Positive Ground Oscillation with power supply

[Chris oej]

Hi

I've built a Tone bender MKII using OC81Ds (PNP) transistors - with a battery plugged in it sounds perfect. However, when i plug in a 9v power supply i get a high pithed whine - it sounds like something is self oscillating. I assume that this has something to do with the fact that it's positive ground. Below is the wiring setup i've used. I can't work out why this is happening. I've searched through this forum but can't find anything.

Does anyone know why this might be happening?

Thanks

http://www.generalguitargadgets.com/diagrams/switch_lo_3pdt_tb_dcj_pnp.gif?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

[R.G.]

1. Which 9V supply?
2. Do any other pedals share the 9V supply?
3. Is there any internal decoupling of the 9V supply?
4. Are  you *sure* it matches the wiring diagram?

[Chris oej]

1. Normal 9v, says on it "replacement for Boss and Ibanez" - Output: 9.6V DC   200ma
2. No
3. No
4. yep, definitely wired right.

Could a just be a case of the power not meaning to be used for positive grounding?

Thanks

[R.G.]

Hmm. Odd.

Question #1 was intended to find out if it was a generic PS not intended for pedals.
Question #2 was intended to find out if it was a cross-loading effect with other pedals, and if it was truly floating.
Question #3 was to find out if it had issues with the internal filter caps.
Question #4 was to find out if it could be a simple wiring error.

None of the answer provides a clear resolution. I would try a different 9V power supply and see if that changed anything. If yes, it's a problem with this power supply and/or the interaction of this power supply with the specific circuit. If no, it's a problem with the pedal circuit inside. In that case, I'd try an internal damping resistor and filter cap of maybe 10-47 ohms and 100uF-470uF.

... and then I'd find my wiring error. But that's how it would happen with me. 

[amptramp]

A number of circuits such as the Fuzz Face have no internal decoupling because the battery is assumed to have a sufficiently low impedance and it was originally designed for battery use with wall wart power added later as an afterthought.  If your power comes in via a long cord, there is no local decoupling and oscillation can happen regardless of the decoupling within the wall wart.

[LucifersTrip]

I've built a hundred fuzzes and the only one so far that does not work well with a Wall Wart (it drops a bit in volume, hisses heavily and the fuzz is not as rich) is a Marshall Supa Fuzz (a Tone bender MKII variant). It also oscillates at full fuzz if the battery is > 9.2v

A filter cap alone didn't help and I haven't got around to that in conjunction with an internal damping resistor

please let us know if you have any luck