I think that's correct according to the PCB.
BUT....after reading this thread I went back and futzed with my PA and tried using the Gain/Vol knobs in reverse and it seems to work better.
Crank the left knob then use the right knob as Master and you can get a much more overdriven sound that doesn't happen the "right" way.
So I guess the Gain and Vol knobs are pretty interactive and can be used both ways.