positive ground to negative ground

[sir ladderhole]

hello
i was planning on building the triangle big muff pi ( http://diystompboxes.com/pedals/tribmp.gif ) until i realized it was a positive ground. i already have most of the parts, so i was going to try to build it as a negative ground instead. if i was to do this, all id have to change besides the ground is the polarity of the capacitors and change the transistors from pnp to npn, right? thanks
-chris

[R.G.]

To change the polarity of any circuit:
1. Exchange all transistors for the opposite type: NPN -> PNP and PNP->NPN, n-channel ->p-channel, p-channel -> n-channel.
2. Reverse all two-leaded polarized components: diodes and polarized capacitors.
3. Reverse the power supply.

[Floyd Pepper]

Well spotted.  I daisy chained my Fuzz Face and Tube Screamer off the same power supply forgetting the groundings were different.  I blew the PSU and the 4558 chip in the TS.  It was an original TS-9 too. 

[col]

Look for the npn schematic as there is one for this pedal but I don't have my info with me at the moment. Alternatively look for the 3 knob foxey lady which is the same circuit and uses BC184C npn transistors. I also recently built one with BC549C trannies for a sound engineer after he was extemely impressed during a recording session. Since the diodes are in pairs and there are no polarised caps in this circuit I don't think it really makes any difference other than your power connectors.

Col

[sir ladderhole]

thank you guys. floyd, that is bad news. the first pedal i built was a positive ground and it took me forever to figure out why it wouldnt work with my others.. so i stay away from them now. i have the npn schematic as well but some of the parts are different - mostly resistors and such, but i am broke and cant really afford to buy more parts at the moment. would i be correct to assume that the base, collector, and emitter of the transistors would stay in the same positions?

[Floyd Pepper]

This link shows a positive ground boutique fuzz
http://www.diystompboxes.com/smfforum/index.php?topic=42400.0

and this one a negative ground boutique fuzz
http://aronnelson.com/gallery/album17/BOUTIQUE_1969_FUZZ_FACE?full=1

I built the negative ground version and it's my fave fuzz.

[R.G.]

I tell you three times: You cannot rely on a negative ground version of a PNP distortion pedal to work without oscillation. It is prone to oscillation that can't be fixed by anything but reconverting it to positive ground.

I tell everyone this every time it comes up,  but they still keep trying. Some of the conversions work OK, but some of them don't and they can only be fixed by making them positive ground again. Those layouts and schematics need to be marked with this warning to keep beginners from simply expecting them to work. There is a steady drizzle of people who try the negative ground version of a PNP pedal and can't figure out what's wrong.

Note that this is different from reversing the polarities of all the parts inside the circuit. The bad one is simply reversing what you call "ground" and "power".

[Floyd Pepper]

RG, Thanks for the info.  I checked and I actually built the positive Boutique Fuzz.  I built the positive after reading this thread where the motor boating issue was discussed in relation to the Boutique Fuzz.  http://www.diystompboxes.com/smfforum/index.php?topic=42400.msg306680#msg306680 

I'm glad you chipped in here as I'm half way through making a negative ground SkyRipper.   I was making negative as there's a perf board layout for it (and I'd forgotten your wise words which I've read before).   I'll switch to Positive as Joe Gagan intended it.

If negative has issues why do people create layouts for them?

[petemoore]

  BTW Aron here sells the NPN Ge Transistors...they can be used with 'standard' Neg Gnd Circuits.