Leave the Master at 10, and use Volume 2 to contol output level. Mine would always sound "odd" if I tried to lower the Master.
Input 1/Volume 1 feed into Input 2/Volume 2 for cascading gain. As such, Input 1 was designed for guitar and preamp distortion.
It uses a Fender tone stack, which is flattest at settings of 0,10,0 for treble,mid,bass. My recommendation is to start flat and adjust from there.
