If you have a new russian big muff reissue (the black one) and know basics of soldering and ability to trace the wiring i recommend making it true by-pass because its not too difficult to do and its worth it... did it to one of mine (as i have another that i'm leaving as stock) also changed the LED from red to yellow and while i was at it i replaced that cheapo stock 9 volt battery clip that tends to fall apart. at some point replacing those awful plastic input and output jacks will be next because those are horribley cheap and are prone to cracking and breaking if the nut is overtightened. (i had to replace the input jack with a switchcraft to my other big muff because of this, though wiring it to the board was a little tricky.)
my two favorite sites for reference:
http://www.generalguitargadgets.com/
http://www.diystompboxes.com/