I have an issue with my Rotel RB-1090 amp. I recently picked up a Rotel preamp to run it and until now I have been using the balanced (XLR) in's running from a pro audio interface with balanced outs. It worked fine this way. Today when I got the preamp I disconnected the XLR's and connected the unbalanced (RCA) inputs to the preamp AND switched the input selector to on the amp to "Unbalanced". I got a hum out of the speakers. I tested the pre with another amp and it is working fine and clean. So in troubleshooting the amp does not hum with either nothing connected or RCA's connected but as soon as I connect the preamp or other source I get the hum (with the switch on "unbalanced" of course). I also tried different cables with the same result. Running the source component with the preamp with headphones is also clean.
Would it be possible the unbalanced in's are fried but not the balanced ins?
Any help would be appreciated!