This morning when my amps came to life I was presented with an atypical hum that I traced to my phono preamp. After remaking all connections and restarting it, the hum was still there.
Eventually I restarted everything by restarting the P20. The hum was gone but for less than a minute.
I plugged the preamp into the wall and dead silence as normal.
Plugged back into Zone D and hum. Plugged into any other Zone and silence.
How could one zone outlet become problematic? It’s just wire at that point, is it not?
Hmm, sorry this is happening to you, Ron. I’m going to stay tuned in to see what happens.
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Thanks Tony. The system is playing normally now with the zone D outlet unused. But I am worried about what’s next.
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It must be unsettling to have this going on. If it were a modern automobile I’d say you forgot to pay your yearly subscription for zone D, lol. I imagine that the phono pre is the most sensitive to ground loop. Does zone D successfully power your other equipment? If I were in your shoes it’d be nice to know if the failure is isolated or if it has the potential to spread. Have you called support to see if they are familiar with this type of fault?
I haven’t called yet but I will later. I can’t think of how it can be a ground loop based on the construction of the p20.
If the plugs contact(s) go bad, and lift the ground, it can make a ground loop. Plugs are wear items. Easiest thing to blame.
Galen
I guess theoretically that could happen. But except for annual maintenance, that cable has been plugged into that receptacle undisturbed for years.
Bet the plug is fine. Buy one of these and find out.
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Thanks, I will.
Start easy, go to harder. You have a lifted ground and what ever it is it happened just sitting there, too. Take a VOM and measure the voltage at the plug(s). The no load value should be identical. One a load is put on the device under test, with a bad connection, you’ll see a difference. The plug eats some before you get what’s supposed to be provided. Same as a battery’s internal resistance going up as it ages. No load is the reference volage but load is the working after everything in series get’s it’s voltage drop factored in.
My M40 HV amps tube socket cracked just sitting there over a year. All sort of weird stuff can go on. The complex seeming problem was an intermittent socket contact.
Galen
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The hum was present again this morning. I restarted the P20 and it came back quiet and according to the display, the distortion in and out numbers look normal.
I looked up when I put it into service: 2018, August. It’s been operating almost continuously for 7 years or roughly 60,000 hours. I think it’s time for it to go back to Boulder for points and plugs.
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A friend let me borrow his Shunyata Everest over night. I was VERY sorry to see it go just now.
It could be that my P20 was aging at a slow enough rate that I didn’t notice it. But the Everest sounds amazing; I could live-happily-and-move-on-with-it amazing.
So what you are saying is that there are options…
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Options yes. My wife would say “a 15,000 dollar option is not an option.” 
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“So, you’re saying there’s a chance.”
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I didn’t know, so i looked it up. It is $15K! I thought you were joking.
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Aside from the sonic advantage it is passive, so less worries down the road.
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PowerZone time???
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A little bird told me lack of finances prevents consideration. Something about assisting funding his son’s recent home purchase.
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Damn bird gets around…
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