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tnargs 2nd May 2012 03:34 AM

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.


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)?

abraxalito 2nd May 2012 04:07 AM

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!

marce 2nd May 2012 06:09 AM

Not a good idea.
You need to do a schematic of your full system and work out all the interconnections, including mains cables first.

tnargs 2nd May 2012 06:43 AM

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?

dangus 2nd May 2012 07:12 AM

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.

SoNic_real_one 2nd May 2012 10:43 AM


Originally Posted by tnargs (
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:

tnargs 2nd May 2012 12:52 PM

Thanks SoNic. I must say the botton diagram is pretty much what I have now. Except with multiple HDMI sources added.

tnargs 2nd May 2012 12:57 PM

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

bigtexas 8th April 2013 12:45 PM

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?

tvrgeek 29th August 2013 10:47 AM

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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