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Sound (earth?) hum..... arrrggghhh!!!!


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Wondering what any of you guys have done if you've come across this problem.


School Hall.


We have a projector in the ceiling linked to a PC and DVD player. Sound wise I have it through a tiny 4 way passive mixer that the plebs teachers can use for volume control.

That connects to a channel of a 6 way line/mic mixer and power amp that lives backstage, that also has a radio mic connected to that they cannot control the level of.


I have had to install a GLI in line with the PC to stop the dreaded PC hum :)

However, as soon as the DVD is powered up.... HUM, I installed another GLI in line with that which helped, but it's still there.

The hum stops completely if I disconnect the composite video lead from the player :blink: which isn't exactly helpful :o


My next plan was to try a video GLI, I think CPC have them at a reasonable price. Anyone know if that will do the trick?


I've been trying GLI's all over the place and disconnecting bits of kit but getting nowhere, short of starting to remove earth cables from plugs, which I'm not about to do!


Pleeeeeeaaassseeee!!!!! any ideas!!!! What little hair I left have is going fast.... ;)


It's all down to this darn pesky video connection :(


Funny how it only does it when the DVD player is powered up. (as oposed to just connected, bearing in mind they are never truely off whilst plugged in to the mains)

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You need to have power for everything plugged into one source - you are getting an earth loop from the projector in all probability.




De Novo Events


I think it is. AFAIK the same ring main, but will double check. The projector is actually plugged in to the same 4way as the amp :unsure:

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Yeah go for the isolator on the video. It's common on CCTV systems as well, where mains cameras are strung across large sites and connected every which way... in silent systems the hum loop can manifest as wavy bars on the screens.
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