# Background Noise when PC line out sent to PA.



## JonathanAnon (Dec 17, 2004)

I get a lot of background noise when I connect my laptop to my PA mixer. 
This only happens when my laptop is connected to a power source. There is no noise when I plug it out and run it off the battery. 
Can anyone explain why this happens and what I can do to fix it?


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## cwwozniak (Nov 29, 2005)

Is the background noise a loud steady hum? If so, it is probably caused by undesirable AC currents in the audio cable shields. The currents are caused because the chassis grounds of the PC and PA system may be at slightly different voltages. Disconnecting the AC power for the laptop floats the laptop's ground at the same voltage as the PA system ground.

You could get fancy and get the hardware to make a fiber optic (S/PDIF) link from the PC to the PA system. There is no metallic connection of any kind between the PC and PA system.

A simpler and less expensive approach might be tor try a ground loop isolator.


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## JonathanAnon (Dec 17, 2004)

Hey thanks for your reply. The noise is not a hum, but is more random, kind of sounds like a PC booting. Let me have a look at your suggestions and see is there any of them that will work. 
thanks.


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## cwwozniak (Nov 29, 2005)

Any chance the laptop has a built-in microphone that might be on?


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## JonathanAnon (Dec 17, 2004)

No laptop microphone. Turned down all inputs/outputs on the recording/playing and still noise.


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## cwwozniak (Nov 29, 2005)

Does the laptop have built-in speakers? If so can you hear the noise through them with volume cranked up all the way, the laptop running on AC power and the PA system unplugged from the laptop?


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## JonathanAnon (Dec 17, 2004)

Laptop has built in speakers. BUT, I never hear this noise through them when they are cranked up all the way. It is ONLY with the PA plugged in. thanks for your help.


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## cwwozniak (Nov 29, 2005)

JonathanAnon said:


> I never hear this noise through them when they are cranked up all the way. It is ONLY with the PA plugged in.


I just wanted to eliminate any chances that laptop was generating the noise internally when operating from AC power. The ground loop isolator _MAY_ help out to eliminate the noise.


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## JonathanAnon (Dec 17, 2004)

Hi, 
I forgot that most DJs now use their laptops for DJing so I googled a DJ website and there seems to be noise suppressors out there for doing just this. The ones I found dont have the connection that I'm looking for but I'm going to an electrical shop today to see if they can suggest something. 
thanks, 
J


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