Hi TalkBass, Just received a used Aguilar AG500 (2 channel) from eBay. Noticing the Master Volume on Channel 1 is goofed. Turning the Master Volume knob makes no change in the volume. It seems to be 'stuck' at a fairly high level, despite where I turn the knob. However, if the Master Volume knob is turned all the way down to where 0 would be, the sound is very scratchy and fades in and out (while still at the same semi-loud level). Any ideas what this might be? Thanks!