Grounding and HDMI - any suggestions - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 2 Old 03-24-2013, 06:09 PM - Thread Starter
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The Problem - a 60HZ hum audible in the subwoofer only and only when playing from an HDMI source.

I have been experiencing a hum in my subwoofer system - 60Hz roughly - I can't measure exactly - and it's existed for quite a while and I didn't really pay much attention because blu-ray 5.1 sources typically drowned it out watching movies - you'd only notice it in very quiet passages. I thought it was bad caps or something in my 11 year-old Pioneer A/V 5.1 Receiver. It was most annoying when playing streamed internet programming - my wife didn't even notice it.

So I recently saw a good sale on a Yamaha receiver that had 4 HDMI inputs which nicely lined up with my needs. On the Pioneer I had no HDMI inputs - only standard composite cabling or S-Video and optical and coa for audio. So in the Pioneer I ran optical/coax outputs for audio from my HD sources to the Pioneer and ran the HDMI or component video cables to the TV, a Samsung DLP. I was always curious about the hum because I thought optical would isolate any grounding issue.

When I got the Yamaha hooked up I was surprised to see I still had the same hum. But not when playing from the build in FM receiver - only from HDMI sources would I get the hum. So I took an MP3 player to the subwoofers and played them from an mp3 player and assured myself it wasn't the subwoofer amps. The I ran grounds between all the HDMI devices - 2 blu-ray and an upconverting DVD recorder and a PC thru a DVI -to HDMI converter - still had hum.

Then researched this forum and saw where someone had a problem with hum on a DVI connection and that the solution was to interrupt the ground to his overhead projector. So that inspired me to test to see if my DLP TV was causing the hum. All the devices including the TV get their power from a MONSTER power strip so it was hard to believe the TV was causing the problem - but I ran tests with the TV on, the subwoofers on, and the receiver off - and as soon as I turned on the TV the subwoofers began humming. So I put a 2-prong adapter on the 3-prong TV plug and tried again - no hum!!

This Samsung model DLP I have uses an LED lightsource as opposed to a projector bulb. So for the moment I'm not too worried about not grounding the TV AC - and the TV is not connected to an external antenna or cable system or anything else that goes outside. In addition I live in an area of underground utilities.

So to my question - What risk am I accepting by powering the TV without an AC ground? The TV is connected to the receiver and 4 other devices all off the same powerstrip. The receiver and the other devices are all grounded to each other through a ground I added. So I want to know if I should pursue other grounding arrangements like running coax from the Monster strip to the TV and the receiver and see what that does to the hum? I was going to try that today but I have to move a lot of furniture to get back behind the set and now that it's late in the day I'm going to have to wait until next weekend to get behind there. The problem is solved for the moment but I would like to know the nature of the risk I'm taking by ungrounding the TV power plug.
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post #2 of 2 Old 03-24-2013, 08:08 PM
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This really isn't a HDMI issue. It is a ground loop problem. Lifting the ground at the TV broke the ground loop. You can find everything you need to know in one of the threads on ground loops.
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