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Ground Loop Hum coming from HTPC - Page 2

post #11 of 19
Quote:
It is a ground loop Caused by the PC and the Subwoofer

Explain to me how I am incorrect. The ground loop is caused by the cabling between the receiver and the subwoofer. A coaxial cable which is analog.

BTW, I design audio/video systems for a living. I know what causes ground loops and it isn't digital cables. Get a properly terminated coaxial cable connected to the sub and the problem should go away. I would use quad shield RG6.
post #12 of 19
Question. Do you hear a buzz or a hum? Thanks.
post #13 of 19
A lot of good information in this link for you.

http://forum.blu-ray.com/showthread.php?t=97963

Note:

GROUND HUM

Generally, a ground loop is formed when an electrical system has more than one path to the electrical ground. The path between these points form a loop that works like an antenna and picks up noise. Grounding problems are normally found because you are using 2 prong and 3 prong power cords and plugging them into different wall sources.

You need to find the source of the problem. The only way is to unplug them one by one to see what is causing the hum.

Usually, the most common sources are cable TV boxes and computers that are connected to an A/V receiver. Unplug the cable box and/or the computer and see if it improves the hum.

Sometimes, changing the wall outlets solves the problem.

Don’t run interconnect and speaker cables parallel to power and extension cords.

Don’t coil up the excess length of a cable. If you have excess cables, instead of coiling them, you should make a figure 8 with them.

Use an RG6 digital coaxial subwoofer cable and move it away from the other cables. This may help.

Buy a good power conditioner/surge protector and plug all your equipment into that one, including the subwoofer amp. Make sure the coax cables for the cable TV also go through the conditioner. This may solve your noise problem.

Buy a ground loop isolator.
post #14 of 19
Thread Starter 
I have determined it is the pc causing the loop.

I have all devices plugged into the same power conditioner already.

I will order a ground loop isolator and hope it does not muddy up the sub
post #15 of 19
Quote:
Originally Posted by VABuckeye View Post

Explain to me how I am incorrect. The ground loop is caused by the cabling between the receiver and the subwoofer. A coaxial cable which is analog.

BTW, I design audio/video systems for a living. I know what causes ground loops and it isn't digital cables. Get a properly terminated coaxial cable connected to the sub and the problem should go away. I would use quad shield RG6.
^^^This^^^Some good info thanx!
I used to run into this with car audio all the time. A higher quality rca (composite?) cable almost always fixed the issue. Ground loop isolator only made sound quieter. I'd get a new cable, something with better shielding.
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post #16 of 19
Thread Starter 
You were only wrong because you didn't full read my original post. I have disconnected everything. I dont have any speakers connected or anything. No cables are being crossed the entire entertainment center has been disassembled and is spread out in my living room for testing.

No other cables are involved.
post #17 of 19
While I certainly agree that no hum can be introduced over the digital transport between the pc and amp, the amp still has to produce an analogue signal to drive the speakers and this can be affected by a ground loop between the two devices.

The metal shroud of the hdmi plugs are connected to each other via the (usually) braided shield of the hdmi cable. The socket shrouds are connected to the pc chassis and the amplifier chassis. The pc chassis is earthed and the av chassis is not. If the av amp chassis floats to a voltage it will induce a current along the hdmi cable shield to ground through the pc power supply or via the coaxial cable shield to ground via the sub surely?

If I'm wrong, I'd be very interested to hear the reason why as it makes sense to me! While not privy to the ins and outs of audio equipment design, amongst other things, I've designed interconnect cables between high power (4 kW) servo motors and their drives so have had to mix high voltage, high current and low voltage, weak analogue signals for the feedback resolvers. Ground loops here could kill you and poor noise immunity could render the system useless so I made sure I did my homework first!

I think breaking the shield of the hdmi cable at the receiver end would fix your problem but I'm happy to be shown to be wrong if that's the case
 
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post #18 of 19
Thread Starter 
And this issue has been resolved. The pc was causing the ground loop. The case that it is in is has a painted interior. So when I remounted the mother board I made sure to remove paint in each of the motherboard mounts. So with the motherboard gound to the HTPC properly the issue is resolved.

So the PC was causing the ground loop and was transfering it to the sub through the HDMI cable.

Pharcycle you are correct I attempted to remove the shielding from the HDMI cable and it did resolve the hum as well. Thats when I decided to tear apart the PC to find out what inside the PC was causing the issue.
post #19 of 19
ahh, yeah, painted interior could do it!

Also, if not too late, I'd recommend removing paint around the expansion slots (screws and mounting faces) as I think a lot of cards would expect the bracket to be earthed too.

glad you got rid of the hum
 
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