Idiot can't build Idiot Wah =)

[Jamforthelamb]

Hey All,

Just recently built the idiot wah using this layout.

And here's the schematic

Got it all done, and the only part substitution was 470kohms for 500kohms.
From what I can tell on the original layout the Transistor is turned around the wrong way, but I put in a socket so I could try it both ways.
Put it one way I get oscillation, turned around the other way the signal passes through, and there is a tiny change when I turn the knob, but not much "wah'ing".

Help?

Thanks!
-jftl

[joegagan]

when the signal is passing, is it lower volume than bypassed?

double check  that your  cuts on the vero  are correct, go through the whole circuit with a continuity check to make sure you don't have a dead short somewhere. go through with the schematic and a pencil and mark off every connection that tests good.

tripe quadruple check everything. everyone here will admit that they  found the problem to be something simple  when the  checked the circ for a fifth time.

[deadastronaut]

everyone here will admit that they  found the problem to be something simple  when the  checked the circ for a fifth time.

oh yes...many times...

[Earthscum]

tripe quadruple check everything. everyone here will admit that they  found the problem to be something simple  when the  checked the circ for a fifth time.

Seriously, +1... that should be the opening line of the debugging thread.

Also, you're correct... the transistor in the vero layout needs flipped around. Other than that, follow Joe's advice, rinse, and repeat... and keep us updated on your success... you'll eventually get it working!

[Jamforthelamb]

OK, I've sextuplet checked everything, and still pretty much the same results. I've added 33k resistors in serial to the 470k resistor bringing them up to 503k, still no drastic change. I've taken out the 10k resistor to 9v and replaced it with wires to a pot so I could adjust that, which all it really does is cleanup the signal. I think the effect is trying to work, it's just very subtle. The resonance switch doesn't change anything at all, and the wah pot does very little, and it's at the very end of it's travel (using a 100k at the moment for testing. I plan on using this circuit in a sequenced wah setup, so I would like the wah to be more pronounced.

Thanks!
Kevin

[Earthscum]

...and you're using the MPSA13, correct? Try taking the filter section out and see what the tone sounds like. It almost sounds like the signal isn't feeding back to the base properly. I may be fooling myself, but I'm suspecting caps or your pot to ground is bad.

[deadastronaut]

wheres the 220pf?...

C3 is 220pf not 22nf...

[Jamforthelamb]

Earthscum: Yeppers, tried a handful of them. I will try your suggestion tonight and see how it goes.

deadastronaut: Saw that, and it's the correct 220pf on my build.

Thanks!
-Kevin

[Jamforthelamb]

Fixed! Found the problem.

There was a trace cut missing just before the output on the board. It's wahing away now  .

I put the corrections on the layout, and added it to the original post. I'll post it here too so if it anyone runs into the same problem.



Thanks again everyone!

-Kevin

[joegagan]

good one!

[joegagan]

a blast from the past: my take on tim's brilliant design: