Dunlop Cry Baby 105Q Bass Wah

Unlike the traditional Crybaby, the Dunlop bass wah doesn't use a stompswitch to switch the effect. Instead the pedal is spring-loaded to return to the heel position, where it engages a small momentary switch which bypasses the pedal. You only have to lift a foot off to disengage the pedal, which makes using it for just a few notes much easier (maybe this was thought to be more useful for bass players). The downside is that it can't do cocked-wah sounds without a foot holding it in place.

This one doesn't switch at all, the output signal is always in bypass mode. It does seem to work in that it buffers the input signal, and when power is removed no signal is passed. This is likely to be a problem with the switching system.

The insides are very different to the Crybaby. This is an inductor-less wah, with 2 quad opamps doing the filtering, presumably with a gyrator design. The normal Dunlop Hot Potz is used.

Momentary button desoldered

The switching system uses a small momentary button soldered on to the hidden side of the PCB and poking through the top of the enclosure. One side of the switch looked like it was always closed, so this was replaced with a new one - without fixing the problem. The transistor is just buffering the switching signal, with the new switch installed this could be seen changing from 0 to 9V as the pedal was lifted and dropped, so this part of the PCB is working correctly.

Main board.

All of the rest is done with 4 ICs. The MC33174 opamps are almost certainly doing the filtering, the CD4066 analog switch is routing signals when changing from bypassed to effected modes. The signal from the momentary footswitch is running into a CD4049 buffer. There are some Rs and Cs around the buffer, I would guess it is de-bouncing the switching signal to cut out any popping. There was no activity on any of the CD4049 pins.

4098 buffer desoldered.

I took a picture after I removed U3 but apparently forgot to take one after I soldered a new part. The new chip correctly sent on the switching signals and the pedal wahs once again.

This is a pretty nice design, I only tried it with a guitar as I didn't have a bass around at the time. I would have guessed that the pushbutton is the weak point, but in this case it seems an IC died first.