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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => Pro AV Forum => Topic started by: Corne Stapelberg on February 14, 2011, 08:27:10 AM
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Is there a VGA HUM ELIMINATOR on the market?
What do you use to eliminate hum assosiated with VGA images?
Regards
Corne'
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The best solution is to find and address the cause of the hum. Otherwise:
http://www.extron.com/product/product.aspx?id=gli2000&subtype=45&s=4 (http://www.extron.com/product/product.aspx?id=gli2000&subtype=45&s=4)
http://www.jensen-transformers.com/datashts/vbh5bb.pdf (http://www.jensen-transformers.com/datashts/vbh5bb.pdf)
You may have to use HD15 to 5 BNC breakouts if you're not already running five wire cable.
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The Extron units seem to work pretty well, though they dont always completely fix the problem. Usually helps when all the video devices are coming off of one power source.
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Is the hum visible on all displays or just the projectors?
Hum bars are a visual display of a ground loop.
The most common one is between control and the projectors. Also from cameras to control.
Disconnect all the power cables from the projectors/cameras and add them one at a time until you see which one(s) are causing the problem.
You can use an AC plug ground pin lift to test and see if the problem goes away.
Also, make sure when you are mounting projectors to a truss that you use some gaff tape to isolate the clamp from the metal truss.
Sometimes an audio connection from a mixer to video control can be the problem. Use isolation transformers on audio feeds.
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Is there a VGA HUM ELIMINATOR on the market?
What do you use to eliminate hum assosiated with VGA images?
Regards
Corne'
I believe you are talking about hum that occurs when you have a computer with a stereo plug out into your sound console and a VGA cable also connected to the same computer. You probably noticed that when you disconnect the VGA, the hum goes away, so you isolated it to the VGA. This is the exact scenario I had a couple of years ago. Our solution: We took a stereo plug to 1/4" and ran it into a DI box (Whirlwind IMP 2) and then ran the XLR from the DI box to the sound console. Use the ground lift on the DI Box and the hum is eliminated.
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If you're in a situation where the projector(s) are far from the source video and you cannot feasibly get power to the projectors on the same circuits or sub panels as the video source, you might consider VGA to fibre optic converters. These will inherently eliminate any ground loops issues as well as give you extremely long video 'wire' run capability.
Greg
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Is there a VGA HUM ELIMINATOR on the market?
What do you use to eliminate hum assosiated with VGA images?
Regards
Corne'
I experienced this on an LCD projector from a computer in one of my student computer labs.
This is simply "seeing" the ground loop in the video. I simply use a ground lift on the projector
and the issued was resovled.
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I experienced this on an LCD projector from a computer in one of my student computer labs.
This is simply "seeing" the ground loop in the video. I simply use a ground lift on the projector
and the issued was resovled.
So you removed a safety ground from a piece of gear designed with a safety ground?
Really quite a bad idea (if thats what you meant). You should instead isolate the video signal link.
Lee
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I experienced this on an LCD projector from a computer in one of my student computer labs.
This is simply "seeing" the ground loop in the video. I simply use a ground lift on the projector
and the issued was resovled.
As Lee noted, what do you mean by this? If you mean that you used a device to lift the signal ground then I am curious as to what exactly you used. If you mean that you used an adapter intended to provide a safety ground path by connecting the ground wire of the three prong device via tab or wire via a metal plate to a metallic conduit system but did not attach the tab or wire to provide that path, then while that may have helped identify the problem it is also unsafe and most likely a code violation, thus it should be removed as soon as possible.
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As Lee noted, what do you mean by this? If you mean that you used a device to lift the signal ground then I am curious as to what exactly you used. If you mean that you used an adapter intended to provide a safety ground path by connecting the ground wire of the three prong device via tab or wire via a metal plate to a metallic conduit system but did not attach the tab or wire to provide that path, then while that may have helped identify the problem it is also unsafe and most likely a code violation, thus it should be removed as soon as possible.
I pulled about 20 of these from an install. Every single piece of gear had one on it. Including the home depot power strips. Once I moved all of the audio gear onto the transformer, they were surprised at how quiet it was without the ground lifts.
If this is what you are talking about, please don't use these permanently. As I think Brad is pointing out.
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If this is what you are talking about, please don't use these permanently. As I think Brad is pointing out.
Yes. There was a time when electrical systems had only hot and neutral conductors and relied on metallic plates, boxes and conduit to serve as the safety ground path and the purpose of those adapters is to use the tab or wire on them to adapt modern three wire devices with a dedicated safety ground conductor to those older power distribution systems, the exact opposite of being used to disrupt or break that path.
Devices with two prong plugs are 'double insulated' and designed to isolate the chassis and external surfaces from becoming 'hot'. However, devices with three prong plugs rely on the safety ground path to address conditions such as an internal short and if that path does not exist then the current has no where to go until something like someone touching the device becomes the safety ground path. That is why with the potential exception of GFCI circuits under certain conditions, not having a dedicated safety ground path is a NEC violation.
Another common fix for ground loops are 'hum eliminator' devices that go between the device being powered and the receptacle. These typically electrically isolate the safety ground path between the device and the receptacle until conditions indicate it is needed, at which point current is allowed to flow through that path. The problem with these devices is that if the current and voltage involved are large enough then the device can potentially fail in a manner that provides no safety ground path. That is why you probably will not find any such devices that are UL listed.
As it may be the source of much confusion, it should be clarified that lifting the ground of an audio or video signal path, which is what the "ground lift" switch on many audio devices does and which is in many cases a quite acceptable practice, is quite different than lifting the ground of the electrical system.
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As already stated, I agree the adaptor is made to "pick Up" a ground source by using the cover plate screw attached to the brass tab sticking out from the adaptor.
While the tab will help hold the adaptor to the receptacle in place (If you use the screw) thats not why its there.
The adaptors, used properly will enable you to pick-up a ground (If a path Exits) from a two prong receptacle. (Older Systems)
The device is not a ground lift device (although many call it that and improperly use it for that)
Lifting a Ground is a Trouble Shooting Aid only, Not a solution to a grounding problem.
Regards, John