Sharing pots (2 in one fuzz face PNP/NPN)

[Kevin Mitchell]

Hello everyone, I'm sure this isn't a new idea but I would really like some help trying to figuring this out and I'm not sure how to go about looking up how to do this. I've looked around a bit but my lack of knowledge/experience limits keywords for my search.

So the topic is pretty straight forward. There's always this fuss about which fuzz face sounds better (too much to consider here) but it's always between the red and blue fuzz face (germanium and silicone). The schematics are VERY similar of course with some discrepancies. The biggest being the polarity (germanium runs on -9V and silicone +9V. This topic isn't about what sounds good and what sounds bad. It's just about getting these these two together.

I've been trying to think of ways of using a switch to activate which circuit I want to use but while using the same controls but also without circuits interfering with each other. They would share the power supply, volume and fuzz control. Easier said than done perhaps?

Either way I want to know! What's the best way to go about this? I'm certain this had been done before. I recall seeing something similar in a gallery floating around somewhere. It was a 3 in one box and the fuzz section had this switching ability I am describing. Or at least that's how I remember seeing/reading about it.

Please be descriptive. Draw out an image if possible (literally if you'd like)
I really appreciate it guys.

Here's a write up by R.G.  Thank you R.G. for bringing out so much detail regarding such a simple circuit. LINK
Schematics;

[digi2t]

Using the same controls, maybe dual gangs? One half for one fuzz, and the other half for the second fuzz. Since they both use the same values...



As for switching between the two, one footswitch for the bypass, and a second for switching fuzz. I think it would have to be wired to ground the input of the unused fuzz, to avoid any possibility of oscillation? I'm guessing here.

[Kevin Mitchell]

Ahh dual gang pots. Didn't consider that! Although I was hoping for a different way.

I'll add that to my list of possible methods. There's allot to think about and consider here. I'll draw something up once it becomes more clear.

[Kevin Mitchell]

Here's a thought that should do it,

Dual Gang pots and this toggle;


Switching power, input and output between two separate circuits should do it. Don't you think?

I'm just assuming here. I just looked up a 9 pin toggle thinking that's how it would work. And if so then the answer is far more obvious to me opposed to an hour ago lol.

[GGBB]

You generally don't want to be switching power on and off in a pedal, but if this is just experimental don't worry about it.  Otherwise, it is possible for a positive ground pedal like a PNP fuzz and a negative ground pedal to share a power supply. Here's a fuzz example from AMZ



With this setup for the PNP fuzz, it can share the same power supply with the NPN fuzz so you don't have to switch power. Then all you need to do is switch the inputs, outputs, and the fuzz control including 20uF cap to ground from wiper. This will allow you to use single gang pots. Input switching is obvious. For output switching, just separate the volume control from the circuit and switch the circuit output connection to volume pin 3. You could also include the output cap as part of the volume control if you wanted. The fuzz pot and cap would be switched between the two circuits at pin 3. This leaves the .001u cap in the JH1 from Q2 emitter to fuzz pot wiper - someone should confirm this, but I think you can get away with connecting this to ground from Q2 as this would effectively do the same thing since the path from Q2 through the .001u cap then goes through the 20u cap to ground, and the series capacitance of those two caps would be extremely close to .001u anyway. I think this should work fine - switching out the fuzz pot might be an issue but I don't think it will. If it is a problem, you could try a 1M or larger resistor to ground on each Q2 emitter (parallel the fuzz pot) that is left in place when the fuzz pot is switched.

[Kevin Mitchell]

That's a good bit of information thank you for the ideas
But I'm trying to avoid altering the circuits to keep it classic if possible.

The more I think about it the more obvious the solution seems. It makes sense to me but I'm afraid the circuits might still interfere with each other because they share the same power although I think this would be no different if I were to daisy chain two different effect boxes. So I would have to switch in, out and their grounds (ground connection of the jacks, not the circuit itself).

So would it be a problem to daisy chain a negative ground circuit and a positive ground circuit in one box while sharing the power supply? I wouldn't think so. But I do fear while one circuit is omitted it's input, output and their grounds it would alter the voltage shared between the two circuits. I'll breadboard something tonight to figure that part out but I'd like to know what you fellas here think.

So dual-gang pots (500k log and 1k lin)
A 3PDT switch for in, out and their grounds (4PDT for light indicator)

And that should do it.

[Luke51411]

That's a good bit of information thank you for the ideas
But I'm trying to avoid altering the circuits to keep it classic if possible.

The more I think about it the more obvious the solution seems. It makes sense to me but I'm afraid the circuits might still interfere with each other because they share the same power although I think this would be no different if I were to daisy chain two different effect boxes. So I would have to switch in, out and their grounds (ground connection of the jacks, not the circuit itself).

So would it be a problem to daisy chain a negative ground circuit and a positive ground circuit in one box while sharing the power supply? I wouldn't think so. But I do fear while one circuit is omitted it's input, output and their grounds it would alter the voltage shared between the two circuits. I'll breadboard something tonight to figure that part out but I'd like to know what you fellas here think.

So dual-gang pots (500k log and 1k lin)
A 3PDT switch for in, out and their grounds (4PDT for light indicator)

And that should do it.

You wouldn't be able to run a negative ground and positive ground circuit off the same power supply. Have you considered adding a charge pump voltage inverter for the positive ground effect? Then you would have no problem running them off of the same power supply.

