Germanium Diode Filters? (was: EMS Schematics)

[Sean Costello]

At 09:03 AM 11/4/96 -0800, you wrote:
>   From: Christopher_List at Sonymusic.Com
>   Date: Mon, 4 Nov 1996 11:37:05 -0400
>
>   People use germanium diodes in fuzz-boxes to get more tube-like
>   distortion - yes?  My understanding is that this is because they don't
>   have as sharp of a cutoff between on and off as silicon diodes. 
>
>No, people do not use germanium diodes in fuzz boxes to get more
>tube-like sounds.  The Fuzz Face is the famous fuzz box that used
>germaniums (initially) and it sounds nothing remotely like a tube amp.
>That was the point, actually.  I mean, distorto tube amps were readily
>available, tuned buzz-saws were not.  It's still used today because it
>sounds pretty cool, but nothing like a tube amp.

I have gotten some pretty tubey sounds out of a Fuzz Face.  Rolling back the
volume on a Strat just slightly gets you a distortion that is very tube like
in character (touch sensitive, fine gradiations between distortion and
clean, etc.).  By modifying the Fuzz Face circuit (changing the value of the
bias resistor, adding an imput resistor to change the input impedance,
changing the value of the input capacitor), you can get a range of sounds,
from spitting gonzo clipping to full-on Tube Screamer impersonations.  Try
adding a 50k pot at the input of the circuit, set up as a variable resistor,
and adding a 1k pot as a variable resistor in parallel with the 470 ohm bias
resistor.  Changing the input cap to a lower value (say, .022uf) also brings
out those higher frequencies that are considered "tube-like."  Using a
buffer before the circuit transforms the sound from the muddy woofy sound to
a more tube-like sound; perhaps a FET could be used as an input buffer in
the circuit.

>I've run a guitar signal into a pair of back-to-back germaniums under
>various conditions and I was completely surprised at how awful it
>sounded.  Really.  Sort of sitar-like, a buzzy sproing.  Silicon
>diodes and LEDs sounded much more like a tube amp.

I've had the opposite experience.  I've built circuits that use silicon
diodes, and substituted germanium diodes.  The result was a much smoother
distortion, with none of the graniness and farting noises that the silicon
diodes provide.  Of course, this must depend on the circuit, as many
smooth-sounding distortion boxes (Big Muff, Tube Screamer, Pro Co Rat) used
silicon diodes.

Sean Costello