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#326711 - 10/27/10 12:19 PM Ground loop with new receiver
amilkey Offline

Registered: 10/27/10
Posts: 2
Hi All,
Been an Axiom user now for about 6 years and still really like them. I decided to treat myself to a new receiver. I purchased an Onkyo TX-NR870, I connected my front speakers and then the subwoofer rca cable. The minute I plugged it in I started hearing a soft hum/buzz. This is with the unit off, I then went to plug in the HDMI cable from my Blu-Ray player and the minute the shell touched the chassis the buzz got 10X worse. I checked out the sub and found the RCA input jack to be a bit loose. I opened the sub and resoldered all the connections which didn't help. The sub does not buzz with my old reeiver so I'm assumign it's the receivers grounding issues. I spoke with Onkyo service and they said to return the unit. I did and the new unit does exactly the same thing. Any idea's? I tried lifting the ground on the sub power cable and it only made it worse. On another note when I opened up the sub - the plastic casing completely fell to pieces like the plastic is dry rotted. The plastic is so brittle that one touch breaks it off...Any help would be greatly appreciated.

#326713 - 10/27/10 12:25 PM Re: Ground loop with new receiver [Re: amilkey]
EFalardeau Offline

Registered: 08/27/07
Posts: 3400
Loc: Laval, Quebec, Canada
Simply locate and unscrew (just a few turns, no need to remove completely) the "ground screw" at the back of your sub. That should do the trick. I have had Onkyo receivers and i've always ran into that kind of problems with sub and also when used as pre/pro for separate amp.
E = MC2 = ((2M80 + VP180 + 4QS8)/(EP800 + EP500))^(ADA1500 x D2v)

#326719 - 10/27/10 12:54 PM Re: Ground loop with new receiver [Re: EFalardeau]
jakewash Offline
shareholder in the making

Registered: 12/26/03
Posts: 10420
Loc: Calgary, Alberta
Also try using the same plug in for all the components, receiver, sub, TV, SAT box, etc. and see if that helps. Conversely use a different plug in for all and see if that helps. There is a product avaiable, ground loop isolator that may also help your situation. Ground loops are lots of fun to track down and remove.
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70

#326744 - 10/27/10 04:11 PM Re: Ground loop with new receiver [Re: jakewash]
Capn_Pickard Offline

Registered: 03/09/04
Posts: 1056
Loc: Arlington, VA (NOVA)
Also try isolating the cable signal. I had a ground loop caused by my cable connection. Running it through a power strip solved my issue.

Just to be sure, also try swapping out the cable from the amp to the sub to confirm it's not a loose (or bad) wire.

#326767 - 10/27/10 10:11 PM Re: Ground loop with new receiver [Re: Capn_Pickard]
amilkey Offline

Registered: 10/27/10
Posts: 2
Thanks for the recommendations. I have the EP-500 sub. I do see a screw hole that says "Chassis Ground" but there is no screw in the hole and it really doesn't look like there are any threads in it... Kinda wierd I will look into further.
I will also try the recommendations above before purchasing the loop isolator.

#326768 - 10/27/10 10:19 PM Re: Ground loop with new receiver [Re: amilkey]
Jc Offline


Registered: 06/27/06
Posts: 531
Loc: Sherbrooke, QC, Canada

The chassis ground screw is a 3mm x 10mm screw. You can be sure that there are treads. Simply screwing a screw back in place might solve your issue.

#326769 - 10/27/10 10:23 PM Re: Ground loop with new receiver [Re: Jc]
terzaghi Offline

Registered: 04/04/07
Posts: 4872
Loc: Tulsa, Oklahoma
Hmmm, no screw at all? contact axiom and have them send you one if it is really missing. screwing it in will likely not solve the problem (unscrewing it usually does the trick) but you should have a screw there so you have the option of screwing or unscrewing it.

Do you have cable TV service? I had a ground loop from my cable line and purchasing the axiom ground isolator did the trick.

#326771 - 10/27/10 10:28 PM Re: Ground loop with new receiver [Re: amilkey]
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10644
AM, welcome. Among the puzzling points in your report is the "lifting" of the ground on the sub power cord. What did you specifically do? Without the sub being grounded through the cord there wouldn't be a path to form a ground loop through the sub amp.

Enjoy the music, not the equipment.


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