Thank you all for the suggestions! They gave me a simplified path to further isolate the problem. Here's the current status:
@imhififan Swapping positions of the 2 units had no effect. Had tried that before I posted yesterday. 60 Hz hum equally audible either way.
@oldhvymec The Denon has a polarized 2 prong plug and by electrically isolated, I mean everything at the line level is plugged into the same power conditioner. RCA cables are all shielded with the Denon using a matched pair of older Monster directional cables (output only) and the TASCAM two pair of new Mogami (don't have a pair of XLR input connections left on my preamp to use those instead).
@millercarbon Moving the Denon about 3 feet away from the TASCAM eliminated the noise, and it stayed eliminated whether the Denon was powered through the conditioner or via a totally different circuit.
Finally, the 60 Hz noise is there regardless of whether the RCAs are connected to the Denon and the only thing that eliminates it is moving the deck further away from the TASCAM.
So unless this update spurs another approach, I'm going to deploy the advice from @mijoystn and @millercarbon next. Getting a piece of magnetic steel is both easy and inexpensive as is screwing a ground wire down to it.
Thanks again and I'll post a follow-up once I've had a chance to to try the steel shielding out.
@imhififan Swapping positions of the 2 units had no effect. Had tried that before I posted yesterday. 60 Hz hum equally audible either way.
@oldhvymec The Denon has a polarized 2 prong plug and by electrically isolated, I mean everything at the line level is plugged into the same power conditioner. RCA cables are all shielded with the Denon using a matched pair of older Monster directional cables (output only) and the TASCAM two pair of new Mogami (don't have a pair of XLR input connections left on my preamp to use those instead).
@millercarbon Moving the Denon about 3 feet away from the TASCAM eliminated the noise, and it stayed eliminated whether the Denon was powered through the conditioner or via a totally different circuit.
Finally, the 60 Hz noise is there regardless of whether the RCAs are connected to the Denon and the only thing that eliminates it is moving the deck further away from the TASCAM.
So unless this update spurs another approach, I'm going to deploy the advice from @mijoystn and @millercarbon next. Getting a piece of magnetic steel is both easy and inexpensive as is screwing a ground wire down to it.
Thanks again and I'll post a follow-up once I've had a chance to to try the steel shielding out.