I haven't been able to get my pre-pro back to verify that it's still the case, but if this hum is the same as it was before I sent it in for repair, which I assume it is, then no, the balanced connections didn't make a difference. I know when I first moved to balanced connections, noise did seem to be reduced.
That's interesting about the RCA-to-XLR adapters. JC was saying that if balanced connections defeated the hum before, then it would be possible for those adapters to do the same thing. I didn't see how. This would confirm that balanced connections wouldn't help, though, since I'm using the adapters now, and the hum is as strong as ever.
Actually, the only thing JC suggested I try was the balanced connections, if possible, and I explained how the hum had been present when I was still using them, and it persists with the RCA-to-XLR adapters. I think the things you guys have had me try has helped me head off some of the suggestions he would have made.
He'll be forwarding the stuff I've tried to Andrew, and he'll try to help me pinpoint the issue. Based on the hum being absent without any inputs hooked up, and the amount of hum changing based on whether it was the receiver sending the signal or the portable player, Andrew said they could likely rule out the amp as being the issue. His theory was a ground issue of some sort. JC still has more details to forward, so we'll see if that changes.
