I put this together a few months back, but only finalized it the other day, and made a Q&D video today. This is an adaptation of the EHX Double Muff, which is a pair of Muff Fuzzes in a box. Somewhere around 1972 or 73, I played at a gig where I had two Muff Fuzzes plugged into my guitar in series. At that time, the unit had a hardwired 1/4" plug sticking out of it, like the old Dan Armstrong modules. Two of them in series looked like a baby's leg sticking out, but it sounded great to me. The Double Muff captures that tone in a more usable form.
The transistor Muff Fuzz is basically a silicon Fuzz Face, set for medium fixed gain. In the Double Muff, the output of the first one acts as a sort of intensity control for the second, though the gain on each is still fixed.
Here's the PGS demo:
Mine adds some interesting bells and whistles, including footswitch engagement of the second stage. Some very interesting tones available.