On December 10, 2014 at 20:38, highfigh said...
What is in the system, but not plugged into the APC?
On December 11, 2014 at 00:47, FreddyFreeloader said...
...Only exception might be a Unifi wifi access point POE injector sharing the duplex AC outlet the APC is plugged into. Ethernet cable from Poe injector plugged into switch in rack.
While this should not be a problem, you also should not have hum, so look into things that should not be problems!
I have tried lifting ground on individual components (not all at once and just audio components and projector) with no luck.
So you didn't unplug the video components, such as your satellite receiver, cable box, DVD, game, Roku, etc.? Just the CD player and the dual cassette? An actual list of what you've got, plus a list of what's not in the same room, might be helpful.
FWIW you can also get rid of the hum by unplugging all HDMI cables from the Marantz. Each individual HDMI cable, when plugged into the AVR individually, produces a smaller amount of hum so I couldn't seem to isolate it to a certain path. When they're all plugged in is when it was the loudest.
Really strange! I think you should follow the advice regarding grounds and neutrals in the house. This is a very squirrely problem!
In passing let me note that every system has oodles of actual ground loops. A CD player with analog connection has a ground loop between the two channels. The thing is, we never think about what ground loops exist until we have hum, and then we ignore the mass of such connections, making it hard to find the problem.
One last thing I would like to mention that was strange, is that when troubleshooting and looking at at the APC, I started off by bypassing it and plugged an extension cord straight into an outlet in a different room and for some reason the hum got like 10x louder. Tried it back in the dedicated outlet for the rack and it cleared up completely. Wonder what was up with that other circuit and if it's related at all to to my problem.
Well, yes. But when you connected to power in the other room, was ANYTHING else in the system connected to power? From what you've described so far, you have a projector and a system in one room with no leads running to any other room at all; it's important to know about that. This latest hum source seems to be interaction between the ground in that other room and some other ground the equipment is connected to... but you haven't actually described all the wiring.
On December 11, 2014 at 08:25, thecapnredfish said...
Could you explain how these are improperly grounded.
The cable system goes all over the county, and for it to work properly it must be grounded at multiple points, the nearest one to you being at the cable demarc on your property.
Let's say the cable system is grounded at the pole, but at the pole there's a heavy imbalance of power being drawn by a couple of other houses. The nearest power transformer is grounded; the cable is grounded at the same location; but because of the neutral current due to the imbalanced load of other people, that ground is actually several volts above ground. Then the cable comes to your house and is not connected to a ground at your house. The shield then has several volts of AC on it, which are injected into your system when you connect the cable.
Even if you don't understand this, when troubleshooting hum the FIRST thing you should do is disconnect ALL cable feeds, satellite feeds, antenna feeds... as these may or may not have grounds and you won't know.
