Hi, I bet this is a stupid question, but I could never figure this out. On the back of my cab (Ampeg 410HLF) There is a knob that says "Level Control" and it has numbers going around it clockwise going from 20 down to 1. The numbers become more widely spaced as they go aroung clockwise. I thought that maybe it was a volume control, but when I turn it while I play, the volume does not change. Because of this I have never used this knob, I have just left it at 12 O' clock. I'm sure all you techies know what this does. What does it do? Is it important?