Sorry to hear that.yes, my money is on AC as well..........and it's a royal pain in the ass...anything AC related...
for the amps any change doesn't matter as you have rebiased the amp to your voltage. leaves other components.
Dead giveaway is if the sound changes equally in both channels. Then it's a component. For example, such a drastic change is possible within the amp, but if both channels do the same, then it's also very unlikely.........as always, call me,
Klaus