djmatthill Posted December 10, 2014 Share Posted December 10, 2014 I have a Sanyo plc 15 projector plugged into a laptop via Vga cable .. The laptop is connected to usb soundcard then into the mixer .... The mixer has balanced xlr outputs to tbe amp... So all ballanced. All works fine until I plug the Vga cable in and I get an almighty buzz which changes in pitch depending what the projector is showing... Interestingly if I'm showing a black screen the buzz virtually vanishes.... Ant ideas ? Matt Link to comment Share on other sites More sharing options...
David Lee Posted December 10, 2014 Share Posted December 10, 2014 Have you tried the laptop without the power lead in (running on batteries)? Link to comment Share on other sites More sharing options...
djmatthill Posted December 10, 2014 Author Share Posted December 10, 2014 Yes mate first thing I tried as had that before with another laptop, still there when on batts. Link to comment Share on other sites More sharing options...
Oldradiohand Posted December 10, 2014 Share Posted December 10, 2014 DI box between projector and mixer? what is the audio source? could you take the audio feed from there? via a DI box? You could try lifting signal earths but NOT mains earths. Link to comment Share on other sites More sharing options...
revbobuk Posted December 10, 2014 Share Posted December 10, 2014 Try plugging the projector power in somewhere else. VGA does produce an awful lot of hash on ground cables. Has the VGA lead you are using got ferrite cores on it? Any chance you can run HDMI to the projector instead; sometimes you get better results that way. I'm sure you have already checked, but make sure that your balanced cables are all properly wired, with no links between connector shells and screen. And does the USB soundcard have balanced out? Many don't. You don't have to use a DI box between soundcard and mixer - that forces you to drop signals to mic levels rather than line - but you could try adding isolation at that point, especially if the sound card is unbalanced output. What sound card is it? Link to comment Share on other sites More sharing options...
djmatthill Posted December 10, 2014 Author Share Posted December 10, 2014 Audio comes from laptop by usb to a denon soundcard and midi controller ... Then from midi controller/soundcard four outputs are fed by rca phono to a mixer which is then connected to the amp by balanced xlr (2 Chan)... Where are you suggesting I should Insert a DI here mate ? Matt Link to comment Share on other sites More sharing options...
David Lee Posted December 10, 2014 Share Posted December 10, 2014 Have you tried changing resolution to see if noise changes? Link to comment Share on other sites More sharing options...
djmatthill Posted December 10, 2014 Author Share Posted December 10, 2014 It's a denon dn-hc4500 It's a denon dn-hc4500 All xlr cables are ok and checked... I also have the same issue if I use my Vga to composite scan converter too ??? Link to comment Share on other sites More sharing options...
pete10uk Posted December 10, 2014 Share Posted December 10, 2014 Audio comes from laptop by usb to a denon soundcard and midi controller ... Then from midi controller/soundcard four outputs are fed by rca phono to a mixer which is then connected to the amp by balanced xlr (2 Chan)... Where are you suggesting I should Insert a DI here mate ? Matt You need to add a di between the RCA outputs and the mixer. That should sort you.CPC and Maplin do a cheap RCA inline unit designed for car use. I've used them a number of times with good results. Link to comment Share on other sites More sharing options...
djmatthill Posted December 10, 2014 Author Share Posted December 10, 2014 I'll give that a go and see what happens Link to comment Share on other sites More sharing options...
bruce Posted December 10, 2014 Share Posted December 10, 2014 pedant: that RCA unit is an isolating transformer, not a DI. But it'll do the job.... Here's one of the CPC ones - and there are plenty on ebay at similar prices. http://cpc.farnell.com/_/b070/ground-loop-isolator/dp/CP03283 Link to comment Share on other sites More sharing options...
pete10uk Posted December 10, 2014 Share Posted December 10, 2014 pedant: that RCA unit is an isolating transformer, not a DI. But it'll do the job.... Here's one of the CPC ones - and there are plenty on ebay at similar prices. http://cpc.farnell.com/_/b070/ground-loop-isolator/dp/CP03283 They're the ones. Sorry yes they are isolators not di's, they do the same job but output an isolated unbalanced signal not a balanced signal. Heres a link to a in stock item. Maplins also do them, a bit more money I think but you can pick one up. http://cpc.farnell.com/unbranded/fga-40/ground-isolator/dp/AV19955?crosssellid=AV19955&crosssell=true&in_merch=true& Link to comment Share on other sites More sharing options...
laolu Posted December 11, 2014 Share Posted December 11, 2014 I'd lift the ground (earth) of the projector. I know it is against the rules, but just to chek it out... If the almighty buzz disappears, you got yourself a ground loop. B-) Norbert Link to comment Share on other sites More sharing options...
djw1981 Posted December 11, 2014 Share Posted December 11, 2014 if you are suggesting the mains earth the DON'T. If you are suggesting lifting pin 5/10 on the VGA, I;m not sure that will achieve anything. lifting the ground on the audio lines may help but only signal, not mains. Link to comment Share on other sites More sharing options...
MarkPAman Posted December 11, 2014 Share Posted December 11, 2014 If the almighty buzz disappears, you got yourself a ground loop. Or you've just killed your self! Link to comment Share on other sites More sharing options...
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