Subwoofer Hum from HTPC - AVS Forum
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post #1 of 16 Old 02-16-2013, 06:06 PM - Thread Starter
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I have isolated my Ground loop hum in my Home Theater system to the HTPC.

The pc is connected to the receiver through the video card using a DVI/ HDMI adapter with an HDMI cable.
If I unplug the HDMI cable from the receiver the hum stops. All devices are plugged into the same Grounded power strip.

I have attempted connecting an spidf cable to run the sound to the receiver and this works only when I unhook the hdmi cable. which kills my video. So its definitely the HDMI connection to the receiver from the Video card.

Any suggestions on how to stop this hum?
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post #2 of 16 Old 02-16-2013, 09:03 PM
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Have you tried a different HDMI cable?

You don't need a $100 "Monster" but don't assume yours is good without checking it.

BTW, if you don't have a cable laying around to check with, there are DVI-HDMI cables where you would
be checking both likely culprits.
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post #3 of 16 Old 02-16-2013, 09:05 PM - Thread Starter
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I have actually tried 3 different HDMI cables.
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post #4 of 16 Old 02-16-2013, 11:07 PM
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I had subwoofer hum caused by a cheap coax going from the AVR to the subwoofer. It appeared to be picking up 60 Hz from the nearby subwoofer power cord, and the low level 60 Hz signal was enough to keep the subwoofer powered on even though the AVR was turned off. When the AVR was turned on there was no hum. So the coax must have have been grounded when the AVR was on, but not when it was off.

As I moved the subwoofer coax further from the power cord the hum decreased. Using a better shielded coax solved the problem. Obviously that may not be your situation but you might want to investigate that possibility.
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post #5 of 16 Old 02-16-2013, 11:10 PM - Thread Starter
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I have tried all possibilities and it's definitely the hdmi connection with the video cable everything else is just fine.
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post #6 of 16 Old 02-17-2013, 04:36 AM
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Sounds like the ground loop could be PC to AVR. Try running a conductor from your PC chassis to the AVR chassis and see what that does.
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post #7 of 16 Old 02-17-2013, 06:31 AM
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I realize you said "tried all possibilities" but that is kind of vague. The idea is to leave the hdmi link in place and remove all other connections - like reconfiguring your avr to not use a subwoofer - put your front speaker setting to "large" so that they will hum at 60hz instead of the sub. That way you can completely disconnect the sub and rule it out. Also pull any other connections, especially coax for cable-tv/radio and ethernet. Really strip it down to the absolute bare minimum of:

power for htpc
power for avr
hdmi cable between htpc and avr
front l/r speakers to avr (assuming these are passive speakers that do not require power from the wall)

and nothing else - not even that power-strip, just use the two outlets on the one wall socket. If it is still humming, then I think you are SOL. If it is gone, then add back one connection/device at a time until the hum comes back.

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post #8 of 16 Old 02-17-2013, 09:46 AM
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You could also try a cheater plug on the avr or htpc.

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post #9 of 16 Old 02-17-2013, 01:46 PM - Thread Starter
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I have attempted to strip it down, this issue has been going on since I built this HTPC which was 5 weeks ago.

Basically I can have every device plugged into my receiver without any hums at all. I can play music from my phone, and dvd player, and through the cable box. All without any hum at all. I have the cable line grounded to the same power strip as the receiver, sub, tv, and all.

Then I take the HTPC and plug it in. As soon as I plug the HDMI cable from the HTPC to the reciever the hum starts. I have tried plugging the HTPC into the same power strip, and a separate power strip.

I know its coming from the HTPC and the only way to connect the HTPC to the receiver is through the HDMI port so I can get video.
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post #10 of 16 Old 02-17-2013, 03:09 PM
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Quote:
Originally Posted by Psyotik View Post

I have attempted to strip it down, this issue has been going on since I built this HTPC which was 5 weeks ago.

Basically I can have every device plugged into my receiver without any hums at all. I can play music from my phone, and dvd player, and through the cable box. All without any hum at all. I have the cable line grounded to the same power strip as the receiver, sub, tv, and all.

Then I take the HTPC and plug it in. As soon as I plug the HDMI cable from the HTPC to the reciever the hum starts. I have tried plugging the HTPC into the same power strip, and a separate power strip.

I know its coming from the HTPC and the only way to connect the HTPC to the receiver is through the HDMI port so I can get video.

You may want to ask in one of the other sections too, like the Receiver/amps/separates and subwoofer forums. There are a bunch of posts like this there and they may be able to help.

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post #11 of 16 Old 02-17-2013, 03:27 PM
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It could be from your HTPC power supply.... but I don't know how you could verify it without replacement.
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post #12 of 16 Old 02-17-2013, 03:56 PM
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I've had the same problem. I'm not saying this device would work for you but it did for me and that device was a "HumX". A black box thingy pluged into the ac outlet then plugging your sub ac cord into it.. That hum once, also came down to the coax cable for the cable tv feed into my htpc tv tuner card. But that HumX took care of the problem
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post #13 of 16 Old 02-18-2013, 01:27 AM
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You stated "The pc is connected to the receiver through the video card using a DVI/ HDMI adapter with an HDMI cable." Does your motherboard have a DVI or HDMI port that you could try & see what happens? Or maybe try a different inexpensive video card with an HDMI port.
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post #14 of 16 Old 02-18-2013, 08:24 AM - Thread Starter
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My video card only has 2 DVI ports. And my Receiver only has HDMI ports. So I do not know how other to connect them.

I will try to see if I have another card laying around, I will try my gaming computers video card but it doesn't have HDMI either it only has display ports which I will test using.

And I hope your on the right track since have been thinking that it is possibly the DVI/HDMI adaptor breaking the ground connection and causing the issue. Either that or the HTPC has so much electrical noise its just pushing it out through the HDMI.
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post #15 of 16 Old 02-18-2013, 08:26 AM - Thread Starter
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I currently do not have the Coax running to the HTPC for testing purposes. It is only run the the cable box. And I have verified that the hum is not coming from the cable coax.
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post #16 of 16 Old 03-01-2013, 07:17 PM
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Quote:
Originally Posted by Psyotik View Post

I currently do not have the Coax running to the HTPC for testing purposes. It is only run the the cable box. And I have verified that the hum is not coming from the cable coax.

It really isn't clear how well you followed my instructions. Disconnect EVERYTHING and add one at a time until the hum comes back. Then disconnect everything again and add just that one thing that made the hum come back the first time through to verify if it really was that last component or if it was really a combination of components.

The one thing you can not count on is to say that everything is hooked up and then you added one more thing and the hum showed up so that means that last thing is the source of the hum. Ground loop hum does not work like that.

The only way to figure out the source of the hum is to reduce your set up to the ABSOLUTE BARE minimum required to create the hum. Any sort of half-assing it will get you half-assed results.

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