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 Post subject: Help! Speaker/Sub Hum associated with Cable & HTPC
PostPosted: Thu Apr 23, 2009 10:59 am 
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Location: San Diego, CA
I'm getting a lot of humming from my living room surround speaker system, most notably my subwoofer.
I have Sharp LCD TV & Onkyo AV Receiver with inputs from DVD player, CD player, Xbox360, HTPC and Cable box DVR. The problem seems to be associated with the DVR/Cable signal and/or the HTPC.

I can best trouble-shoot it with a DVD playing during a 'quiet scene'. I can then eliminate the hum by
1) disconnecting the Sub (faint hum from still present from other speakers)
2) disconnecting HDMI output to TV (obviously unacceptable)
3) disconnecting the cable from the wall
4) unplugging the HTPC (note, i tried putting it on a power strip but even in the off position, it still hums) or unplugging the audio output.

I have a feeling it is an electrical grounding issue... but I don't really know how to approach a fix.

My HTPC was recently upgraded from onboard digital Coax sound to a PCI sound card for surround. Since then, it seems to have gotten worse in that now I also get the hum when watching cable TV & DVDs. I've tried physically separating the cables the best I could, with no improvement. Also I've tried plugging the HTPC in with an outlet from another room, to no avail.

I've had the cable guy out twice, but they seemed to have no idea what could cause such a thing, and were unable to offer a fix.
There are a number of suggestions from various online forums, most seem to point to getting an in-line ground loop isolator; ~$50.
http://www.axiomaudio.com/groundisolator.html
I'm not thrilled about the cost, and I'm worried about potentially degrading the incoming signal? or it not fixing the problem!

I didn't see any discussions on this topic at spcr, and thought it would be good to get some input.
thx!

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 Post subject:
PostPosted: Fri Apr 24, 2009 9:32 am 
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Location: Finland
Sounds like ground loop to me. One thing you can get is a surge protector that has plugs for cable too, then route all cables to the audio setup through it.

The thing is, tv sets are usually grounded by the cable, amps not at all, and PCs from the power outlet, and the cable ground can be at a different potential than the power outlet ground. The surge protector will make the cable ground be equal to the power outlet ground.

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 Post subject: Surge Protector vs. "Power Centers"
PostPosted: Mon Apr 27, 2009 9:59 am 
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Location: San Diego, CA
Do I just need any surge protector with coax pass, or should I get one of those fancy "power centers"? i.e. from Monster.
They claim to 'clean' the power and enhance video & audio. But there seem to be a lot of mixed reviews from consumers, and I haven't seen ANY professional reviews. These also can come at quite a cost, upwards of $300!!

Would SPCR consider weighing in on the benefits of 'conditioning' incoming AC power? I don't see anything in the forums currently!

http://www.monstercable.com/power/Monster_Power.asp
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#1) Antec P182 SE; Asus M2N-e; AthlonX2 6400+ BlkEd; 4x1gb Corsair XMS2; Zalman 9700; MSI 8800GTS OC 512mb; Enermax Liberty 620W. WD 74gb Raptor (boot).
#2) Antec P182; Asus M3a; Phenom 9900 2.6Ghz; 2x1gb Crucial pc6400; Scythe KatanaII; XFX 8800GTS 512mb; Antec Phantom 500Watt; WD 74gb Raptor (boot).
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Last edited by bkoehn on Tue May 05, 2009 8:13 am, edited 1 time in total.

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 Post subject:
PostPosted: Mon Apr 27, 2009 12:12 pm 
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Location: Monterey Bay, CA
+1 on a surge suppressor as the single point ground.

Monster makes money off of hype. You can probably find a $20-30 outlet that provides cable, phone, 6+ AC outlets, surge suppression, EMI/RFI suppression. APC, Belkin, Tripp-Lite, Cyberpower, etc. are shown at newegg.com. Or, try your local Fry's.

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 Post subject:
PostPosted: Mon Apr 27, 2009 4:15 pm 
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Those things are worthless for grounding issues, IME. Or vastly overpriced.

http://www.tripplite.com/en/products/mo ... delID=2814
This company makes the real deal, IMO, at least short of special per-outlet blocks.


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 Post subject:
PostPosted: Mon Apr 27, 2009 4:45 pm 
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bet all you need is a ground loop isolator on the sub input.
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 Post subject: Eureka!
PostPosted: Mon May 04, 2009 9:01 pm 
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Location: San Diego, CA
The in-line Coax surge protector worked GREAT!
Well worth the $20 investment.
Note, the hum wasn't isolated to the sub only (though most noticeable there), so I don't thing a "ground loop isolator on the sub input" would have worked.

cheers!

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#2) Antec P182; Asus M3a; Phenom 9900 2.6Ghz; 2x1gb Crucial pc6400; Scythe KatanaII; XFX 8800GTS 512mb; Antec Phantom 500Watt; WD 74gb Raptor (boot).
Buffalo Terastation -RAID5- 750Gb NAS.


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 Post subject:
PostPosted: Tue May 05, 2009 7:06 am 
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Excellent. :D

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 Post subject:
PostPosted: Tue May 05, 2009 7:23 am 
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Glad to hear this worked for you. I had a similar issue when I first picked up a cheap sub amp for a custom subwoofer I was making. At the time, I was using a shuttle SFF PC. Only got the noise when the Coax SPDIF audio was connected to the stereo. I found that grounding the actual shuttle case helped. I've since killed that thing and my new Antec NSK1480 case doesn't appear to have this issue as it uses a standard PSU that is itself grounded as opposed to the Shuttle which had an external DC brick. But I do notice the TV signal gets a little fuzzy when the HTPC is on. So I think I'm still getting some grounding issues. I'll have to try this.


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