power noise through speakers? (audio noob question)

Discussion in 'Computers, Cabling & Other Miscellaneous Hardware' started by penguineer, Sep 20, 2012.

  1. penguineer

    penguineer Full Time Elf

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    [This *seems* to be the most appropriate area to put this in.......]

    This will be a pretty basic audio-visual noob problem.....

    I've just bought one of these - http://www.jaycar.com.au/productView.asp?ID=AA0472 - as a basic amp to run my speakers at the fence.

    After I hooked it up to the speakers and my show laptop this evening to just try it out I noticed a humming noise through the speakers.

    It doesn't appear to be the speakers as I can connect them "more directly" to the laptop and not get the noise.

    When I connect the speakers to the amp with no extra wire or inputs I still get the noise.

    At low volumes the noise is a bit distracting and I'd prefer it wasn't there.

    Is there anything I can do about this? Do I just live with it, or is the amp faulty?

    Thanks for any help!
     
  2. David_AVD

    David_AVD Good news, everyone!

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    My guess is that it's switchmode noise induced from the laptop's power supply. Get it up and running (with noise audible) then unplug the laptop from it's power supply. If the noise disappears, then you've found the culprit.

    Once you've done this test we can go from there. :)
     
  3. OP
    OP
    penguineer

    penguineer Full Time Elf

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    Sounds like you've played this game before :)

    OK - I've put the rig together on my workbench where I can lay it out a bit better and make sure things are connected as I think they are at any time(gets confusing).

    Anyways:

    - NOT connected to laptop I get a very low hum that's hardly noticeable unless the amp volume is turned the whole way up, probably not going to get rid of that and can be lived with.

    - connect to laptop and I get a louder hum with more of a crackle in it, noticeable and annoying at all volumes

    - disconnect the laptop power brick(so laptop is running on batteries) while running the speakers, the noise goes away

    So - it does look like the laptop power brick is causing the problem.......

    Any ideas from here? Can I shield things somehow?

    Cheers!
     

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