fuzz theory: achieving sustain without losing treble??

[pinkjimiphoton]

check my thread on the schizoid face. the sweeter "stupid face" may be just what you're looking for

[kat]

Revisiting this because I said originally that I would report on what ended up working... just got side-tracked for a while with other projects.

I did end up trying the double-barreled FF idea that Transmogrifox suggested and it seems to be a winner to the ears of the pedal recipient.  I am sort of surprised because I set it up using "ears" rather than "brains" and I feel like there are quite a few subtleties that I'm not understanding about what it's doing, but maybe I don't care!

Basically what I built was an A side that is a Si FF with caps set to exaggerate treble, and a B side that is a Ge FF set to be more bass-y.  This is switchable so that it can be "A or B" mode (with each circuit isolated from the other so they can't interact), or an "A + B" blend.  For the blend option, I am not buffering either side but just using a 1K trimpot as a divider on the input (this is one of the "didn't think about it just tried it" things).  On the out side, I needed some extra resistance on B to get the levels to balance but then I'm feeding both outputs into a 50K blend pot that routes to a 100KA volume pot.  I hard-wired the 'fuzz' for B but used a 1KC pot for the A circuit. 

The idea, which actually kind-of works, is that in A+B mode, I can roll off the fuzz slightly on the A circuit so that it's more of a bright overdrive.  It then blends with the bass-y, sustainy, germanium-y B side, so you have a range of options for how sharp or muddled you want the sound to be.  And it remains quite responsive to the guitar volume knob, which is always awesome.   

The circuits are definitely interacting in non-trivial ways, which is what I expected but haven't sat down to really understand.  In particular a cap between  collector and base for Q1 on the A side was absolutely necessary whenever the two circuits "see" each other, although I can do just fine without it otherwise. 

I wouldn't have set out to make a switchable Si/Ge FF but I know that's something that people have often built, and I'm surprised at how well it seems to work to try blending them naively.  Somebody with more know-how could probably optimize this and either control or use the circuit interactions intelligently, but it's not bad just on a naive build.

If anyone else tries it, I'd love to hear how it goes, and if you have improvements.  Meanwhile thanks to everyone who recommended other circuit options... more fun things to try and compare in the future...

[thermionix]

Is it all NPN, all PNP, or one of each?

[kat]

All npn.  2N2222s (metal case) for the A side and a matched pair of Ge from Smallbear for the other side. 

[robthequiet]

At the input, do you have one input cap and resistor or do you feed the guitar right into the trimpot? Also, curious about how you set up the A-B switch. Thx! Interesting project.

[thermionix]

All npn.  2N2222s (metal case) for the A side and a matched pair of Ge from Smallbear for the other side.

Sweet.  Would have been a PITA to mix the two types.

[kat]

At the input, do you have one input cap and resistor or do you feed the guitar right into the trimpot? Also, curious about how you set up the A-B switch. Thx! Interesting project.

I am feeding the guitar right into the trimpot. The idea is that I want the input caps to be different for both sides.  I actually would prefer some kind of magic such that I didn't need any resistance in the input of either circuit because I really notice how it affects the sustain for a FF... but it didn't seem sane to just split the signal with bare wire somehow.  In principle the trimpot would help adjust for the differing input impedances of the 2 sides, I think, but I haven't given this a lot of thought and probably should.

The switching is annoying to set up and I am describing from memory as I don't have the circuit here, so hopefully this will make sense.  I have a 4pdt switch, and a 2pdt switch with center off.  The 4pdt switches between "A or B" and "A and B" mode.  In "A and B" mode, the switch connects input to the trimpot, connects output to the blend pot, and the 2 other connections are used to complete a piece of the input leg and a piece of the output leg for one of the circuit sides in this configuration.  When it's flipped the other way, for "A or B" mode, input and output go to the 2nd switch, and the two connections that were routed through the switch are just interrupted so that they are not connected to anything.  That way, in "A or B" mode there isn't any link between the two circuits through the blend pot or trimpot.  Then the 2nd switch just toggles between the inputs and outputs of the two sides independently.