Group loop hum....

[shenandoah75]

Well, i am sruggling with ground loop hum in my whole house setup (at least that's what i think it is)... I'm still trying to debug, but so far a few things i found before i got too tired last night:

1) if i bypass the onkyo receiver and go from PC audio -> WH amp, i'm ok
2) if i remove everything else from the onkyo, i'm ok (this must include removing the in/out HDMI connections to tv/cable box). Plugging either in creates an issue
3) removing the cable line from STB doesn't remove it

Note all equipment is the same crcuit and going through an APC UPS...

any tips?

of particular confusion to me are:
1) the fact that te noise is transferred at least in some cases over hdmi (even to tv only when it is unplugged from outlet/ground)
2) some of the device initiating the noise don't have a ground (namely the STB) - i.e. drop the cable line and there's no potential for grounding to anywhere else since the plug connects to only hot and neutral...
3) just curious why the onkyo itself is not grounded. all the proaudio stuff i've ever worked with grounds all the equipment. This has the shape of the stand IEC? plug, but gournd pin is removed...

thx in advance for any help!
-brad

 

[TCassio]

I have a Sonos Whole house system, and 1 of the zone palyers were connected to an Onkyo amp and I had a group loop hum. I purchased a ground loop isolator from Radio shack and the problem was gone.

 

[shenandoah75]

hmmm, but what do i do when the source is via an HDMI cable?

-brad

 

[jay]

Do you have another cable to sub?

 

[shenandoah75]

will try...

currently i've got three short runs in the cabinet and a 50' run to the tv... I have another 50'er i can plug in and swap the short lengths around a little.

hdmi out -> Plasma (hum) 50'
hdmi in1 -> STB (hum)
hdmi in2 -> DVD
hdmi in3 -> PC (hum-i think)

The hums come independantly in all cases. i.e. unplug all four, and i plugin any of three noted (save the dvd) and i get the hum in Zone 2 rca output. I don't recall getting the hum in the HT setup though (would hope not since its digital). I need to verify this though for sure. If the hum is only in zone2/3 then the isolators should work.

I've turned off all lighting, etc to try to see if that could be an issue, but didn't make a difference

thx
-brad

 

[Captain Caveman]

What I would do is grab a 50' AC extension cable and plug your AMP into another AC outlet. If the hum goes away then your solution would be to add another outlet behind your amp that is on the circuit that did not have the problem.

If the hum persist then try the AC extension trick on the other pieces of equipment or maybe try a different amp.

 

[huggy59]

Cable is notorious for ground loop issues, too. If you can, try an isolator on the incoming cable to your cable equipment. Years ago this fixed a ton of problems I was having at an apartment complex I lived at.

 

[Sacedog]

will try...

currently i've got three short runs in the cabinet and a 50' run to the tv... I have another 50'er i can plug in and swap the short lengths around a little.

hdmi out -> Plasma (hum) 50'
hdmi in1 -> STB (hum)
hdmi in2 -> DVD
hdmi in3 -> PC (hum-i think)

Are you using an active extender for the HDMI cable to the Plasma, or is it just straight HDMI?

 

[shenandoah75]

straight - monster 400 i think? I actually have 4 of these cables - 2 to the plasma in HT and 2 to my masterbedroom lcd (not using second one on the plasma)

Signal at tvs, etc seems ok as far as i can tell
-brad

 

[linuxha]

I'm not an expert but I have been reading up on this (ground loop hum). One short article I read found that the cable ground block wasn't grounded. It's simple enough to check (usually). He pulled apart each piece of equipment (some was daisy chained) and found each piece reduced the hum a little bit. When he found that the ground block was not ground he eliminate most of it by adding the proper ground.