lifing ground on vga connection between projector and computer

[buggyboy]

Hello again,

I've tracked down a ground loop caused by our projector being on a different circuit from the rest of the sound gear.

If this were a problem in an audio cable I know how to fix it... modifing the cable to only connect + and - and lifting the gnd. (between the audio components, not the PE ground).

My question is how to lift the ground on a vga cable.

The other questions I discovered can be posted in other threads.

Thanks again

[waynehoskins]

The short answer is you can't. VGA is an assortment of unbalanced signals, so the common connection is necessary for it to work.

What you need is a set of five video isolation transformers, commonly called humbuckers. They're not cheap, but they're the solution to your problem. Presuming you can't fix the electrical problem. Maybe my case is rare, but at my church I don't have any problems from things being on different circuits. Perhaps we're lucky and have very good grounding.

[Borggren]

You can convert the VGA signal to cat5, and convert back again to VGA. Cat5 cable is unshielded and therefore give you the groundlift you need.
The cat5 to VGA converter should be powered by the same line as your projector.

[buggyboy]

small edit, the singal comes out of a DVI port on the projector computer...goes to an adapter and then to a vga cable run. I'm not sure if the projector end has another adapter or not.

I'm not sure if that makes a difference.

thanks

[waynehoskins]

I don't think the DVI adapter on the computer would be a factor.

Cat5 baluns may be the inexpensive solution you need, also providing the benefit of inexpensive cabling -- somewhat moot since the VGA cable is there already, but you can run a UTP cable alongside it for dirt-cheap.

Of course, if you can get the electricity fixed, the whole thing becomes a non-issue, along with other potential ground-difference gremlins.

[pdc]

Exactly. Why band-aid it?

[buggyboy]

I had thought about that... The issue is a difference in ground potential on the two circuits, yes? so is the solution to connect the two "grounds" together?

Would that connection be made in the breaker box? or between the two outlets involved? (that is, run a thick copper cable from the ground prong of the projector to the ground prong of the rest of the system?

(it's hard to explain spatial concepts in print)

I do like the cat5 solution. fast, easy.

[pdc]

You have a serious electrical problem. I would fix it. It is against the NEC to lift AC grounds.

The best thing to do is to have all interconnected audio and video gear on the same phase, using a Star Ground. If you are using a star ground system, all component outputs should have a balanced audio cable with all three contacts in tact, with the grounds lifted on all inputs. If you do it the other way around, you will have some nice RF and/or noise introduced into the audio path. Make sure than you do not have multiple grounds, or that you are grounding to plumbing. I have seen people try to do this, grounding to a piece of metal pipe that ultimately terminates to PVC before it hits the ground. That does not work.

I would make darn sure that you are not connecting to components on two different phases. Connecting the ground between the two would be no different than what you have now and would yield the same result.

The other concerns are moving anything electro-mechanical and all ballast lighting from the A/V phase. All of the electro-mechanical discharges through the ground.

If everything else is correct and you still have issues, you could just install an AC isolation transformer.

[bladeaudio]

This is what you need....

http://www.bhphotovideo.com/c/produc..._Isolator.html

[pdc]

Or, one hour with an electrician and a screwdriver.....

[Frank DeWitt]

It is possible, even common to have a ground loop problem without having anything wrong with the electrical wiring. It may be fixable in one hour but many times it is not practical to fix it in any number of hours.

Frank