Fulltone 70 fuzz Ge diode?

[patricks]

Hi all!
I'm lining up some fuzz builds, one of which will be the fulltone 70 fuzz. I've got a couple of questions about the 1N34A Ge diode (D2 in this schematic: https://generalguitargadgets.com/pdf/ggg_ff5_sc_b70.pdf)

The first is what's it's function? Referenced to ground just before the output does it provide some assymetrical clipping?
The second is, is it necessary? Genuine 1N34A are hard to find, and pricey when they're available so if it's not necessary I'll leave it out, or if any old diode (or one then similar Vf) will do then that's easy. If it's needed as a "mojo" part then I can find plenty of threads on what to use as substitutes or where to find real ones 

Cheers, Pat

[MaxPower]

Asymmetrical clipping is my guess. Might try a schottky diode if you have one.

[patricks]

Sweet, thanks. That was my guess as well, I'll track down a Schottky:)

[amptramp]

Schottky diodes have a more abrupt knee in the V-I curve than germanium, so if maximum similarity to germanium is required, the Schottky diode should have a resistor in series with it.

[patricks]

That's great to know, thank you 
Is there a good range of values to start within, or best to just test and listen?

[MaxPower]

Iirc about 100 ohms is a good start. There's a web page or blog where someone experimented with this idea. Someone else pointed out that this was frequency dependent (ideally, you'd need different resistance values for different signal frequencies).  I experimented with a small pot (500 ohms) but I didn't hear much difference.

I recommended a Schottky  because I think they sound better than silicon diodes. Germanium would be preferable IMO but it's a matter of taste so try them all. Even a MOSFET can be used like a clipping diode.

You might give Craig Anderton's Tube Sound Fuzz a try. Uses a CMOS chip but only a few external components. I really like it as a clean/light overdrive preamp sort of thing. I'm going to build a second one since I omitted the high gain option because I didn't have a switch, though I guess I could have used a second gain pot.

[patricks]

Excellent, thanks, that's easily done 
I haven't been able to find Ge here in Aus for a reasonable price, I have one old Ge transistor missing a leg that was used in a record player but the Vf measured at 0.16V. I'll give it a try for fun anyway

[andy-h-h]

Excellent, thanks, that's easily done 
I haven't been able to find Ge here in Aus for a reasonable price, I have one old Ge transistor missing a leg that was used in a record player but the Vf measured at 0.16V. I'll give it a try for fun anyway

Where are you in Australia?  I have a bag full of GE diodes that will do the job.  DM and I'll pop a few in the post for you.

[patricks]

Oh wow! Thank you!
I'm in Melbourne, DM on its way