The "C3" cap in a Fuzz Face...what value does what?

[mordechai]

I noticed that on GGG's schematic for their Late 60's Fuzz Face circuit, they call for a .1uf cap between the bias resistor and the volume pot.  But on virtually every other schem for this FF circuit, the cap in that positions is .01uf.  I've just built a standard circuit with the .01 and it sounds great, but I've also built a (modified) GGG FF circuit with a .1uf and it sounds rather similar.  What is the primary difference between these two, why does GGG depart from the "norm" in calling for a .1uf cap, and what other alternatives have any of you tried in place of these?

[Quackzed]

the .1uf 'c3' is the output cap. it determines how much bass is allowed to pass to the output, as well as blocking dc. the output cap and the volume pot together make a 'high pass filter'...
http://www.muzique.com/schem/filter.htm
if you plug in the values of the volume pot and output cap in the calculator above, you'll see that a .1uf cap rolls off lows below 3.2hz
and a .01 rolls off lows below 31.8hz... so a smaller output cap will roll off 'remove' more lows...
it works the same for the input cap... a 2.2uf on the input lets practically all the lows in, where a .1 or even a .01 here will cut some bass going into the fuzz and make it sound tighter and less full or bassy...
check out http://www.geofex.com/article_folders/fuzzface/fffram.htm
for a detailed description of whats happening in a fuzz circuit...

[jpiddy118]

If you dig around, you'll hear of people opening up original units only to see everything from .01 up to .1 in there... personally, i found .1 too bassy, .01 too thin, and .047 just right with my guitar & amp. Also, the GGG "Late 60's" schematic is supposed to be a clone of the Fulltone '69 pedal, not an original FF.  never opened one up but maybe that's what Fuller uses.

[mordechai]

Well, the build I just finished has higher-gain transistors, so using the .01uf seems to tame the sound and tighten things up without making it thin.  I like it, but in the lower-gain version I made, the 1.uf did the job very nicely.

[Electric Warrior]

If you dig around, you'll hear of people opening up original units only to see everything from .01 up to .1 in there...

Actually that cap is remarkably consistent in original units. I've got gut shots of over 180 units and I only found one unit with a 0.047µF cap instead of the usual 0.01µF (possibly a small batch around 1971/72, but on only one of them the value is readable in the pic).
I found several undocumented circuit variations, but I'm still looking for one with a 0.1µF cap (or AC128 or SFT363E transistors  )

[jpiddy118]

Actually that cap is remarkably consistent in original units. I've got gut shots of over 180 units and I only found one unit with a 0.047µF cap instead of the usual 0.01µF

I def trust that evidence! could've sworn i read about .022uf as well

[Electric Warrior]

It ain't no evidence. Pretty hard to prove that something doesn't exist. But I guess 0.1µF is more likely a typo than an alternative value based on a very rare circuit variant.

Now you got me watching out for Fuzz Faces with .022µF caps