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Hey guys, working on a fuzz face type clone but I want to make it switchable between germanium and silicone transistors. It happens that all I currently have are npn si and pnp germanium and I'm wondering if there's a away to wire those up that would allow each to function properly within the same (preferably npn) circuit. Any input would be awesome. I'm kinda new, hope I'm not just restarting an old thread here, didn't seem to come up in a search.

Thanks,
E

So, I guess the first question is what you're trying to accomplish by this. It's not as easy as just switching transistors. Even if they're both PNP or both NPN, you'll have to significantly re-bias after switching from Ge to Si and vice versa.

Just my thoughts, If you're going for two different timbres of fuzz in the same enclosure, you may be best served by building two separate FF circuits in the same enclosure - one Ge and one Si - then just engage the one you want. It's a low enough parts count circuit that it shouldn't be a big deal squeezing two in a 125B.

Thanks for the response Michael. I completely agree, still I guess I'm mostly just interested in the possibility of it or a greater explanation as to why it would/wouldn't work as my understanding of the differences is limited. I saw a beavis page a while back that mentioned a ge/si switch as a basic mod I believe, though I do think it was intended for transistors of common polarity. I like the simple switch idea more for experimentations sake and figured u could easily bias via an external trim pot. I'm curious about how the two would function within the same circuit and especially curious if it's even possible between npn/pnp transistors. Is there any simple solution to getting one in the others circuit? As I said, really just trying to wrap my head around the differences a little better.

Thanks,
E

Also, I'm aware that I could just wire some shit up and watch for explosions, just trying to gain the knowledge with a few less casualties if possible..

Okay, so if you're just just doing this for the sake of experimenting/learning, then the last thing I want to do is discourage you. Yes, it *can* be done. You'll need a couple 3PDT toggle switches for the tranny switching and you'll probably want to do some reading on the Beavis site as well as study a few schematics and understand the biasing a little. As long as you have enough range in your bias pot (it can be external) it can be done. You could conceivably even mount a little panel voltmeter on the outside for measuring bias voltage w/o opening the case - or you could just bias by ear.

I would, however, stick to like polarities (both NPN or both PNP) - trying to switch from negative ground (NPN trannies) to positive ground (PNP trannies) will get ugly

I'm going to +1 the "build two fuzzes." The second fuzz face will need a polarity converter -- you can't use a NPN and PNP fuzz face running off the same power supply without one. Or just buy a set of NPN transistors (Smallbear sells tested sets with the necessary bias resistors).

For one thing, germanium doesn't "sound" like anything. It has leakage and the transistors tend to be lower gain than silicon transistors, but you can get low-gain silicon transistors that will be in the right gain buckets if you look for them.

For another thing, you'd need a four-pole toggle switch to swap out both transistors (there are three pins on a transistor; one pin on each can be left connected because it won't do anything without the others), and that costs almost as much as another set of passive components for a fuzz face. Plus you have to fix it so that both sets of transistors bias to something that sounds good, otherwise you're not making a Si-Ge switch, you're making a Sh-It switch. I'm not saying it's worthless to do it, but there are a hundred things you can do that I think would get you more millage, everything from an external bias control to a negative feedback control to a simple tone control.

FWIW, you can fake leakage with a large (start with 10M) resistors from the collector to base in Q1 of a Fuzz Face when using silicon transistors, and this will usually get Q1 to bias down to more like .5V like a germanium transistor. Silicon fuzz faces tend to bias at 1V or slightly higher on Q1, which is one reason they sound different -- they're both higher gain and they don't squash the input signal as much. Q2 doesn't really matter nearly as much, both because you can bias it and because its function is purely to squash the output of Q1 into a symmetrical square wave by biasing to 4.5V. Most people tend to like Q2 at 6V in a silicon FF, though, which brings us back to needing to make both sets of transistors bias correctly, so you still need to do more than just a switch that would put a fake leakage resistor in.

EDIT: I would be remiss if I didn't mention that it IS possible to use PNP transistors in a fuzz face, but not in the same circuit. You need to flip everything upside down. Take a look at the Keely Fuzzhead for an example.

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Thanks, Jon. As always, you explained that much better than I

I think what we're trying to say is just because something *can* be done, it doesn't necessarily mean it should. If you're just geeking around on a breadboard and can learn something from this, that's awesome - but I don't expect you're going to have a very practical end result.

Hey, thanks for the great responses guys, I've got a lot to learn about transistor functionality and biasing, hi vs low gain, what to expect in various situations, etc. But this info is getting my feet wet atleast so thank you for that. I just checked out the Kelley and I might actually just build that up first and get a feel for the ge/si switch there before I start really digging for other sounds and schmatic structures.

(Y)

-E

You may find what I posted HERE to be of interest--it's the third build down in the post.

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My mileage on this is that you only really need to switch around the second transistor to get enough difference in the tone. I use a low gain silicon in Q1 and switch between silicon and germanium on Q2. I use the Beavis method for switching using a toggle switch, not a foot switch. You'll also need to mount a bias pot on the outside.

I'd recommend that you get an NPN germanium transistor (or two) from a reputable dealer, say Smallbear if you are Stateside, Banzai, or Das Musikding in Europe, or Doctor Tweek UK and make the circuit NPN, not PNP for ease of wiring and the ability to use a regular negative ground power supply without problems. Id also recommend that you buy a PCB for the Fuzz Face and install sockets for the transistors and wire up a pot for the Q2 resistor to use as a bias adjustment as the easiest route for construction.

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