[Kevin Mitchell]

You wouldn't be able to run a negative ground and positive ground circuit off the same power supply.

Are you sure? That doesn't seem right to me. I see people daisy chaining(shared power supply from single transformer) pedals all the time and I've never heard of an issue regarding a negative ground pedal not working in the chain. Perhaps I should look into that.

As I said, this is the only possible issue I can figure from this;

But I do fear while one circuit is omitted it's input, output and their grounds it would alter the voltage shared between the two circuits.

Have you considered adding a charge pump voltage inverter for the positive ground effect? Then you would have no problem running them off of the same power supply.

That is definitely an alternative I'd go with but no I didn't think of that. I'm still learning.

[slacker]

Are you sure? That doesn't seem right to me.

Afraid so, you can't run positive ground and negative ground pedals off the same power supply. If you have a fancy power supply where all the outputs are isolated from one and other then you can as this is essentially the same as having lots of separate powers supplies in one box.
This is why you can't do it, your power supply has two connections, positive and negative. In a negative ground pedal, the negative of the supply is connected to ground and the positive is the power (+9 Volts). In a positive ground pedal the positive of the supply is connected to ground and the negative is the power (-9 Volts). If you try and make it do both at once then both connections are connected to ground shorting out the power supply.

Hope that made sense

[GGBB]

Are you sure? That doesn't seem right to me.

Afraid so, you can't run positive ground and negative ground pedals off the same power supply. If you have a fancy power supply where all the outputs are isolated from one and other then you can as this is essentially the same as having lots of separate powers supplies in one box.
This is why you can't do it, your power supply has two connections, positive and negative. In a negative ground pedal, the negative of the supply is connected to ground and the positive is the power (+9 Volts). In a positive ground pedal the positive of the supply is connected to ground and the negative is the power (-9 Volts). If you try and make it do both at once then both connections are connected to ground shorting out the power supply.

Hope that made sense

+1

[nocentelli]

Are you sure? That doesn't seem right to me. I see people daisy chaining(shared power supply from single transformer) pedals all the time and I've never heard of an issue regarding a negative ground pedal not working in the chain. Perhaps I should look into that.

Almost all commercial effects pedals use 9 volt negative ground (or "positive power") supplies, so sharing a daisychain isn't usually a problem. A stock pnp fuzzface needs positive ground so cannot directly share a power supply with most other pedals. You can either use a separate battery (as most vintage or vintage-style fuzzfaces, e.g. from D*A*M), a voltage inverter chip converting your daisychain's +9v to -9v (keeping 0v as the reference), a separate -9v power supply (not ideal for a shared enclosure), or rewire the fuzzface "upside down" as suggested above.

[Kevin Mitchell]

You guys really did dumb that down for me lol (little unnecessary but I appreciate it). I was just typing up that I looked into it and everything to ground will short if I were to move forward with that idea.

So the charge pump is my best bet seemingly. Invert the polarity of one circuit's power supply and then I have no worries about polarities between the two verses the supply.

So! Any recommendations on voltage inverters/charge pumps?

I'll draw up a schematic once this is all situated and then I hope you guys can clear any mixups from there. Thanks for the help guys you all rock

[GGBB]

So the charge pump is my best bet seemingly.

Easiest bet is the negative ground PNP fuzz I posted earlier. There is effectively no difference as far as the fuzz is concerned - read the article: http://www.muzique.com/lab/fuzzface.htm.

[digi2t]

DANG!! Didn't even see that one was PNP, and the other NPN. Sorry.

Starting to smell like a Two Face fuzz. 

[Kevin Mitchell]

So the charge pump is my best bet seemingly.

Easiest bet is the negative ground PNP fuzz I posted earlier. There is effectively no difference as far as the fuzz is concerned - read the article: http://www.muzique.com/lab/fuzzface.htm.

Alright thanks I will breadboard the difference between negative and positive ground PNP Fuzz Faces tonight to see if there is any difference to my ears. I wanted to avoid altering the original schematics but since I'm working from scratch here there's no foul in experimenting. As long as I can't tell any differences lol.

[Luke51411]

If you wanted, there are a few pcb sites that sell fuzz face boards with a charge pump on the board, build one of those and you are ready to go. There is a guy on the forum too selling those and standalone charge pump boards, just look a ways down in the buy sell trade section.

[Kevin Mitchell]

Edited because I'm at work and can't focus on what the hell I'm doing

[GGBB]

The only thing that changes is the polarity of the input cap. The volume and jack grounds don't need to change since they are isolated from DC by the input and output caps - they stay connected to ground, but ground is what changes. Here's a redrawing that illustrates it even better:

That seems ridiculously simple and I wouldn't understand why that isn't traditionally done today.

Vintage vibe mojo

[nocentelli]

It is done today, the Lovepedal silicon fuzzmaster uses 2N3906 pnps with a +9v supply, but flips the power upside down. I'm sure some other boutique Ge fuzzfaces also use this. However, I have read RG mention that it can sometimes cause unpredictable oscillation, so a voltage inverter might be a better bet. I've used the ICL7660S  successfully a few times to provide a bipolar supply from a 9v daisy chain, just make sure it has the "S" suffix so the switching frequency can be boosted well above the audio range to avoid charge pump whine.

[Kevin Mitchell]

So yes to the fact that the - ground PNP version just flips the input cap around and grounds volume, in and out to - instead of + apposed to how it's traditionally done.