Laptop noise down the PA

[GCT]

Hi
Have a problem with running an audio visual presentation from a laptop and projector into the PA. Running the laptop on battery is fine but as soon as the charger is connected there is a load of computer noise pouring in. I've had this problem with other laptops too. I tried changing phases and on one different mains phase it's quiet - on the other 2 noise appears which is an intriguing result. Any idea what's happening and how to resolve this if we only have one phase?

Cheers

GCT

[timc]

It's the switchmode PSU that spews hf noise bak out onto the powergrid and through the computer as well. A linear psu will do the trick.

[Earl K]

> It's far far easier to simply put ( galvanic ) electrical isolation between the two parts of your system causing the noise ( the PC & "the next stage/whatever that is" ) using something like this ;

http://www.rapcohorizon.com/images/Product/medium/lit100_front.png (http://www.rapcohorizon.com/p-18-lti-100.aspx)

> Or if you can solder ( buy 2 of these transformer isolators & make your small stereo iso setup / by constructing a special cable using a 3.5mm jack to (2) XLRmale ends ) ;

http://www.rapcohorizon.com/images/Product/medium/isoblox_front.png (http://www.rapcohorizon.com/p-373-isoblox.aspx)

<> cheers

PS ; This thread really should be moved / the OP may not realize that this is a not LANSING specific topic .

[Mike Caldwell]

You need some form of isolation between the lap top and the input to the PA system. The Rapco unit pictured would work or just about any direct box "DI" as we call them in the live sound business. The PA company should have had some available to use. General instrument DI's have 1/4 inch inputs so you would need to have an 1/8 inch tip ring sleeve cable that breaks out into two 1/4 inch tip sleeve (mono) plugs or a little easier to find the 1/8 cable that breaks out into two RCA male plugs and use a RCA to 1/4 inch adapter.
Many DI box companies offer specialized versions just for laptops, mp3 players, etc. that have RCA and 1/8 inch inputs. Rapco, Whirlwind, Radial all have models for what you need.

Or you could have Mike Caldwell Audio Productions supply the sound system for your next presentation and I'll take care of you:D

[GCT]

Thanks a million

GCT