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HDMI - Ground noise in amp "Solved" via ground lift at amp, need advice

post #1 of 11
10/12/12 at 6:56am
Thread Starter 
I have a system with a few components in it, but to simplify, with everything disconnected except for computer, receiver (marantz), TV and amp, I get noise in the audio chain. The noise becomes more pronounced as the gpu starts pulling more power for playing games etc.

The connection from computer to receiver is hdmi. RCA from receiver to amp. All components, except for TV, are plugged into the same power strip.

If I put in a cheater at the amp, all noise goes away. Disconnect the computer HDMI and the sound goes away. So it is definitely between those two. If I plug in the hdmi to the comptuer then just touch the other end of the metal tip to the hdmi cable to my receiver, bingo, noise is back.

Pressing mute on the receiver and no change. Change inputs on the receiver, no change. Disconnect TV and no change (so it isn't part of the loop it seems).

So the question now is, what should I do? Just leave the cheater or is there another solution to hdmi allowing ground loops? No balanced outs on the marantz.
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post #2 of 11
10/12/12 at 9:44am
Could it be a bad HDMI cable? I once had a problem when I turned off the AVR the subwoofer would stay on & output & very low level hum. The sub should have turned off because there was no audio signal. But the cheap coax cable feeding the sub was picking up hum from the power cord & keeping it on & of course outputting the hum. Replacing the coax with a better one solved the problem.
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post #3 of 11
10/12/12 at 10:12am
What is a "cheater"? What is the HTPC volume level set at? Can you use audio out from computer to audio in on the receiver?
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post #4 of 11
10/12/12 at 11:10am
a cheater is one of those little grey ac adapters that has the ground prong removed.
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post #5 of 11
10/13/12 at 7:04am
Thread Starter 
Mike: No, All I have to do is take a wire from anywhere on the chassis of the computer over to the receiver. I've also tried different HDMI cables with and without ferrules on the ends, they didn't help.

It is also definitely not an induction issue, I've moved everything around so no cables are next to each other and only cross at 90 degree angles. Still no luck, happens as soon as ground is connected between computer and the rest of the system and can only really be a ground loop.
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post #6 of 11
10/13/12 at 10:57pm
Make sure that all ground/mount screws on the motherboard are properly secured.
Make sure the mount screws for the PSU are snug and secured.
Test a different power strip.
Test a different PSU if possible.

Does the receiver have built in amps? And if so, do you still get the noise by connecting the speaker directly to the receiver? If not, you need a ground loop isolator between the receiver and amp.
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post #7 of 11
10/14/12 at 6:33am
Thread Starter 
Quote:
Originally Posted by vladd View Post

Make sure that all ground/mount screws on the motherboard are properly secured.
Make sure the mount screws for the PSU are snug and secured.
Test a different power strip.
Test a different PSU if possible.
Does the receiver have built in amps? And if so, do you still get the noise by connecting the speaker directly to the receiver? If not, you need a ground loop isolator between the receiver and amp.

Done, done and done.

Receiver has amps, and they also produce noise BUT only if the external amp is plugged in. Unfortunately I have bigger magnepan speakers, no chance for the built in amp running them so the external amp is a requirement. I guess a ground loop isolater is really the way to go, but my understanding is that they can affect the sound output. Is that accurate or not really an issue?
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post #8 of 11
10/14/12 at 6:29pm
Quote:
Originally Posted by Scot Kight View Post

So the question now is, what should I do? Just leave the cheater or is there another solution to hdmi allowing ground loops?
Unfortunately, there's no galvanic isolators for HDMI.

If the cheater works on the amp, that suggests it would also work elsewhere (on the other component that ties to the mains ground that is creating the loop). That's probably the computer, either its 3-prong power cord or something else connected to it.

If the cheater works equally well on the PC's power cord, one option might be to connect it to an isolation transformer such as from Tripp Lite.

The cheater could be left on the amp -- it will not hurt sound quality. It only hurts safety if there is a mains short inside the amp, as the chassis path to ground is no longer the third prong, but the RCA cables, AVR, HDMI cable, PC power cord.
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post #9 of 11
10/14/12 at 9:54pm
Quote:
Originally Posted by Scot Kight View Post

Done, done and done.
Receiver has amps, and they also produce noise BUT only if the external amp is plugged in.
This suggests that the amp is the device at a different electrical potential. You can try connecting a chassis ground directly between the amp and the receiver and then using the cheater on either one of them. This will give a single-point ground and should eliminate the signal. If not, add a chassis ground connection to the PC and use another cheater. Whichever device you do not connect with a cheater should be the home run for all the other chassis grounds. IE: If the PC and receiver have cheaters, they should both be connected directly to the amp. They should not be connected PC->receiver->amp.
Quote:
I guess a ground loop isolater is really the way to go, but my understanding is that they can affect the sound output. Is that accurate or not really an issue?
I've heard that but not seen real evidence of it. My thoughts have always been that if it's the only thing that eliminates your hum, their effect on sound output is definitely less than the hum and therefore acceptable.
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post #10 of 11
10/15/12 at 2:28am
Quote:
Originally Posted by vladd View Post

This suggests that the amp is the device at a different electrical potential. You can try connecting a chassis ground directly between the amp and the receiver and then using the cheater on either one of them.
In my understanding, Marantz receivers do not use a grounded AC cord, so it appears the amp is fighting with the PC.
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post #11 of 11
11/11/12 at 7:30am
I have this same problem. My infinite baffle subs make all sorts of pops and hum sounds but then as soon as I remove the HDMI from the computer to the Denon amp all the problems go away. Did you ever come up with a solution? Ground the receiver maybe? I always heard that was a bad option.
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