How to break possible HDMI ground loops - diyAudio
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Old 2nd May 2012, 04:34 AM   #1
tnargs is offline tnargs  Australia
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Default How to break possible HDMI ground loops

Hi, (this is the least-wrong forum I could find on diyaudio )

I have ground loop hum and am busy checking potential loops.

One thing I see is six HDMI cables connected to my AVR (4 sources, 2 displays). Three of these six devices are mains-earthed. Which says to me there are 3 redundant earth loops I would like to isolate.

If these were all analogue RCA connections I would break the signal earth shield lines for these 3 mains-earthed components. But I don't know what to do about them being HDMI.

Questions:

Am I right, can HDMI cables cause earth loops? Or are they isolated from each other and from chassis earth in a mains-earthed component?

Is it advisable to cut the earth wire in an HDMI cable if components at both ends have chassis earths? If so, how (which wire)?
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Old 2nd May 2012, 05:07 AM   #2
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I have a decoder board to hand and just buzzed out the 0V connections on the input and output sockets. There are 5 0V connected pins, not counting the overall shield. Wikipedia has the details : HDMI - Wikipedia, the free encyclopedia

Whereas the main data pairs use LVDS and can tolerate perhaps up to 1V of common mode voltage, there are other single ended channels which may well not.

Sounds like a minefield - good luck!
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Old 2nd May 2012, 07:09 AM   #3
marce is offline marce  United Kingdom
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Not a good idea.
You need to do a schematic of your full system and work out all the interconnections, including mains cables first.
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Old 2nd May 2012, 07:43 AM   #4
tnargs is offline tnargs  Australia
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HDMI pins :worry:

schematic: yes I did that and there are several possible ground loops involving RCA cables and several involving HDMI.

I will fix up the RCA loops first, but I was wondering how to tackle the HDMI side?
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Old 2nd May 2012, 08:12 AM   #5
dangus is offline dangus  Canada
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Probably the best bet is to power everything from a single wall outlet, through a single power bar or line filter.

Connections to cable TV or satellite dishes are likely to be the main offenders when it comes to ground loops, since they have different grounds than the mains power system. Cable TV is easy enough to isolate - use a couple of 75 to 300 ohm transformers back to back in a pinch. Satellite isn't trivial since the receiver supplies power to the LNB and maybe switch or positioner. Perhaps there's a box for that application that has an isolated power supply and appropriate isolation for the RF and low frequency (supply voltage switching to select polarization, Diseqc or whatever signals for other functions) signals.

Ethernet is AFAIK always transformer-coupled and therefore galvanically isolated.
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Old 2nd May 2012, 11:43 AM   #6
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Quote:
Originally Posted by tnargs View Post
Which says to me there are 3 redundant earth loops I would like to isolate.
Actually... no. All your devices have isolating transformers on the mains section. There are no "ground loops" because of that.
I would rather suspect that one of your devices doesn't have a good ground around an analog signal cable. Do you connect anything on analog inputs of the AVR?
Because I saw this: "If these were all analogue RCA connections I would break the signal earth shield lines for these 3 mains-earthed components" - that is the surest way to get noise on your analog.
Correct grounding from here:
Click the image to open in full size.
Click the image to open in full size.

Last edited by SoNic_real_one; 2nd May 2012 at 11:51 AM.
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Old 2nd May 2012, 01:52 PM   #7
tnargs is offline tnargs  Australia
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Thanks SoNic. I must say the botton diagram is pretty much what I have now. Except with multiple HDMI sources added.
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Old 2nd May 2012, 01:57 PM   #8
tnargs is offline tnargs  Australia
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Thanks Dangus. Yes, I am using a single wall outlet / powerbar setup. With one exception: the projector, which plugs into a ceiling powerpoint and runs HDMI to the AVR. So that's a possible problem.

I will also look into the TV aerial setup. cheers
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Old 8th April 2013, 01:45 PM   #9
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Is it true that you get some signal loss over long distances? I found this 20m HDMI cable but Im not sure what the quality will be like. Is it better to use a HDMI extender?
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Old 29th August 2013, 11:47 AM   #10
tvrgeek is offline tvrgeek  United States
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New Outlaw 957 and oppo103. Plug in the HDMI and I get 60 Hz and some noise. Outlaw is 2-pronng, oppo 3. Tried a 2-prong on the oppo. nope.
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