point at which this capacitor and inductor resonate (1/(2*PI*SQR(L*C)) the circuit will have maximum impedance which will allow maximum signal to be fedback to the input. In otherwords, this will cause the wah to start behaving like a notch filter.  
3/28/1998 2:37 PM
Just snagged a Morley Vol/Waw, any ideas on where to drop in the prescription? I haven't yet seen a schematic but there has got to be some wild potential for this already groovy sounding unit; but a littly honky unfortunately. Thanks for the advise and the lesson, I just lament practicing in lieu of soldering. Later...
3/28/1998 9:54 PM
Steve A.

    Does Morley still use the light/photo cell(photoresistor?) arrangement instead of a pot? If so I believe that their circuit is entirely different from the basic Crybaby design, so it would require its own set of tweaks.  
    Does anyone know where Morley schematics might be available on-line?  
Steve Ahola
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