I have a 3 channel dual recto and I notice that turning the output knob all the way down didn't cut the sound. I then noticed that turning the solo knob did affect the volume, but the solo button on the footswitch wasn't activated. I have the loop active in the back so the solo function should work only when it is selected but now the solo and output knobs are both acting as master volume. This has never happened in the 3 years I've had the amp. And the solo function was working perfectly this weekend. Any ideas? I'm totally stumped here. Tubes look fine and the amp sounds great otherwise.