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#264337 - 06/22/09 09:05 AM Grounding and hum
MarkSJohnson Offline
shareholder in the making

Registered: 09/27/04
Posts: 10966
Loc: Central NH
I read an interesting article in MIX magazine this morning and found it on their website: Mix Interview: Arthur Kelm (A WELL-GROUNDED APPROACH TO AC POWER PROBLEMS).

Although his background is more in recording studios, the information would be helpful to those with hum and grounding issues in their HT.
_________________________
::::::: No disrespect to Axiom, but my favorite woofer is my yellow lab :::::::

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#264350 - 06/22/09 12:57 PM Re: Grounding and hum [Re: MarkSJohnson]
tomtuttle Offline
axiomite

Registered: 06/20/03
Posts: 8305
Loc: Tacoma
So, since you can't solve your square room problem, you're now solving problems you don't even have.

Rock on, Mark.
_________________________
bibere usque ad hilaritatem

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#264358 - 06/22/09 07:32 PM Re: Grounding and hum [Re: MarkSJohnson]
a401classic Offline
connoisseur

Registered: 11/29/06
Posts: 1194
Loc: Alpharetta, GA
I was a little miffed when I got to the $4500 Fluke meter as the beginning of a solution to bad wiring; I'll take the band-aid approach for that kind of coin, thank you very much.

Then I read on and really liked the 220V step-down transformer to 6 outlet idea. Boy, could I have used that that when rewiring. I could have had the entire AV room on a single, isolated circuit...

Oh well, so far I'm passed the hum and buzz portion of the process, so I'm not going to go back and retro-fit.

Scott
_________________________
Scott

My HT

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#264642 - 06/26/09 01:23 AM Re: Grounding and hum [Re: a401classic]
Foobarred Offline
frequent flier

Registered: 06/23/09
Posts: 14
Since we are on the topic...

What level of hum is considered a real ground loop problem? Since I've introduced a separate amp (Newcastle AM-9080) I've noticed a hum at the speakers that wasn't there before when just using my AVR (Onkyo 806). I tore my system apart to isolate the issue last night and traced it back to a few sources.

1. Coax digital input from HTPC to AVR (now acting as a pre/pro).
2. HDMI input from HTPC to AVR (yes, there is a common well-known theme here baout PCs and EMI/RFI)
3. HDMI input from TivoHD DVR.
4. HDMI output to TV/Projector

Now, the hum is really low. You can only hear it if you are within about 6" of the speakers (M60s). When I remove the HTPC connections and the coax from the DVR the noise level drops to almost imperceptible but barely there. I've already ordered a Cable ground loop isolator, and will replace the coax digital from the HTPC with an optical connection, but there really isn't that much I can do about the remaining HDMI connections.

So, what is considered a ground loop problem? A loud (audible from a distance >1 ft.) hum or any hum at all?

It definitely isn't the amp. I tested the noise floor by hooking up an iPod directly to the inputs as well as the AVR with a single optical input connection then standard interconnects to the amp and both test show zero noise...

Thoughts?

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#264645 - 06/26/09 01:28 AM Re: Grounding and hum [Re: Foobarred]
Foobarred Offline
frequent flier

Registered: 06/23/09
Posts: 14
Forgot to mention... All my gear in the HT run back to the same ground on the same circuit...

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#264647 - 06/26/09 01:56 AM Re: Grounding and hum [Re: Foobarred]
grunt Offline
connoisseur

Registered: 12/04/06
Posts: 3569
Loc: Nirvana
If it’s not bothering you from your closest listening position I wouldn’t worry about it. AFAIK ground loops exist to some degree in all our systems it’s just a matter if it’s loud enough to be a problem.

Based on what you’ve said it sounds like your TV cable my be the worst culprit and it sounds like you’ve already moved to solve it.

I had ground loop problem between my subwoofer and DirectTV antenna that I resolved by routing the antenna coax through my Trip-Lite surge suppressor. Here is a link that might offer some help if not I’m sure someone else will have better advice.

http://www.epanorama.net/documents/groundloop/index.html
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3M80 2M22 6QS8 2M2 1EP500 Sony BDP-S590 Panny-7000 Onkyo-3007 Carada-134 Xbox Buttkicker AS-EQ1

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#264651 - 06/26/09 07:25 AM Re: Grounding and hum [Re: Foobarred]
MarkSJohnson Offline
shareholder in the making

Registered: 09/27/04
Posts: 10966
Loc: Central NH
Your situation seems to mirror what the article mentioned: A little here, a little there adds up through the chain.

If you have to be 6" away to hear it though, I wouldn't worry about it.

On my pretty busy small-city street, if I have less than 70dB of ambient noise, I'm happy. In my case, I could have a good hum (insert joke here) and never hear it anyway.
_________________________
::::::: No disrespect to Axiom, but my favorite woofer is my yellow lab :::::::

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#264666 - 06/26/09 11:00 AM Re: Grounding and hum [Re: MarkSJohnson]
Foobarred Offline
frequent flier

Registered: 06/23/09
Posts: 14
Thanks for all the input guys.

Here's an update: I wandered out to the cable drop to check out the grounding on the cable coax. I found the grounding block... and notice that while they hooked up the coax to the grounding block, and ran the grounding wire through it, they didn't bother to screw down the binding post screw!!!! The grounding wire was barely touching the body of the grounding block. So, I tightened the screw and that killed almost all the hum coming from the coax.

I'll probably try the isolator since I've already ordered it to see if it helps any at all on top of that.

I still have to go deal with the HTPC though, but I think the optical connection will help tame that quite a bit. Those PC switching power supplies and HDD motors are pretty noisy in terms of EMI/RFI. If I have to I may migrate the HTPC to a spare laptop... Running directly off of a DC power source will probably clean up the HTPC a lot.

Mark, I wish you hadn't sent that article! This morning I was calling around to a couple of electricians to get quotes on chemrod grounding posts!

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#264667 - 06/26/09 11:13 AM Re: Grounding and hum [Re: Foobarred]
MarkSJohnson Offline
shareholder in the making

Registered: 09/27/04
Posts: 10966
Loc: Central NH
They send me kickbacks.... \:\)
_________________________
::::::: No disrespect to Axiom, but my favorite woofer is my yellow lab :::::::

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#264670 - 06/26/09 11:45 AM Re: Grounding and hum [Re: Foobarred]
alan Offline
connoisseur

Registered: 01/29/02
Posts: 3191
Loc: Toronto/New York/Dwight
Hi Foobarred,

I'm glad you've mostly solved the hum problem. You shouldn't have any audible hum from your speakers or subwoofer, even listening up close. And ground-loop troubles are almost always traceable to TV-cable inputs.

Those chemrod grounding posts are exotic! New to me.

Regards,
Alan
_________________________
Alan Lofft,
Axiom Resident Expert

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