Positive ground version of two interesting circuits....

[mordechai]

Is it possible to construct the AMZ mini-booster or the ROG Professor Tweed as positive ground circuits??

[cpm]

probably, you'll need to substitute n-fets fot p-fets

[R.G.]

Is it possible to construct the AMZ mini-booster or the ROG Professor Tweed as positive ground circuits??

Possible? Sure.

But WHY??

[mordechai]

R.G. -- no reason.  I am just trying to clarify things, theoretically, as I become more familiar with these circuits and eventually design my own.  I don't have specific plans right now, I was just thinking academically.

[mordechai]

CPM -- when you say that I need to swap n-fets for p-fets...what is the p-fet equivalent of the J201?

[R.G.]

R.G. -- no reason.  I am just trying to clarify things, theoretically, as I become more familiar with these circuits and eventually design my own.  I don't have specific plans right now, I was just thinking academically.

OK. Theory lesson.

There are two ways to swap grounds.

1. Invert the polarities of all polarized components, then invert the power supplies (which includes ground if it's a single polarity power supply). So all polarized caps have their +/- reversed, all diodes are swapped anode for cathode, and all semiconductors are swapped in polarity, as in N-channel for P-channel and vice versa, and NPN/PNP. That's the theory. In practice, you may or may not be able to do this, because some semiconductors have no reverse-polarity device commercially available that I know of, like SCRs, some triacs, UJTs, possibly some others. And of course, if it's a tube circuit, there are no P-type tubes, as positrons are dangerous (and unavailable outside particle accelerators) and protons don't emit from thermionic surfaces like electrons do. On a more limited practical side, the inverse-polarity semiconductors (N-for-P channel and NPN for PNP) may not give the same gain, frequency response, etc. , so the reversed circuit may not work as well, or the same, as the original.

2. Just swap what you call power and what you call ground, and use capacitors to block any DC offset issues. This is the classic "make a negative ground pedal out of a PNP fuzz face" mod that gets bandied around, and told for the gospel. Sometimes it works. Sometimes it does not, for reasons that are not totally clear, but probably have to do with the impedance of what is called ground in which case and how well decoupled the various supplies are to whatever becomes real ground. I've spent a long time on this issue, because I was frustrated that I could not always make it work. I was able to get it to work in many cases, but importantly, not all cases. In all of the hard cases, reverting to the "proper" grounding made it work. This trick works often enough that it refuses to die, because everyone who gets it to work thinks OK, it *always* works because it worked for me. You have been warned... 

In your question particularly, CPM goes to the heart of technique 1 - availability of the reverse-polarity devices. What is the p-fet equivalent of the J201? There may not **be** one. P-channel JFETs are much less common than N-channel for reasons having to do with the solid state physics of silicon.

And if your question is can you do a technique 2 on these circuits, then the answer is sure - but don't kill yourself making it work if it oscillates or has hideous noise. It may not be possible to cure a technique 2 mod for this circuit and the specific devices you use. In general, the more gain and more complex a circuit, the more difficult it is to get it to work with technique 2.

[WGTP]

http://www.diystompboxes.com/analogalchemy/sch/obsidian.html

This is a positive ground version of the Obsidian Overdrive (a great sounding distortion) which uses the P-channel version of the BS170 mosfet, the BS250.  Joe says the P-channel mosfets are quieter.  A single stage can be used as a mosfet boost.  I have used the BS170 and BS250 together in a complimentary stage.  This is the only P version I'm aware of.     

[petemoore]

  Anything E-directional will notice an electron flow reversal, polarized components will be reversed.
   Some parts invert perfectly, I heard but didn't research at all something about doping processes which make for slight differences between the inputs of N and P devices.