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Author Topic: You remove ground loop roll with a 3 prong to 2 prong adaptor what next...  (Read 6789 times)

Nicholas Bailey

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We have a ground loop roll on the projectors at our church and LCD in the lobby.  It disappears with adding the death ground lift adaptor on the computer.  Whats the next step to make it safe?

Three of the projectors are in the worship center.  I can see that the 4 square box the outlet that powers two of them are mounted on the red iron.  The other projector is in the sound booth.   There is also a projector and LCD in another room.

I really do not want to leave the ground adaptor in place.

I look forward to you replys.

Nick
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Mike Sokol

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We have a ground loop roll on the projectors at our church and LCD in the lobby.  It disappears with adding the death ground lift adaptor on the computer.  Whats the next step to make it safe?

Three of the projectors are in the worship center.  I can see that the 4 square box the outlet that powers two of them are mounted on the red iron.  The other projector is in the sound booth.   There is also a projector and LCD in another room.

I really do not want to leave the ground adaptor in place.

I look forward to you replys.

Nick

Rather than lifting the ground on the sound system, you should consider eliminating the ground loop current coming from the projectors. We typically run CAT-5 or CAT-6 with Baluns (Bal-Unbal transformer) adapters for long projector runs plugged into different outlets. CAT-5 is good for 1080P HD, while CAT-6 is called for to send 4K video.

This follows my general grounding mantra of "ground locally / isolate remotely". Each piece of AV gear should get its safety ground from the local EGC conductor in its local power outlet, and then you should isolate the shields interconnecting the gear. I have one church site where we installed a 1-in/4-out active HDMI DA (Distribution Amp) with four baluns feeding video screens and projectors in three different rooms. Not a hum bar to be seen or hum to be heard once we got that in place.
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Mike Sokol
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Frank DeWitt

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We have a ground loop roll on the projectors at our church and LCD in the lobby.  It disappears with adding the death ground lift adaptor on the computer.  Whats the next step to make it safe?

Three of the projectors are in the worship center.  I can see that the 4 square box the outlet that powers two of them are mounted on the red iron.  The other projector is in the sound booth.   There is also a projector and LCD in another room.

I really do not want to leave the ground adapter in place.

I look forward to you replys.

Nick

Mike answered your question, I just want to jump in and hold up your post as the template all should follow.  You identified the problem. You described how you proved that is the problem, and then asked how to fix it in a safe way.  Good solid post.
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Keith Broughton

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Rather than lifting the ground on the sound system,
He lifted the ground from the computer, not the sound system.

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John Rutirasiri

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We have a ground loop roll on the projectors at our church and LCD in the lobby.  It disappears with adding the death ground lift adaptor on the computer.  Whats the next step to make it safe?

Three of the projectors are in the worship center.  I can see that the 4 square box the outlet that powers two of them are mounted on the red iron.  The other projector is in the sound booth.   There is also a projector and LCD in another room.

I really do not want to leave the ground adaptor in place.

I look forward to you replys.

Nick

Are you using VGA or HDMI?
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Mike Sokol

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Are you using VGA or HDMI?

I've been at a few churches that still have composite video running on BNC/coax, and that seems to be with worst for ground loop hum bars. They also make video isolation transformers that will lift that kind of ground loop.
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Mike Sokol
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Nicholas Bailey

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They have VGA cable pulled to all the projectors and the one LCD.

I agree with you Mike if I were to do the install today I would use a cat6 solution.

Any other sugggestions without changing the cabling?


Nick


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Jonathan Johnson

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They have VGA cable pulled to all the projectors and the one LCD.

I agree with you Mike if I were to do the install today I would use a cat6 solution.

Any other sugggestions without changing the cabling?

A quick Google search for "vga isolation transformer" returned this as the top result, so they are out there:

http://www.allenavionics.com/VHumElim/VI-VGA.htm
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Lee Buckalew

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A quick Google search for "vga isolation transformer" returned this as the top result, so they are out there:

http://www.allenavionics.com/VHumElim/VI-VGA.htm

Extron also has one as does Jensen transformers.  These would be RGBHV, 5 wire video isolation transformers that are going to have a significant cost.  Probably somewhere between about $500.00 and $1000.00 per computer output. 
The Jensen is linked here http://www.jensen-transformers.com/product/vbh-5bb/
They are $735.00 ea. at Broadcast Supply.  The Jensen is lower cost than the Extron and I would choose Jensen over Extron.  The Allen Avionics HEC-5000 referenced by Jonathan is $616.25 from the same supplier.
You will want to look at the cost of pulling new cable and purchasing the appropriate converters to utilize the twisted pair options that are out there vs. simply adding the isolation transformers.

Lee
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Keith Broughton

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While I agree that the perfect solution is a VGA iso, I'm still not clear on what running a laptop (if it is a laptop) with no AC ground is an issue.
I have seen plenty of laptops that don't have 3 pin AC plugs.
My all metal Macbook has no ground but my all plastic Lenovo does have a ground. Makes me wonder.
BTW... have the same issue at a local gig and we use an SDI to VGA converter which seems to do the trick.
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