Despite that the balance is set to neutral (middle) the right channel delivers clearly lower audio than the left channel for all I/O. I didn't try with headphones directly from the amp. The amp is Sony STR-DE515 and the speakers are B&W DM601. Is there a way to measure where the drop is?
I switched the cables to see whether the fault was the speaker and it isn't. Switching the cables swiches the fault to the other speaker. So the fault is the amp or the cable(?)
The troubleshooting leads to the conclusion that the amp is faulty. So how can an amp lose 75 % of a channel instead of everything?