problem with wah heel down position

[tss]

I have built a wah, v846 style with stock components other than two trimmers as the collector resistors of Q1 and Q2 to adjust voltages. Right now they read 3.18 / 3.59 / 8.52 for Q1 and 0.096 / 0.65 / 4.23 for Q2 (E-B-C). I think the voltages are about right. The problem is that when I have the wah is heel down position ("bass") I get some nasty and unmusical distortion when there's high input to the wah. This happens when I use a humbucker for example. Can any suggest a possible cause?

[GibsonGM]

There are probably many fixes/reasons, but for starters, how about a higher value input resistor?  Just a quick thought.
Does it do this into a 'clean' amp, or just when you are really dirty?

Another possibility is finding that 'gain' resistor on the transistor, and decreasing your gain to unity/just above unity. 

Check your lead dress, too, of course.  *shrug*

[Paul Marossy]

The problem is that when I have the wah is heel down position ("bass") I get some nasty and unmusical distortion when there's high input to the wah. This happens when I use a humbucker for example. Can any suggest a possible cause?

What transistors did you use? Sounds to me like they have too much gain and consequently you have distortion.

[joegagan]

get the trimmer on Q2 as close to stock as you can.
adjust the trimmer on Q1 till the distortion goes away.

if the tone of the wah suffers at this point, try raising your input R from 68k to 75k, or lower it to 33k and install a 250k input volume ahead of it.

the above three methods give different results, tone-wise. try them both to see which you like.

lowering the .01 sweep cap to .007 or thereabouts can be a nice solution for HB guitars as well.

[Paul Marossy]

get the trimmer on Q2 as close to stock as you can.
adjust the trimmer on Q1 till the distortion goes away.

if the tone of the wah suffers at this point, try raising your input R from 68k to 75k, or lower it to 33k and install a 250k input volume ahead of it.

the above three methods give different results, tone-wise. try them both to see which you like.

lowering the .01 sweep cap to .007 or thereabouts can be a nice solution for HB guitars as well.

That'll work if the transistor Hfe isn't too high. Otherwise it's an uphill battle to get a good sound, IMO.

[tss]

Thanks! I'll try what was suggested and report back. I am using BC109C (modern production). I actually didn't test them for gain but I guess 400+ for sure. How come this is not an issue with modern wah pedals which have transistors with higher gains?

[Paul Marossy]

Thanks! I'll try what was suggested and report back. I am using BC109C (modern production). I actually didn't test them for gain but I guess 400+ for sure. How come this is not an issue with modern wah pedals which have transistors with higher gains?

That's at the upper end of what usually works well, but if you follow Joe's advice I think you'll be OK. If you were using something like 2N5089s I think you would be hard pressed to get rid of the distortion without tweaking stuff a lot. Personally I've found that Hfes around 250-300 seem to the best all around in a wah pedal (where you can't really hear any noticeable distortion, especially with clean tones).

[tss]

OK so I've sent Q2's emitter to 10K and tweaked Q1's emitter resistor until I thought the situation is better, however this made the heel down position sound like s**t. It has no gain and no "oomph" like it used to have and after a little while I strum the low E string hard (perhaps out of frustration  ) and I could hear the same ugly distortion coming from the amp. Off course I've checked the amp without the pedal and it works flawlessly so I guess this tweaking helped a bit but that's not it. I want to have the gainy bass while having no distortion. I've played a few old wah pedals that had this going on...

[Paul Marossy]

OK so I've sent Q2's emitter to 10K and tweaked Q1's emitter resistor until I thought the situation is better, however this made the heel down position sound like s**t. It has no gain and no "oomph" like it used to have and after a little while I strum the low E string hard (perhaps out of frustration  ) and I could hear the same ugly distortion coming from the amp. Off course I've checked the amp without the pedal and it works flawlessly so I guess this tweaking helped a bit but that's not it. I want to have the gainy bass while having no distortion. I've played a few old wah pedals that had this going on...

Do you have another amp to try it on? Maybe your amp doesn't like your wah.

[tss]

I only have a single amp at home... I have an old JTM45 at my mom's - should visit her soon anyway 
Can you explain on what you mean when you say he doesn't like the wah?

[Paul Marossy]

I only have a single amp at home... I have an old JTM45 at my mom's - should visit her soon anyway 
Can you explain on what you mean when you say he doesn't like the wah?

Maybe the amp you're using is the problem when you give it the wah pedal, causes the amp to distort. One way to rule out that possibility is to try it with a different amp. If it still does the same thing, then must be something with your circuit.

[Helljoen01]

I am sorry to bring this topic back to life, but I am having the same issue and even after switching most of the components, trying different transistors and resistors, I havent been able too get rid of this ugly distortion/feedback in heel down position.. I am wondering if someone knows how to solve this problem, because it completely stopped my Clyde project