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Earth Loop - HDMI


BobJ
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We are projecting animations onto the cyc. The MP4's have audio we want to pipe to the desk. When I plug the laptop output sound into the board the sound is great. But as soon as I plug the HDMI cable in we get a horrendous earth loop hum! I checked the projector and sound board power cables are grounded properly though one is FOH and the back stage. I removed the laptop charger but his made no difference. Ideas' suggestions welcome. I have to go in tomorrow early to fix this and not sure where to start.
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We are projecting animations onto the cyc. The MP4's have audio we want to pipe to the desk. When I plug the laptop output sound into the board the sound is great. But as soon as I plug the HDMI cable in we get a horrendous earth loop hum! I checked the projector and sound board power cables are grounded properly though one is FOH and the back stage. I removed the laptop charger but his made no difference. Ideas' suggestions welcome. I have to go in tomorrow early to fix this and not sure where to start.

I ALWAYS use an isolating transformer to feed a laptop audio into anything else. They are notorious for this problem and I've also experienced sound card damage due to the power supply not being at ground potential.Something like this is perfect:https:

 

https://cpc.farnell.com/pulse/pls00550/ground-loop-isolator-3-5mm-to/dp/AV25544?st=3.5mm%20to%20usb-2%20b

 

It will remove any doubts about ground loops and protect your equipment. In my case it has been multiple strangers laptops per year and they regularly comment about the lack of hum etc.

Edited by sunray
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We had this exact same problem a few years ago. The projector was powered from the shows distro on stage, while the sound desk and QLab Mac were powered from a different supply at front of house. This is usually fine, especially with the use of Cat5/6 in place of traditional analogue multicores. However as soon as the HDMI lead from the projector was plugged in to the laptop there was buzz from the sound system. In the end we solved the problem by running an extra power cable from their distro to the front of house mix position, thus eliminating the ground loop, and the buzz.
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We had this exact same problem a few years ago. The projector was powered from the shows distro on stage, while the sound desk and QLab Mac were powered from a different supply at front of house. This is usually fine, especially with the use of Cat5/6 in place of traditional analogue multicores. However as soon as the HDMI lead from the projector was plugged in to the laptop there was buzz from the sound system. In the end we solved the problem by running an extra power cable from their distro to the front of house mix position, thus eliminating the ground loop, and the buzz.

 

 

What they said.

Run all the kit from the same power source if you can. Then they all have the same earth.

 

 

 

 

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What they said.

Run all the kit from the same power source if you can. Then they all have the same earth.

 

Using DI boxes for the audio as suggested above is the better solution. Running out long power cables sometimes doesn't work and is often a pain to do.

 

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What they said.

Run all the kit from the same power source if you can. Then they all have the same earth.

 

Using DI boxes for the audio as suggested above is the better solution. Running out long power cables sometimes doesn't work and is often a pain to do.

 

Or better yet, avoid the generally noisy headphone amp with a transformer isolated USB audio interface. https://www.amazon.co.uk/Peavey-3001370-USB-P-USB-Playback/dp/B004A4PSEU

 

Mac

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The peavey USB-Ps are great (we have to order them from BHP with international shipping as they don’t sell them here) or ground loop isolator from Kenable should fix the problem.

https://www.kenable.co.uk/en/audio-/audio-connectors/audio-adapters/8073-35mm-stereo-ground-loop-isolator-female-to-male-earthing-for-audio-008073-5015972172537.html

 

We had the same problem except in our case the VGA went noisy and the screen started wobbling as well.

Edited by TomHoward
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Or better yet, avoid the generally noisy headphone amp with a transformer isolated USB audio interface. https://www.amazon.co.uk/Peavey-3001370-USB-P-USB-Playback/dp/B004A4PSEU

 

And if you are in the UK...

 

https://www.interspaceind.com/shop-our-products/product/50-usb-balbox-2/category_pathway-44.html

 

post-207-0-58833700-1634737085_thumb.jpg

 

The link I provided was for Amazon UK, do they not ship to the UK?

 

Mac

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We are projecting animations onto the cyc. The MP4's have audio we want to pipe to the desk. When I plug the laptop output sound into the board the sound is great. But as soon as I plug the HDMI cable in we get a horrendous earth loop hum! I checked the projector and sound board power cables are grounded properly though one is FOH and the back stage. I removed the laptop charger but his made no difference. Ideas' suggestions welcome. I have to go in tomorrow early to fix this and not sure where to start.

So to recap:

 

1)you are perfectly happy with the sound without the HDMI plugged in.

 

2) you are perfectly happy with the picture quality.

 

I've experienced this exact situations on a number of occasions and to date something of this ilk: https://cpc.farnell.com/pulse/pls00550/ground-loop-isolator-3-5mm-to/dp/AV25544?st=3.5mm%20to%20usb-2%20b ,for £7 plus delivery has corrected it every time.

 

 

Additionally a fixed installation in a venue suffered for several years, when we did the AV for a presentation I added isolation transformers which improved both sound and VGA video to projector. Their caretaker couldn't believe it as the installers had failed to sort the problem by fitting a Kramer unit.

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A tempt test showed it was GL caused by the two power outlets being a long way apart. We have a PYLE Mini Hum Eliminator - GL Isolator coming tomorrow. Thanks for the ideas and comments.
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A tempt test showed it was GL caused by the two power outlets being a long way apart. We have a PYLE Mini Hum Eliminator - GL Isolator coming tomorrow. Thanks for the ideas and comments.

I don't know the product but the write up on B&H website looks to be just the job. (That is apart from the 11:1 transformer ratio typo rolleyes.gif)
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Hmmm… That didn’t last long. When I posted the link they were available and listed as £69. The alternative posted looks good, using a usb audio output device not only provides transformer isolation, but generally provides significantly better audio quality.

 

Mac

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