Fattening the Tone in a Vintage Vox Wah Pedal
By Paul Marossy
Last Updated 01/28/06
I find the tone of many 70s Italian manufactured Vox wah pedals to be somewhat thin and nasally. The particular one that I have has the original Fasel inductor, and it sounds nice, but I felt that it could have a much fatter sound. Thus began my quest to make it a killer sounding wah. Since this is not an original Clyde McCoy, I have no qualms about replacing a few parts to make it sound more to my liking. One thing to note is that these old PCBs are pretty easy to damage when desoldering components, so be careful!
The first thing that I tried was replacing the original Arco caps with some tropical fish caps. The
results of that mod were inconclusive, but I think it improved the sound slightly. Still not satisfied
that it couldn't be improved more, I tried some other things. I had already true bypassed it, but there was a
little bit of a volume drop when the wah was engaged. Rather than replacing the input resistor, I added a
200K trimpot in parallel with the 68K input resistor to help with that. A measured resistance of 47K seems to
be about the best setting and gave it the best tone.
The transistors do play some role in the overall sound, so I replaced both the FGT102 transistor on the input
and the SIP5172 transistor with some BC109 transistors, and that was an improvement. But still not quite
fat sounding enough.
Remembering some of the things I did when I modded my GCB-95, I surmised that the 660 ohm resistor on the
emitter of the input transistor needed to be lowered. I tried a 330 ohm resistor first and that gave it the
full sound that I was looking for. That one resistor seems to have have the biggest impact on the sound of all
the things that I replaced! It's kind of odd that there was a 660 ohm resistor here as it would
normally be a 390 ohm resistor. In the picture below, this resistor is the one directly below the 4uF cap.
Lowering the value of this resistor will let more mids and lows through.
With a little bit of patience, I now have a fine sounding wah that sounds about as good as the best ones I
have heard. All during this process, I had to find the best setting of the pot's rotation in conjunction with
the mods I performed. Hopefully, this page will give you some ideas on how improve your wah tones.