wah problem

[GabiDamse]

hi, i've breadboarded a vox style 2 transistor wah, I use a small transformer as inductor and the problem is the wah only works when I put a resistor between the base and collector of the second transistor, otherwise the pot isn't doing anything.I also changed the two 0.22 caps with 0.1, what could be the issue? Are the bc108 transistors not good for this? I thought that maybe they have too small gain.
The resistor between the collector and base is a 50k one that needs to be adjusted so that the wah doesn't oscillate in the low end.

[PRR]

Hi. Isn't there usually some resistor there? And what value worked better? I think it would help to link to the actual plan you are looking at.

[Ben Lyman]

Somebody found this in his old Vox wah, it worked for me. Only mistake I can see is the 68r on input should be 68K.

[GabiDamse]

this is the schematic: http://www.geofex.com/article_folders/wahpedl/wah1.gif , it's the same as the one posted by Ben, the two 0.2 caps next to the potentiometer are the ones I changed with 0.1 and I haven't tried a value bigger than 50k but It works even with the pot turned almost to zero and when at 50k it starts to oscillate in the low end

[PRR]

The 470K from Q1 C to Q2 B "should" bias-up nearly any BJT transistor at Q2. A 1Meg from +9V (Q2 C) to Q2 B might do a similar thing, more variable with different Q2 parts, so I think the stock plan should be fine. (As confirmed by many thousands sold.)

If you "need" a resistor +9V/Q2C to Q2 B, I'd look for a bad joint on the 470K part. After that we may need voltage readings.