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HDMI Ground Loop


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For about 2 years I've had a hum that I just knew was ground loop related.

The hum only existed in the Cinema part of my system.

 

For context:

 

Front of Room

  • Mono Amplifiers connected to dedicated power circuit

Middle of Room

  • All 2-channel related electronics - tapped off dedicated power circuit above.

Back of Room

  • AV related electronics. Preouts from AVR (single ended) run through all to middle of room for HT bypass
  • This is a seperate power circuit to the front and middle of room.
  • Projector connected to this power circuit.
  • Projector connected to AVR on same circuit via HDMI.

 

I hope I have outlined the above clearly enough to make sense without diagrams.

I've been trying to find the cause of the hum for months now, with extension leads joining circuits together etc, isolating individual components and so on.

 

Last night I found the culprit. It's the projector, or moreso the HDMI cable connecting the PJ to the AVR.

If I power down the PJ, the hum completely disappears.

 

I guess my question is, is it surprising that the PJ on a different power circuit to the 2-channel electronics and mono's would cause a ground loop?

And secondly, that the HDMI cable could carry this hum through?

 

Obviously, the most obvious solution is to have the back of room power circuit rewired to the front and dedicated circuit. The reason it wasn't is we used to have bar fridge at the back of the room and I didn't want that on my 2-channel power circuit. We no longer have that so not a problem now.

 

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Yeah that's one thought I had. I haven't investigated if they're 4K friendly though.

The Fibre ones still have a copper connection as well, so I suspect that would not break the loop.

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18 minutes ago, Marc said:

Yeah that's one thought I had. I haven't investigated if they're 4K friendly though.

The Fibre ones still have a copper connection as well, so I suspect that would not break the loop.

Do you run a 12v trigger to the projector for a drop down screen.

 

youve changed projectors to so couldn’t relate to particular projector either and more circuit related. I know you changed avrs did it start with that ? Or go through with that update as well ?

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No trigger problem - as it's a wireless sender/receiver so no physical connection.

Yeah, the problem has carried through with component upgrades.

 

I guess I have already established the prob/cause, but just surprised that HDMI could carry the hum of the ground loop through more than anything I suppose.

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1 hour ago, Marc said:

If I power down the PJ, the hum completely disappears.

What about if you leave the projector on, and disconnect the HDMI cable from it?

 

Where does the hum come from?   Your speakers?   All the speakers?

 

1 hour ago, Marc said:

Obviously, the most obvious solution is to have the back of room power circuit rewired to the front and dedicated circuit.

Does that solve the problem?   Why do you think so?   (At this stage, I don't see enough info to know it would)

 

If you power everything at the back of the room from the circuit at the front?   (Try it - grab a cheap extension cord and power boards, and fire it up) 

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Being one-handed still prevents me from trying as you suggest just yet (need a ladder to get to power point of PJ) and don't feel like any more surgery just yet :)

Will report back as I delve deeper though. Thanks for the logical approach.

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8 hours ago, Marc said:

Back of Room

  • AV related electronics. Preouts from AVR (single ended) run through all to middle of room for HT bypass
  • This is a seperate power circuit to the front and middle of room.
  • Projector connected to this power circuit.
  • Projector connected to AVR on same circuit via HDMI.

Not as intuitive as changing the power supply Marc  but anecdotally the eradication of ground loops is helped greatly by balanced xlr compared to unbalanced rca's . Have you had that option in the recent '"pervasive hum " past or strictly running unbalanced ? Needless to say not a cheap experiment though switching to the other ;)

You didn't specify any coax from pvrs apple tv's etc etc so an inline filter is another possibility .

https://www.audioholics.com/home-theater-connection/ground-loops-eliminating-system-hum-and-buzz

 

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