Note that this circuit is slightly different from the version posted here in October. My version is the "reissue" from ~2000, whereas the version IvIark posted is a more modern revision.
I hope it's ok that I modified IvIark's existing layout rather than making my own from scratch. I figured it would be nice, too, in case anyone wants to compare it to the black Russian. But let me know if you'd rather me take it down.
EDIT (2014 Dec 9): Verified! I know it's like eight months later, but I finally built this on Thanksgiving day using this layout, and it works.
Maybe it should include that mids switch? Like in the other Muff layouts IvIark did. I find it an incredibly useful feature that I include in all my Muff builds.
I built me a NYC reissue Muff using the Musikding kit and I found it to be a good one. With the mids switch of course. I know the NYC version doesn't get a lot of love, because everything used to be bettah in the past, but I put it up against a number of Triangle and Ramshead specs builds and it held up quite well.
This is way late for a response, but I just recently built this pedal, finally.
I know a lot of people like the mids switch, but I'm personally not a big fan. I included a mids switch on a black Russian Big Muff build I did a while back, but I've always found myself leaving it in the "off" position. Plus, I built my Russian Big Muff in a 1590BB, and I wanted to fit this one into a 1590B, so I left out the switch for sake of space.
I agree that adding the mid switch is dead easy. I even add it to real PCB muffs (just solder a wire to the collector of Q3). And while I prefer the pure Muff sound as well, its really helpfull in a band situation where you disappear into the mix. Just flicking that switch from scoop to flat can be enough to suddenly cut through the mix again. Which is why I think it's mandatory for those who play Muffs in actual bands. Leave it off at your own peril.