High pitch squeeling in Fuzz circuit.

[BDuguay]

I recently built a Fuzzwah for a friend and it's squeeling. I took a garden variety dunlop wah and added a BYOC Fuzz Face board and it's all good except for the oscillation when the volume and fuzz pots are maxed. Any ideas where to start looking?
Thanks,
B.

[jlullo]

did you wire it negative ground, using PNP transistors?

[BDuguay]

Yup.

[R.G.]

And another one bites the dust.

See all of my posts on PNP germanium circuits rewired to negative ground.

[rocket]

And another one bites the dust.

See all of my posts on PNP germanium circuits rewired to negative ground.

I have the same problem with a Silicon NPN Fuzzface (BC546a) - I think it's due to my habit of using 90% of the holes in the perfboard. :-)

[BDuguay]

Oh wait, I may have misinterpreted the question. This Fuzz circuit uses BC108's
B.

[R.G.]

If you used BC108's in a negative ground circuit, and you have properly reversed all the other polarized stuff for negative ground, then you have sidestepped the "reversed-ground" mystery.

That puts you back to normal problems with squealing. 

The BC108s are high gain silicon devices with responses almost to infrared light frequencies. Grounding is critical, wire routing is critical, low power supply impedance is critical. You need to use good grounding practices as well as making sure that you don't feed signal from one place to the other by wire capacitance. Not knowing more about the layouts, I can't do much more from this distance.

[BDuguay]

I kinda figured that's where the problem would be. I have a picture showing how it's all put together. Tonight I'll make my first ever attempt at posting a picture starting with that one. I'm sure once you see how it's layed out you'll be able to pin point some sketchy wire routing.
Thanks everyone.
B.

[BDuguay]

Here it ishttp://www.flickr.com/photos/13193429@N00/1805354399/
Now, how do i attach the actual picture and not the URL? I'm so lame.....
B.

[StevanL]

And another one bites the dust.

Just found this out too  I built a Fuzz Face clone using GGG's Negative Ground layout
- I don't know why I picked this option, but it wasn't made clear that it would be a load of rubbish
at the time. Anyway, it sort of worked ok as long as I didn't put fuzz on 10 (Awful fuzzy oscillation/feedback)  or turn my guitar volume
down to zero (theramin squealling sound that changes in pitch as you minutely tweak the volume up). There was also a very light motorboat
sound when the effect was in bypass mode (fx input grounded)

Anyway, I rewired it to +ve ground and it is like a different pedal 

[R.G.]

Here it ishttp://www.flickr.com/photos/13193429@N00/1805354399/
Now, how do i attach the actual picture and not the URL? I'm so lame.....

To insert a picture, you click on the "image" icon in the message composing page, and it inserts 'img' html.

But the picture tells the story. Long leads running over the input jack. Plenty of ways to capacitively couple high level signals from the fuzz to the buffered input. It's possible that there's something else, but that's where I'd start.

Ideally you would use shielded wire for those leads over the input jack, or somehow shield the input jack itself. That would be a good first step, I think.

[BDuguay]

Thanks for having a look at it R.G., once I get the pedal back I'll dig in and work at that.
As for the picture posting problem I'm having, I've tried what you suggested but no worky. What exactly am I inserting once I've clicked the image icon? That's the part I'm not clear on.
B.

[BDuguay]

[BDuguay]

Okay, that didn't work

[BDuguay]

Finally!