Rams Head Muff - Polarity

[jammybstard]

I've orderd the parts to build my first BMPi; of all the variations I went for the PNP Rams Head; but looking at the Schem:



As its a Posative Gnd supply I won't be able to connect it to my common 9v supply or else it will short through the interconnect!
Have I read this right? that seems like a huge limitation! or is there a way round it?

[AS74]

Just build it NPN negative ground and have no issue with power supply..
Unless you're goin Ge.  Then use a voltage converter.. worked great with my Ge. Fuzz Face.

[jammybstard]

Ge?? (newish around here)


I have the PNPs and wanted somthing to build these eve; I was thinking use an ICL7660SCPA to make a convertor; I have a couple on the way for somthing else anyway.

[EATyourGuitar]

people generally refer to pnp as germanium or Ge. silicon is Si. when I want to build a PNP fuzz I just make it battery only and I use the stereo jack on the input for a power switch. there have been long threads on the topic of just flipping the polarity where the adapter comes into the box. sometimes it works, sometimes there is oscillation between two power supplies/pedals. I think it depends on the circuits and the power supplies and sometimes luck. but if you want it to be problem free than you can use the voltage converter like AS74 said.

tonepad has one based on the max1044 IC. max1044 voltage converter

[AS74]

ICL7660 is what i used, no problems.  FF is on my board with 9  'negative ground'  pedals and works great.  It's my fave.

[R.G.]

For that circuit, there is no magic in using PNPs. NPN will be fine. Change to NPN transistors and invert the polarity of all the electro caps as well as the power supply.

[jammybstard]

I didn't realise there was such a thing as positive ground pedals; seen as there is and I'm starting to put the bits together for a pedal board, I  might as well deal with it now and build a PSU with pos and neg supplies.

I built the Pi last night PNP, debugged it this morning and it's lovely; smooth and crunchy at the same time; I can see why they're a bit of a must have!





Cheers all

[Electric Warrior]

people generally refer to pnp as germanium or Ge. silicon is Si.

no. both, silicon and germanium can be PNP or NPN.

Ram's Head Muffs usually came with NPNs. The PNP variants are quite rare. 

[EATyourGuitar]

Ofcourse you can have pnp ge or si and npn ge or si. But when your reading pedal forums, bom, schematics etc. Some people use the terms pnp to describe that they are building a pos ground ge ff for example. If they say pnp ff, the rest goes without saying. People arent always clear with descriptions or schematics. You have to play detective some times.

[jammybstard]

ICL7660 is what i used, no problems.  FF is on my board with 9  'negative ground'  pedals and works great.  It's my fave.

Is that on the same power-supply as the rest of your pedals?
If it is I dont see how it work.
The Ground of your Neg-Ground pedals and the Ground of the Pos-Ground pedals will still be at different potentials and would still short out when you connect them together!

[EATyourGuitar]

they dont short. one is +9v with 0v ground and the other is -9v with 0v ground. they might oscillate without the voltage converter but that doesnt mean your power supply is shorted. I wish I could dig up that old thread, its on here somewhere.

[jammybstard]

they dont short. one is +9v with 0v ground and the other is -9v with 0v ground. they might oscillate without the voltage converter but that doesnt mean your power supply is shorted. I wish I could dig up that old thread, its on here somewhere.

That's not Neg ground though is it? would that not be Neg supply?