Ge Big Muff Attempt II: NPN to PNP??

[trad3mark]

Right, so a while ago i made a Germanium Big Muff. It's awesome sounding, but there's a very faint, albeit audible squeeling from it. Not sure what's causing it, but that's not really why i'm here. (although any help with that would be great )
I forgot i had a tonne of these awesome Russian Germanium PNPs. I've only used them once, in a Fuzz Factory, and they sound beautiful. So I was thinking, I bet these would sound great in other Fuzz's. What's my favourite fuzz? Well you don't get any points for guessing correctly. Which leads me onto my main question. What about a PNP Big Muff, that still has the normal negative ground? I've been looking at PNP vs NPN circuits, and it seems like there's two ways of making the jump. The easiest/most common, seems to be to flip all the polarised components, like electrolytes, and flip the battery. Not a problem, and easy to do. I've seen that in the Yrotcaf Zzuf (Limited Edition Fuzz Factories). But I've also seen another method, which i'm not famiar with.
If you look at the PNP/NPN symbol in such a way that the line where base is points vertically, and, for example, the arrow for the emitter is at the bottom (ie, an NPN). Now, lets say we drew a horizontal line through the middle, sort of an axis. The Base is right on the axis, and then the emitter and collector are on opposite sides. Looking at, for example, the big muff schematic, at one of the clipping stages. There's resistors from base to ground, and from the emitter to ground. It seems to me that if you go to change from NPN to PNP, you can sort of "flip" the circuit across this axis, and keep the battery where it is, if that makes sense. I could be wrong about this, and i'm about to go test it on a sim program, but can this be done? Can you fix my earlier squeeling problem?
Cheers,
N

[R.G.]

Here's the problem. While it is theoretically possible to attach signal ground to either the positive or negative side of any circuit, in some situations it simply does not work well.

Your question

What about a PNP Big Muff, that still has the normal negative ground?

is a common one. The problem is that some of these conversions have intractible oscillation that cannot be solved by any means I've found short of reconnecting the ground where it "should" go. Some, even most of them work fine. But a percentage do not, and have no simple cure. These last all suddenly quit oscillating when the grounding is UN reversed.

You can test it in a sim program all you like, and it will work fine. This is because, to the simulator, power and ground are identical except for the DC level. This is a limitation of simulators - you can never simulate all of the tiny side effects. To work with sims well, you simply have to understand that there are things which do not get into the model. It is, after all, a model. It has to be verified in the real world.

I've posted exactly this advice about not counting on positive/negative ground conversions for PNP circuits not working many times. The problem is that it does work - mostly. People who do it and get away with it think I'm full of it - until they build one of the ones which will not work, and are instantly fixed by flipping the ground around.

Your squealing problem is probably not a well-bypassed power supply or a ground wiring issue. There are others, but those are the common ones.

[Hides-His-Eyes]

You could just create a 'real' -9V from a MAX1044 IC and still run the unit on a daisy chain; expensive IC but simple circuit.

[trad3mark]

R.G.:
Sounds like although it is theoretically possible, I more than likely won't get the desired results, and it'll probably be more trouble than it's worth to do. As for the squeeling, I noticed that i missed the solder on the - end of the 100uF cap going from the +9v to Ground. I left my soldering iron at home, but that's probably it, right? Anything else i should check?

Hides-his-eyes:
Yeah a polarity-reversing type circuit is always an option. I'll look into that for sure. I know there's a few chips in my local part suplier that has other regulators that will output -9V. I'll investigate that this weekend.

[Derringer]

But, if you have PNP transistors and are using a battery, you could just build the circuit specifically for a positive ground and "ideally" not get the possible oscillations/side effects of trying to use PNP Q's with a negative ground ... yes?

Would you be using a battery or a power supply ?

[Hides-His-Eyes]

Hides-his-eyes:
Yeah a polarity-reversing type circuit is always an option. I'll look into that for sure. I know there's a few chips in my local part suplier that has other regulators that will output -9V. I'll investigate that this weekend.

Be aware that many are not designed specifically for audio and may have sub-20kHz oscillators inside.

[mac]

When I was experimenting with a Ge PNP Big Muff I followed RG advice: If you use PNP transistors go positive gnd. After all you can build a cheap PS for all your positive gnd pedals.
A positive gnd pedal is not an abomination...

mac

[Derringer]

When I was experimenting with a Ge PNP Big Muff I followed RG advice: If you use PNP transistors go positive gnd. After all you can build a cheap PS for all your positive gnd pedals.
A positive gnd pedal is not an abomination...

mac

what with all the diode clipping that goes on in the BM circuit, did using Ge transistors make much of a difference in sound Mac ?

if yeah ... can you describe it ?

[petemoore]

  I think you nailed it & diodes are setting the cieling and the PNP or NPN transistors seem to be having no troubles exceeding the threshold, as shown anyway.
  Seeing scope charts of the transistor would probably reveal that the above  diodes chosen dwarf the PNP or NPN relationship to the sound, or just remove the diodes, and see if the units sound different, odds are they will given the # of parts, and and tolerances.
  I tried some Ge's but a whole different ball of wax, noiseyness, not enough gain issues with that. Might be worth it with the 'right' transistors and fairly high thresholds in relationship to the gain so the transistor tone contributes noticably.
 
 

[Derringer]

right on

and I'm very sure that I read something here posted by R.G. or maybe Mark, maybe John (sorry, can't attribute the info exactly to its origin) that even the bias of the clipping stages isn't all that relevant due to the clipping thresholds involved

that's just the un-transparentness of the circuit   ... goes in one end ... comes out Big Muff

different diodes/no diodes like you said Pete, will definitely make a difference though

and I suppose I could see how a Ge tranny in the gain recovery stage could change things slightly ... but i don't know

so I'm interested to hear the results

[trad3mark]

I made a totally ge muff a while ago. GT404B transistors, and D17 Diffusion Diodes. VERY different to the standard muff i have. It's much less angry, but it's an absolute joy to use. I'll use it in one of two ways. I'll have tone rolled all the way to the bass side, and sustain on full, for a wierd, mega muffled hipsteresque alternasound. It's really really thick. Like playing a muff through treacle. The other way is to have sustain on full, and tone at about 1-2 o'clock. It's a much more balanced tone sound, but the fuzz sound you get of it can only be described as a normal muff that's not angry.

Thinking of trying out a "hybrid" muff; Si transistors, Ge diodes, or vice versa.

[mac]

what with all the diode clipping that goes on in the BM circuit, did using Ge transistors make much of a difference in sound Mac ?

if yeah ... can you describe it ?

To me it sounds more fuzzy, less bright... much like the difference when you compare a ge FF with a si FF.

mac

[caress]

Hides-his-eyes:
Yeah a polarity-reversing type circuit is always an option. I'll look into that for sure. I know there's a few chips in my local part suplier that has other regulators that will output -9V. I'll investigate that this weekend.

Be aware that many are not designed specifically for audio and may have sub-20kHz oscillators inside.

LT1054 is great