I’d been chasing a hum/buz for about 3 years, and gave up on trying to find the root cause. Now during an equipment upgrade rewiring effort I’ve decided to try again and I may be getting closer to the problem but need fellow Outlaws to weigh in. (Gonk I hope you’re out there.) I guess it’s best to start with the setup: 990, 7500, Pioneer Elite DV-45A player/SACD/DVD-Audio (I think the culprit), Denon CD changer, Thorens turntable, Panamax line conditioner, and now a new Pioneer Elite Pro 111 Plasma Panel (not yet hooked up).

My cable service is Comcast without a set top box and for the current testing is disconnected at the wall. I am not using the 990 for video switching. The 45A connects with component video directly to the (former) Sony TV. (This is when I discovered that removing the component video connection, the speaker hum went away.)

All power runs through the Panamax except the 7500 which goes to a separate 20A dedicated circuit. The Panamax is on its own 15A dedicated circuit. Again - no cable lines tied in for the current testing. (Cable normally went into Panamax, then to old VCR then to TV.) The 45A is not a grounded plug (only 2 prongs). For the test, I’ve plugged the 45A into both the Panamax and to several completely different outlets, with no change in hum.

As stated above, the speaker hum disappeared when component video was removed between TV and 45A. I then tried connecting s-video between 45A and TV without the component video connected and got hum. So, any video from 45A to TV was a problem.

Now I began to focus on the audio between 45A and 990. The 45A connects to the 990 with 5.1 audio, digital audio and 2 channel audio. With either video lines (component or s-video) between 45A and TV in place, upon removing both the 2 channel audio and/or the digital audio between the 45A and the 990 – the hum GOES AWAY! The 5.1 audio connections from 45A to 990 doesn’t seem to be affected; i.e. they are still connected and the hum disappears with either the digital or 2 channel audio removed. (Are we getting closer??)

My question – what now? Seems the 45A audio section is a problem but short of ditching the unit do I have any other options? Oh, all cables are (do I dare say it) Monster brand so they’re not run-of–the-mill stuff. I am waiting for Oppo to release their new all-in-one HD player, but in the meantime do I look at maybe grounding the chassis of the 45A somehow and would that even do anything? Would love some fellow Outlaw thoughts and/or ideas.

Thanks a bunch.

Certainly a curious little quandary. Are you using coaxial digital audio? If so, I'd try leaving the stereo analog off and running optical between the 45A and 990 - see if that arrangement (with everything else in place) gives you a hum-free condition. I'd also look at the cables being used for digital audio and stereo analog, both their shielding/construction and how they are routed relative to other wiring (particularly 120V power cords).

I'm not an electrician, but this sounds like a ground loop induced hum. While cable TV is the most common source of ground loops that cause speaker hum you still have gear plugged into two different circuits that may be grounded differently. Have you tried plugging everything into either the 20 or 15 amp circuits? If the hum goes away when you do that it may be time to call an electrician to work on the grounding of each circuit. An electrician friend of mine told me ground loops can be caused by something as simple as loose screws on ground wires but it can also be quite an effort to find them.

This is a real shot in the dark, but have you tried running the component video through the 990?
If nothing else you might determine if the hum is present with the Pioneer connected to the 990 but not the TV, or with the 990 connected to the TV but not the Pioneer, in which case the Pioneer is eliminated as the culprit.

Thought I should give an update as fellow Outlaws Gonk, AvFan and KOYANN were nice to offer suggestions. First, turns out I was wrong about one portion of the problem, that being the 5.1 analog inputs being connected then disconnected from the 990 did in fact cause hum to be present when connected to the DV-45. Gonk, I did try your idea and connected an optical audio cable between 990 and the 45 with no other audio connections. There was no hum. While this was good info, I didn't want to lose the 5.1 feature.

I then decided to explore AvFan's ground loop thought further. While I was sure some of these power combinations I'd tried before, since I had the rack apart, I might as well do more trials. Turns out, if all electronics went through the Panamax 5100 the hum was all but gone. Panamax was plugged to the dedicated 20 Amp circuit.

Now enters the Kuro PRO111FD! (Wow what a panel!) Anyway, had everything back in place, and the Kuro going into the Panamax - now another (type) of hum appears! This time not from the speakers but from the 7500! This was different than anything previous, and it cycled up for 5 seconds (loud) then down for 15 seconds then back up for 5 seconds. A very low frequency hum. It was obvious the new Plasma and the 7500 weren't getting along!

GREAT, now what. I pulled the rack out again, (each time having to remove the 7500 as the rack won't roll with it in place), and again tried various circuit combinations with extension cords. I remembered a thread from a while ago talking about the relationship of the house circuits to the bus bars on the electrical panel. After studying my electric panel's circuit layout (200 Amp , 40 breaker panel), I realized all the circuit combinations I was trying were coming off the same bus. I then took the 7500 to a different circuit/bus and kept the Kuro plugged into the Panamax. The new hum went away! As of today, this setup seems to be "holding". Only down side is the 7500 has no protection.

I felt I should share this ordeal with fellow Outlaws as it sure has been a frustrating effort, and hopefully others may be able to avoid similar issues. Look forward to any follow-up thoughts from the gang.