Component grounding

@atmasphere -- That's starting to seem to me like a likely explanation also. Plus the fact that the hum begins when the interconnects are inserted, not when everything is simply powered on. But I really didn't do anything to the DAC except switch the fuse. I'm very careful when doing any kind of operation with my equipment, and as I said earlier, there is no hum with the other two integrateds. One is a solid state, the other a tube.

I installed the nylon washer between the chassis and the ground wire ring. Then a ground washer screws against the ring. Is it worth trying another nylong washer between the ring and the ground washer? 

I installed the nylon washer between the chassis and the ground wire ring.

That doesn't sound right! If there is a connection to the chassis (and I'm assuming it comes from the center pin of the IEC connector) it would not be insulated from the chassis by a nylon washer!

Am I misunderstanding?

I wish I could post a photo of what I mean. If you follow this link to page 7, it talks about a ground wire running from a grounding block on the floor of the chassis to a screw on the side of the top cover. Before you can do anything internally, you have to disconnect this wire from cover; otherwise you can't get the cover out of your way. So, what I did, I put a nylon washer between this wire (which has a ring termination) and the chassis. Then a ground washer goes onto the end to screw it all down. Does that make sense? 

OK, I can't post the link. Anyway, it doesn't say more than I just said. 

I installed the nylon washer between the chassis and the ground wire ring.

Perhaps the wire should be next to the chassis and the nylon washer placed on top of it - and not in between the wire and the chassis?

I am assuming it is a metal screw?

Seems strange to put a piece of nylon (an insulator) between the chassis and the ground wire - but I guess the screw should make the connection

What DAC is it??? - so we can look at the manual

Regards - Steve