http://www.generalguitargadgets.com/pdf/ggg_tb3bb_sc.pdf (http://www.generalguitargadgets.com/pdf/ggg_tb3bb_sc.pdf)
i'm so used to seeing the 2nd lug of a volume pot be the output that this looks weird to me.
A stage of tone shaping perhaps?
I have never built this circuit but if I recall correctly I remember reading that there were a few different resistor values (47K? and 22K?) used after the 500K or 250K volume pot. I believe that resistor adjusts the output level and the 22K would allow more volume through over the 47K. It might also let more high end through.
The 1M resistor looks like a simple pull down resistor.
i might be wrong, but if i had to guess, the 47k resistor could form a low pass filter as removing it produces more highs and a 'clearer' output. I demostrate this in a video i made recently:
Paul