Re: Fuzz boxes

On Sun, 23 Feb 2025 23:30:41 +0000, TTman <kraken.sankey@gmail.com>
wrote:

Can anyone explain why the best ones seem to use germanium transtors, (
and 'matched pairs' at that)? Why not a simple op amp with back to back
diodes? Any circuits?

This doesn't answer your question, but might offer a vague example of
the differences in the sound (distortion) produced by Ge vs Si
transistors:

"Arbiter Fuzz Face"
<https://fuzzcentral.ssguitar.com/fuzzface.php>
"They do sound different from the original Germanium versions, usually
with a more harsh and aggressive clipping as opposed to the "soft"
clipping characteristics of Germanium."

My guess(tm) is "harsh and aggressive clipping" translates into more
high order harmonics for Si.  On an oscilloscope, that would look like
a rounding of the sharp corners of any fast risetime waveforms. 

A few decades ago (about 1967?), I would try to repair almost anything
for anyone who walked (or crawled) into the shop.  I don't recall the
maker or model of the fuzz pedal but it looked something like this:
<https://reverb.com/item/84878514-vintage-60s-70s-jen-fuzz-tone-bender-guitar-pedal>
Notice the $2,200 asking price.  The basic problem was that all the
knobs and potentiometers were bashed in by gorilla with a very heavy
foot.  Oddly, the switch survived.  After replacing the knobs and
pots, I found that the Ge input transistor was blown.  I couldn't find
replacement in Ge, so I substituted a Si transistor.  The owner paid
me but soon claiming that it didn't sound right.  I soon found a Ge
transistor.  I couldn't hear the difference but the owner claimed that
the Ge transistor sounded "better", whatever that means.

As for using an op amp and diode clipper, it's possible.  However, my
guess(tm) is that the typical buyer is trying to imitate the sounds
produced by the name brand players.  It's quite easy to produce a
linear and low distortion device using modern components.  Reproducing
the strange noises and non-optimal sounds belched by a device full of
sub-optimal components, is actually quite difficult.  For example, how
does one design something that has the proper "presence" and
"ambience"?

Note that some of the effects projects at:
<https://fuzzcentral.ssguitar.com>
use op amps and back to back diodes (usually Ge).  You might try
building one of those. 

--
Jeff Liebermann                 jeffl@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann      AE6KS    831-336-2558