Help with malfunctioning Wah

Started by Astronaurt, May 17, 2011, 09:04:05 PM

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Astronaurt

I built a Wah Pedal Circuit from the schematic here: http://fuzzcentral.ssguitar.com/mccoy.php

with the output buffer. The only part substitutions I've made are a 100k trimpot for the 100k Resistor paralelling the Inductor, a 1uF cap for the 0.05uF cap at the input of the output buffer, a 6K8 resistor for the 4K7 resistor on the source of the output buffer JFET, and the JFET I'm using is an MPF102 just because it was close at hand. Here are the Voltages on all three Trannys:

Q1
C: 4.1V
B: 0.69V
E: 93.8mV

Q2
C: 8.82V
B: 4.1V
E: 8.81V

Q3
G: 8.02V
S: 8.82V
D: 8.82V

The pedal does not have any effect when engaged. At first I thought there was a problem with the DPDT switch I'm using in there, so I used alligator clips to make sure the necessary connections to get the signal to go through the circuit were made. And yeah I got nothin', the sound coming in sounds the same as the one coming out with maybe a small decrease in treble, and rocking the Wah pot has no effect. At first glance, it seems like something's wrong with Q2's stage, and maybe something's wrong with the output buffer stage, but I'm by no means on expert. So I'm pretty lost on where to start looking for problems. Help would be wonderfully appreciated!

Paul Marossy

The voltages on Q2 & Q3 don't look right to me.

StereoKills

Neither do the voltages on Q1 I think.

I'd start by looking for a short somewhere between the grids connected to the emitter and collector of Q2. These should not be the exact same voltage by any means, and probably point to the cause of at least one of the problems.

Is there any way that you can post pictures of the board? That could help out significantly.
"Sometimes it takes a thousand notes to make one sound"