Eliminating ground loop/mains hum? (BluRay->Projector)

Phil99 · 9 Jan 2010 at 22:16

Hi all,

I've got an Optoma HD700X projector, a Sony BluRay player and a Cambride Audio 640Av2 amp.

Connecting from Sky box -> amp and PC -> amp both seem fine (using monitor/TV as display).

When the projector is attached to the BluRay player and then the BluRay player is attached to the amp I get a very annoying mains hum. Removing the HDMI cable from the projector gets rid of the hum. I get the same issue with component to the projector.

Removing the earth from the power strip that goes to the projector seems to reduce but not eliminate the hum, but this is not a solution for the obvious safety issue (and the fact the problem still remains, albeit to a slightly lesser extent)

I've tried plugging the projector into the same 4 way extension as the player and also tried plugging them into separate wall sockets but the problem is the same both ways round.

So, question is, is there an affordable and safe way of sorting out this issue?

whitecrook · 10 Jan 2010 at 00:02

I understood the basics of earth loops, but this pdf provides a clear explanation.

You need to try and narrow it down even more. Is it only the blu ray + amp + prjector combo that does it? PC+amp+projector fine? PC+projector? blu-ray and projector? i.e. is it the blur ray or the proj that seems to affect it.

Do you HDMI cables have the ferrite rings on the cable? try to fit some if not, or get a cable that does.

Try if possible to plug the equipment in to different circuits (i.e. on the breaker box) Most houses have upstairs and down stars on a different circuit.

Sinopa · 10 Jan 2010 at 00:28

Ferrite rings will do nothing for mains hum.

Which items of the equipment have 3-core mains leads?

Phil99 · 10 Jan 2010 at 01:11

Projector and Amp have 3 core, bluray has 2 core.

No problem at all when the bluray player is plugged in to the amp with no connection to the projector.

As soon as the projector is plugged in to the mains the humming starts. I've just noticed that I have a similar problem with my monitors (via HDMI, 3 core plug to the monitor), but it's not half as bad as the projector (i.e. I have to turn the volume up higher to notice the hum, probably higher than I'd ever want to play a film at).