Awhile back I built the Big Muff Plus by Mic Tester, over at FreeStompBoxes.org. This is a Big Muff with a JFET input and output buffer, and a James tone stack, which offers Bass and Treble controls, for a wider range of adjustment than provided by the traditional Big Muff tone stack. I wrote about it here.
This build worked pretty well, and sounded good. There was an issue with the range of the Bass and Treble pots, useful zone of each pot was bunched up at the ends of the rotation. I figured this was due to the wrong pot taper. I used (LOG) A1M and A500K pots it seemed like this needed (Reverse LOG) C1M, and C500K.
I put this aside for a while, I picked up of reverse log pots and got it out again to tinker with. The pots in the original schematic are shown as 1M LOG, and 470K LOG. I thought this meant A or Audio Taper which didn’t sound right.
I replaced the pots, now the range of adjustment is spread across the rotation. Now I noticed another issue, Maximum Treble is at the counter clockwise rotation, which seems backwards. It’s possible that I swapped the outside pins on the pot.
On closer inspection, I realize this is the case! The little arrow is pointing up for both pots in the original schematic, and on mine the arrow for the treble pot points down!
Seems like the Bass pot should be a Reverse LOG, C1M, and the Treble pot should be LOG, A500K. I soldered a couple wires on the outer legs of the Treble pot, and everything is working as expected.