Projector causing ground loop with Rotel gear

[greenjudas]

I realise ground loop problems have been covered before,but would appreciate any advice for my particular situation.
I have a RSP 1066 /RMB 1075 combo and have never had a problem[except for making me buy a heap of cd's and dvd's because of its SQ].The problem has been introduced by the new projector.I originally hooked it up via the 1066 and the hum was terrible but by going straight from dvd to projector it was fine.The problem now is free to air tv when wanting to watch the football on the big screen.I don't have a STB yet,so am using the vcr at this stage.As soon as I connect vcr to projector,I get the hum, which can be partly corrected by turning the sub down,but still hums from the rest of the speakers. Would it be the fan in the projector causing this,and if so,any ideas to fix??

Cheers

[bleeding ears]

This one has em stumped! LOL

Anyone ????

[sirbogey]

I find it hard to believe that the projector is causing this. I've been using my Optoma EzPro 753 projector for 4 years, in different setups and never came across any interference coming from the projector. I even lived in different countries with different power voltages, but the same Rotel gear and the same projector. The only problem ever with the Rotel RSX-1055 and the projector, was a horizontal line being projected onto the screen moving in the upper direction. This was caused by the grounding (the third prong on your power plug from the projector). A trip to a high end shop helped out: I was told this was common. It's supposed to cause all kind of interference problems. I was told to cut the third prong. If you need more info on how to do it safely let me know. :dothewave:

[Kevin D]

I was told to cut the third prong. If you need more info on how to do it safely let me know.

This is not the correct solution, and there really isn't a safe way to do this. The ground lug is there as a safety feature and removing it kills it. While this may remove the interference, you haven't solved what's wrong.


GJ,

Assuming that the projector is on a different circuit and/or plug then the rest of the equipment, run an extension cord from the projector to the outlet where the Rotel stuff is plugged in. If that makes it go away, you will need to check all the grounding on both outlets and the panel, or move the projector plug onto the same circuit as the equipment.

Kevin D.

[sirbogey]

This is not the correct solution, and there really isn't a safe way to do this. The ground lug is there as a safety feature and removing it kills it. While this may remove the interference, you haven't solved what's wrong.

Won't argue with that. 2 outlets of course. But I still don't understand your "safe" solution, nor your explanation to GJ?! Extension cable won't help.

[wkhanna]

I can’t really give ‘expert' advise, but I think what Kevin is trying to determine is if you are supplying the projector on a circuit that is separate from the other complements. If this is the case, the two circuits may actually have different potentials on the ground wire lead. Just because it says ‘ground’ does not mean there is ‘0’ voltage. If one has circuit has slightly different potential (voltage) on the ground line, then it could cause the hum.

Running an extension cord from the same circuit your system uses to the projector will eliminate any variation in ground potential between the components, if one exists.

I’m just guessing, and am sure Kevin will set us all on the ‘right’ path!

[greenjudas]

Kev,I tried doing what you advised but that didn't fix the hum.I have played around a bit more and now am really confused!By turning off the sub at the powerpoint,it has gotten rid of the hum from the sub and all the speakers.Bare in mind that there was never a hum with this sub ,which I have had for 2-3 yrs,until recently with the introduction of the projector Any ideas?

[Kevin D]

wkhanna helped explain my rushed 'on lunch' response pretty well. Thanks.

As he explained, the extension cord wasn't a solution, it was a way to narrow down whats causing the problem.

With that out of the way, if you unplug the sub from the wall (or powering it off) the hum goes away.. Is your sub plugged into a different outlet then the equipment and/or projector? If so, you can try running the sub off the projector and/or equipment outlet?

Ground differentials will always take the path of least resistance, which isn't always the shortest path! The way the components in the system are designed also has an effect on it. It sounds like there an issue at one end. Having both the sub and projector plugged in completes the path. The hum is travelling along all cables that tie the components together. So sub + Rotel everything handles it fine. Projector + Rotel, same thing. Tying all three together creates a path that shows up as a hum.

Re-reading your first post, it seems the hum really gets introduced why you connect cable to the system. Cable systems are the number one cause of hum out there. They're usually improperly grounded as they come into the house and cause havoc. If just unplugging cable from the VCR solves your problem, you can call the cable company and try to have them fix it, or get an isolator from Jenson ISO-MAX or partsexpress.com.

Let us know what you find.

Kevin D.