Dunlop GCB-95 "FatWah" Mod
By Paul Marossy
Last Updated 09/09/05
This is a mod to the Dunlop GCB-95 CryBaby wah pedal that was devised by Paul Crowther of Crowther Audio, maker of boutique guitar effects such as the "Hotcake" and the "Prunes and Custard". It's a really simple mod and it sounds pretty good, too. It only took me 20 minutes to perform this mod and it involves lifting one end of two components on the PCB and adding three new components (four if you add the "fatwah bypass switch"). It makes the wah sound fatter and smoother, it seems by taming some of the piercing highs and emphasizing the mids/lows a little more. It also seems to make it sound a little more vocal as well. This is accomplished by adding a bypass cap on the emitter of the input buffer transistor, relocating the point of connection of the negative terminal of the 4.7uF cap near the inductor and adding a couple of new resistors.
Here is the basic GCB-95 CryBaby circuit. The transistor labeled "MPSA13" is the transistor for the input buffer. We will be lifting the ground end of the 10K resistor on the emitter of this transistor and the 4.7uF cap near the 500mH inductor.
The "FatWah" modifications to the GCB-95 circuit are shown in orange. Simply lift the ground end of the 10K resistor (marked R14 on the PCB) at the input transistor labeled "Q3" and connect it to the new 330 ohm resistor and the positive terminal of the new 10uF capacitor. Lift the ground end of the 4.7uF cap near the inductor (marked C3 on the PCB) and connect it to the new 100K resistor to ground along with the negative terminal of the new 10uF cap and you are done. The bypass switch is optional - I like the sound of the circuit with this mod so I didn't put one in.
This is what my modified GCB-95 PCB looks like. I used a new axial type 4.7uF cap to make connecting everything together simpler. Here's a few different views.
If you looking for a wah mod to try, this one may interest you. It's very simple to perform and and it also quite
easily reversible.