Was there water in the pipe? If so, it was probably a relatively low resistance ground to mother earth, unless the pipe had no water in it.

Not suggesting it is ideal though

Yes, there's no hum when the rack is powered by the outlet next to the rack without the UPS. It does, however, hum obnoxiously when plugged into outlet in other room.


I did try unplugging everything but power to the preamp and amp, started adding things one at a time, power first (DirecTv AV genie then Oppo blu ray, PS3 and finally a Denon AVR for Zone 2.). As soon as I start connecting HDMI cables the buzz starts. The Denon seems to add the most.

The rack has a dedicated 20A circuit. Everything including the projector is powered from the rack. The "other room" is really just the hallway which is on some other electrical circuit which may include some incandescent lights, but that's about it. There is nothing else running besides furnace and it's on it's own circuit.

Agreed, Looks like I should look a little closer at the house wiring. No reason the system should have a problem ANY circuit if it doesn't have a problem on one.

hahahahaha

Since you are dealing with an ups. Have you tried with it unplugged from the outlet? So that the UPS is providing a "clean" source of power? When the UPS is powering the system, does the hum still sound?

KOT

Oh my... never considered that, great idea.


Good one, but what's funnier is...


Great advice Buzz, but your not welcome here.

try swapping the breaker in the electrical panel to the opposit phase. this should be easily accomplished as long as the panel is not full.

That would be great troubleshooting. But this statement by the OP kinda scares me from that idea.


If, you Freddy, are able to swap the circuit to the other phase and the hum goes away. Or gets louder. Then might I suggest turning one breaker off at a time. After each switch off, listen for the hum. Hopefully one of the breakers will cause the hum to go away. If so, then whatever is on that particular circuit is causing the hum.

KOT

That's common, but my satellite equipment wasn't even grounded by the installers- I called DirecTV and told them it needed to be grounded properly and they came back for that because I asked if they wanted me to quote the NEC article I was holding in my hand.

The first thing I would do is have the electrical service checked for wiring errors and grounding. It's possible that someone added outlets and didn't follow code. It's also possible that grounded outlets were installed and a wire broke inside of the junction box and the lamp connected to it still works. Once that's done, I would try a different APC to see if that has an internal problem. This should be obvious- it will make noise with one and not with the other.

The projector was said to be on the same circuit as the rack- has anyone proved this, or is it assumed? I would insert a circuit tester in the projector's receptacle and turn off the breaker for that room- if the tester shows power, it's a ground loop in that room. The fact that it's louder when the extension cord is used could mean  the cord may have a problem causing more voltage drop or the other room's wiring is bad. If that room and the EV room share a grounding point outside of the panel will cause this and when conduit is used, sometimes the hot and neutral are fed without making sure the ground to the panel is 'unbroken'. Sometimes, the neutral is omitted and the one from another room is used when the conduit is so full they can't pull a new one and in some cases, the conduit is the ground conductor and the screw on a coupler is loose or corroded- it only takes one to break the ground.

Doesn't this indicate that the noise is being introduced by the APC? If any of the other electrical issues mentioned caused noise wouldn't that noise also be present without the APC? Is the APC grounded to the rack? Can you isolate it from the rack(no screws)?

No water, or earth. The cut away, isolated section of pipe was not so neatly tucked up under the floor joists.

Pure water is not a very good conductor. Dry earth is not much of a conductor either. Minerals dissolved in water enhance the earth's conductivity.

Minerals dissolved in water enhance the water's conductivity even more!

I was there today and low and behold, hum IS present when the system is running on the APC's battery power. It has a slightly different sound but same intensity. Hum goes away when everything gets powered by the naked wall outlet.

Also, to those of you who were asking if I know the projector is on the same circuit. the projector is powered by a power INLET, twist and lock, above the rack where the line feeds into the outlet at the projector, so yes the projector is powered directly from the UPS.

Lastly FWIW I ran an extension cord back out to the hallway outlet and again got awful hum from that naked outlet. This baffles me because this is an everyday 3 bedroom house and never once Have I not been able to use whatever outlet is around to power my system and not have a buzz that was not related to the cable company's grounding.

Once again, when the system is powered by its own naked power outlet without the UPS it works perfectly.

I should've asked to have you have the UPS power the entire system. And if hum was present, as it was, then unplug any cable that is coming in from the outside. For example the cable for cable TV, CAT-5 cabling or anything else that is "foreign". Basically make the entire system run off of the UPS. If the hum it still present there, then it's most likely in the UPS. If it's not, then plug each of the foreign cables one at a time until the hum comes back. Then verify it's that particular cable, or a combination of the cables.

I am baffled by the fact that with out the UPS and it plugged into the room next door, the hum is present. But there again, this is why I stated the above for the foreign cables.

KOT

Be sure to check to see if there is an unexpected ground associated with the projector. (perhaps in its mount)