From effdub: I really like the Fuzz Factory pedal, but I never use the Gate or Stability knobs, so I thought it would be cool to slap together a circuit somewhere in the F.Factory neighborhood but with all the wacky noise-maker type sounds cut out. Also, I wanted this circuit to work with common, off-the-shelf transistors, instead of mojo/hype germanium parts.
I started off with something *like* a slimmed-down Fuzz Factory, but what I ended up with was quite a bit different in terms of fuzz structure and overall sound. Just to be totally clear, this circuit is not a clone of the Fuzz Factory.
* You might want to go with higher values for the input and output caps, especially if you normally use single coil pickups. Instead of the stock 10uf, try 22uf, 33uf, or even 47uf for both the in and out caps. You could even go bigger for use with bass. My preference (thanks to my friend Baj2K over at the BYOC forums) is to use a 22uf for the input cap and a 47uf for the output cap.
* There are dozens of transistors you could use in this circuit. Try out different gains in the Q1 (boost) section. Some transistors sound brighter/darker than others, so experiment like mad. Seriously, in the Q2/Q3 spots, I've tried everything from ultra-low gain 2N128's (hFE of about 30) to 2N5087s (hFE of about 400 or so). Having the Bias control top-side makes adjusting for different transistors quite trivial. Experiment!!!
* My personal favorite tranny for Q2/Q3 is the 2N5139. The sound is less "siliconish" than the 2N4402, mainly owning to the difference in gain. These are available from Smallbear Electronics for less than $1 each. The gain on these is between about 80 and 120 hFE, so any transistor in this range should sound about the same.
* Lowering the value of the 10K resistor off of Q2's collector will change the character of the fuzz. Try a 5.1K to start. Lower values will yield progressively sputtery, farty types of fuzz. This is a prime spot for a DPDT switch to swap values.