Wah Question

[Marcus Dahl]

I'm just now getting into wahs, and am working on building a Vox wah. Instead of 510ohm res. I've a 470ohm, and instead of the the 1.5k res I've put in a 2k. Anyways here is my problem. I get a strange bump sound in the mid-range. So I slowed down the wah action until I found the spot. I found that I get a strange al,ost radio like sound out of it there. Kinda like on the old radios inbetween station sound. I thought maybe it was the pot, but the problem still exists. I am useing a RS transformer at the moment, but it wahs fine and sounds great. What do you think the problem is? Could it be the inductor? I'm stumped  :?

[brett]

Just to be sure that it's not associated with the changed bias on Q1 (due to the 2k replacing the 1.5k),  run a 4.7k resistor in parallel with your 2k.  That'll take the combined resistance down to 1.4k, which should be close enough for rock'n'roll.

Otherwise, this is a bit of an odd problem - the pot should be uncoupled with respect to DC, and simply lets AC through to Q2.  So "crackles" and "bumps" are minimized.  Maybe check that no DC voltage appears at the pot input and output.

sorry I can't offer any more substantial leads...

[Marcus Dahl]

Just to be sure that it's not associated with the changed bias on Q1 (due to the 2k replacing the 1.5k),  run a 4.7k resistor in parallel with your 2k.  That'll take the combined resistance down to 1.4k, which should be close enough for rock'n'roll.

Otherwise, this is a bit of an odd problem - the pot should be uncoupled with respect to DC, and simply lets AC through to Q2.  So "crackles" and "bumps" are minimized.  Maybe check that no DC voltage appears at the pot input and output.

sorry I can't offer any more substantial leads...

I'll change the 2k and see if the prob still exists. I'll also check for the DC, but I would think if tht was the prob it would be across the hole range of the pot. I'll get to it in the morrow. Thanks Brett.

[Marcus Dahl]

Changing the 2k res back to a 1.5k res didn't work, and changing it to a 1k made it wah less, but it did fix it. So this is what I did instead. I put the 2k res back, and put a .001mf cap on the effect output to ground. Problem fixed.