alcarp said
I'll certainly try those things. Meanwhile, does the fact that I get no hum using the Rotel power amp suggest that the DS or inputs to the DS may not be the problem or is that an over-simplification?
Groundloops suck. Much of the time no particular device is at fault - they just happen and are difficult to eradicate with our more and more connected world/audio systems.
You could unconnect everything then start at the amp with nothing connected to it, if there’s no sign of hum then connect one input, but have that device have no inputs, see if there’s a problem yet, … When you add something that causes the loop you’ll know a little more than you do now. But that loop could be to anything that’s already in the system…
Frode’s idea is a good one if you can’t fix it in a simpler way, say by plugging into different outlets or turning non polarized plugs over…
The Jensen Transformers web site has a lot on diagnosing hum and fixing it.