HDMI - Ground noise in amp "Solved" via ground lift at amp, need advice - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 16 Old 10-12-2012, 06:56 AM - Thread Starter
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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 16 Old 10-12-2012, 09:44 AM
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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 16 Old 10-12-2012, 10:12 AM
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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 16 Old 10-12-2012, 11:10 AM
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a cheater is one of those little grey ac adapters that has the ground prong removed.
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post #5 of 16 Old 10-13-2012, 07:04 AM - Thread Starter
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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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"Don't touch that, this isn't your house and that isn't your tv!" she says.

"But look at it, the contrast is completely blown out, the color is all off and that tint. This will only take a sec..."
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post #6 of 16 Old 10-13-2012, 10:57 PM
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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 16 Old 10-14-2012, 06:33 AM - Thread Starter
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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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"Don't touch that, this isn't your house and that isn't your tv!" she says.

"But look at it, the contrast is completely blown out, the color is all off and that tint. This will only take a sec..."
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post #8 of 16 Old 10-14-2012, 06:29 PM
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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 16 Old 10-14-2012, 09:54 PM
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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.
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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 16 Old 10-15-2012, 02:28 AM
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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 16 Old 11-11-2012, 07:30 AM
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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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post #12 of 16 Old 06-27-2016, 03:34 AM
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I am having this exact problem. I see this thread is marked solved, I would LOVE to know what the solution was?

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post #13 of 16 Old 06-27-2016, 03:48 AM
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Originally Posted by Javs View Post
I am having this exact problem. I see this thread is marked solved, I would LOVE to know what the solution was?
looks like the OP used a cheater plug which lifts the AC ground

the most common cause of such noise is the cable TV feed: it is usually at a different ground potential than your house ground, hence the hum: if you have cable TV service, try disconnecting the cable feed: if this fixes the issue install a ground loop isolator (cheap Radio Shack part or your cable company may give you one)

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post #14 of 16 Old 06-27-2016, 06:16 AM
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Quote:
Originally Posted by markrubin View Post
looks like the OP used a cheater plug which lifts the AC ground

the most common cause of such noise is the cable TV feed: it is usually at a different ground potential than your house ground, hence the hum: if you have cable TV service, try disconnecting the cable feed: if this fixes the issue install a ground loop isolator (cheap Radio Shack part or your cable company may give you one)
Hmm, I dont have cable television or anything like that. Only HDMI sources. HTPC, and Bluray players.

Here is the odd thing, I disconnected everything and only had the one HDMI going from the PC to the Marantz 7702 and the noise was still there, I even tried outputting from the 7702 to another power amp (I have two), different power lead, different HDMI cable, different HDMI input ports on the Marantz, different ports on the PC (HDMI, DP), and also tried different power sockets including trying the same power board the amps live on... real head scratcher.

It only shows up when the GPU is under load, kind of a fast ticking noise. I also tried my old video card. GTX 1080 right now, GTX 970 before that. Both have the noise. The only thing I havent tried is a new PC powersupply but I highly doubt its that. Its a very good Corsair 1000w PSU. I also tried completely disconnecting everything from the PC, aux audio, keyboards, everything but the HDMI.

Muting the amp makes no difference, changing the amp input away from the HDMI input still retains the sound... very odd. The sound is much louder when there is no Projector display plugged in to the amp, and goes a little quieter when the projector is plugged in. That's odd too.

Kinda sounds like I need to ground my Marantz properly some how, that amp only has a two prong power lead. May explain why some of the noise went away when I plugged in the JVC Projector which has a 3 prong lead.

Odd thing is its ONLY when the computer is under any kind of load... I use MadVR so only really when that is running a film does this noise occur. I could listen to music all day and its perfect, watching movies without MadVR is perfect too...

Running games also produces this noise before you say it could be MadVR....

Any thoughts?

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post #15 of 16 Old 06-27-2016, 06:47 AM
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I've got my preamp/processor plugged into a power conditioner. My HTPC is plugged into a separate UPS with voltage regulation and filtering. The TV is plugged into a TrippLite line conditioner and surge suppressor, as are all of the monoblock power amps and powered subwoofer in my 7.1 surround system. I have no issues with ground hum whatsoever. The line conditioner provides clean regulated power to the audio system and the UPS provided a battery backup and line filtering to the HTPC and will keep it up and running during the frequent momentary brownouts we have here during the summer. None of my power amps have grounded plugs.
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post #16 of 16 Old 06-27-2016, 06:57 AM
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Quote:
Originally Posted by Javs View Post
It only shows up when the GPU is under load, kind of a fast ticking noise. I also tried my old video card. GTX 1080 right now, GTX 970 before that. Both have the noise. The only thing I havent tried is a new PC powersupply but I highly doubt its that. Its a very good Corsair 1000w PSU. I also tried completely disconnecting everything from the PC, aux audio, keyboards, everything but the HDMI.

Muting the amp makes no difference, changing the amp input away from the HDMI input still retains the sound... very odd. The sound is much louder when there is no Projector display plugged in to the amp, and goes a little quieter when the projector is plugged in. That's odd too.
I ran into a similar issue with PC(s) and a Denon AVR-X5200W. However in my case the whine/static was there 100% of the time (off and on). I could even "hear" the hard drives spin up. However the noise showed up only in my twp pre-out channels that were connected to a AudioSource amp (Atmos - rear heights). It was there even when I switched inputs on the receiver as well.

I tried three PCs (varying power supplies) and all three had the issue. However the moment I connected a media player (say a Shield TV) using the same cables it was gone. I never found a solution although I did try a cheater plug and numerous combinations of connecting the equipment to different outlets (including a BrickWall).

Since I have sold the receiver it's a mute issue at this point. I'll see if the new receiver behaves accordingly when it arrives...

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