Help! Macbook pro 15" Hum/noise

Discussion in 'MacBook Pro' started by sallamir, Mar 11, 2010.

  1. sallamir macrumors newbie

    Joined:
    Mar 11, 2010
    #1
    Hello guys, I bought my MBP around 3 weeks ago, everything is fine except the sound output, when my speaker is connected to the lap top it hums during and after(around 30 seconds after the sound then the hum will goes away) any sound come out from the lap top, let's say I am playing music, in background i have the hum, when the music finish there is hum around 30 seconds then no more hum. Even if there is small sound plays in the laptop it's with hum (ex. i receive new email which cause small beep or buzz to notify me there is new email then this hum also starts.)
    It's really annoying, I really don't know what to do. I disconnected the charger but no changes at all. This thing only happens with external speaker, with internal speakers and headphones there is no hum (My speaker is fine there is no hum with my other laptop).

    I appreciate if anyone can help me.
     
  2. m85476585 macrumors 65816

    Joined:
    Feb 26, 2008
    #2
    It sounds like you are using amplified (powered) external speakers.

    It's interesting that the hum does not go away when you unplug the charger. That would seem to eliminate a ground loop. Is the hum still present if nothing except the speakers is hooked up? Disconnect anything the plugs into any ports, including USB devices, network cables, and external monitors, and the charger and see if the hum goes away. Just to rule out any possibility of a ground loop, if the speakers have a grounded (3-prong) power supply, you could try an adapter like this to isolate them from ground. Make sure the metal tab does not touch the screw in the center of the outlet as that will just connect them to ground again.
    http://www.summitsource.com/images/products/ACS100.jpg
    You can buy one of these for a few dollars at your local hardware store.

    When you play a sound, the audio chip goes into active mode, and it has some noise on the output. When there is no sound playing, it is in inactive mode and seems to disconnect or short the output, and any background noise goes away. I can hear the audio chip go from active mode to inactive mode some time after a sound stops playing just from the background noise I can hear on my headphones, and the timing you describe (around 30 seconds) sounds about right.

    What volume do you have the MBP's output set to? If it is very low, try increasing the volume on the MBP and decreasing the volume on the external speakers. That will cause the speakers to amplify less noise.

    If none of that helps, there might be a problem with the sound output on your MBP. Since the speakers don't make noise connected to anything else, that should rule them out.
     
  3. sallamir thread starter macrumors newbie

    Joined:
    Mar 11, 2010
    #3
    Thanks for your help, I tried all of the things that you said except the adapter which i don't have now, and none solved the probelem :(
     
  4. sallamir thread starter macrumors newbie

    Joined:
    Mar 11, 2010
    #4
    Finally it solved, thanks dude.
    the problem was the cable of my speaker which goes to output jack, I must change the cable, because now I tried with my friend's cable no more hum.. :D
     

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