Crybaby sweep range mod revisited

Overview

Several years ago I modified my Dunlop GCB-95 Crybaby wah pedal to add a second sweep range. The modification turned out pretty well, but I've been wanting more versatility lately. If two sweep ranges are better than one, then six should be even better than two, right? I figured I might as well make a few other changes while I had the wah open again, too.

I based my changes on the modifications described at General Guitar Gadgets (note: the page describing wah modifications has disappeared as of March 2011).

Original schematic

Crybaby Schematic

Note that there are multiple versions of the Crybaby circuit. My wah uses a 3 transistor circuit that adds an input buffer to the schematic shown above, but the rest of the circuit is the same.

Details

• Sweep range - The .01μF capacitor in the lower right hand corner of the schematic is partially responsible for setting the Q factor and center frequency of the filter circuit. I replaced it with a 1P6D rotary switch allowing me to select six different sweep ranges. The values I chose for the capacitors were 5.6nF, 8.2nF, 10nF, 16.4nF, 22nF, and 33nF. These values give a nice broad range of choices, and I could see all of the being useful depending on the style of music.
• Gain - The 68k input resistor can be adjusted to change the overall gain of the circuit. I replaced it with a 50k pot in series with a 10k resistor, which offers a maximum of about 6dB overall gain. Note that this is on my 3-transistor wah. Reducing the input resistor on a 2-transistor circuit like the one drawn above will reduce the input impedance on the circuit. If your guitar is directly connected to the wah, you will not get the full 6dB gain boost, and the highs will be rolled off somewhat.
• Q factor - The 33k resistor is partially responsible for setting the Q-factor of the wah's bandpass filter. Increasing this value will increase the Q, lending the wah a more vocal-like effect. Note that while this action is clearly visible on a scope, the effect in subtle in practice. I initially replaced the 33k with a 22k resistor in series with a 50k pot. Wanting more effect, I swapped a 100k pot in, but it didn't seem to make any difference. The maximum Q is probably dependent on other circuit components, and continuing to increase the resistance probably does nothing beyond a certain point. I may try disconnecting the resistor entirely at some point.
• Saturation - The 1.5k resistor controls feedback from the filter stage. Inreasing this changes how much filtered vs unfilter sound come out of the wah. In effect, it adjusts how much "effect" you hear. I replaced this with a 5k pot, and I've found I prefer a little more "saturation" than stock.
• Filter Gain - The 470 Ohm resistor sets the gain of the amplification stage -- reducing it increases the gain. Unlike the 68k resistor, massive amounts of gain are available -- more than enough to push the transistor into clipping. I replaced this with a 1k center detented pot, and I leave it centered for clean work. The extra gain and nasty-sounding clipping could be useful for all-out heavy metal solos, though, and I'm going to experiment with the one of these days.

Results

Below are pictures of what the wah looks like now:

Overall this was a worthwhile experiment. I like all the adjustability it offers, even if some of the controls are interactive and not overly intuitive. I can easily go from a very funky 70's style clean wah sound to a deep, a saturated heavy metal sound, and just about anything in between.