Hum from my external speakers...

Discussion in 'MacBook Pro' started by phalewhale, Jul 6, 2007.

  1. phalewhale macrumors 6502a


    Jun 10, 2007
    No they don't smell, but they do make a low level humming noise.

    I've just upgraded from an iBook G4 to a MacBook (white with superdrive). The only downside I've noticed so far to upgrading is that I have my notebook connected to an external amplifier and set of speakers. If the MacBook is plugged into the mains all is fine but if I unplug it to let the battery drain, I find that my external speakers give off a low level hum which is really annoying!

    As soon as I plug the power adapter back into my MacBook, it goes away.

    It never did this on my iBook, or the Dell 6400 inspiron I had. Any ideas?
  2. kolax macrumors G3

    Mar 20, 2007
    Static noise probably.

    The best way to avoid any interference is to take advantage of the optical out port on your MacBook - if your amplifier has an optical in on it that is.

    Any analogue connection suffers from static interference - try turning a hair dryer on while watching TV on an analogue signal.

    Also, the sound quality will most likely increase since the digital to analogue converter on your amplifier will be much better than that in the MacBook.
  3. phalewhale thread starter macrumors 6502a


    Jun 10, 2007
    But it didn't happen with my old iBook. Just found another thread so I will post there. Here's the new thread if anyone can offer any help.

  4. Edge100 macrumors 68000

    May 14, 2002
    Where am I???
    This sounds exactly like ground loop hum. It's caused by having more than one path to ground. (also see here for details)

    The external amp has a path to ground, as does the computer when plugged in (or when running on battery power), and the audio cable has its own ground wire. The problem arises when these grounds are not the same; this creates an electrical potential difference along the ground (which, by definition, should be the zero point).

    Solution? Always have your electrical devices sharing a common ground. Your external amp should be plugged into the same outlet as the computer, therefore ensuring that the ground potential is the same for each.

    Alternatively, you could remove the ground from the audio cable, the computer, or the amp. BUT, this is NOT ADVISED because if you happen to touch the device while its on, YOU become the ground, and very nasty things can ensue!

    Electrical wiring is important when dealing with audio. Always plug your audio devices into the same outlet to ensure identical ground potentials.
  5. TechnoFaz macrumors newbie

    Oct 14, 2008
    Midlands UK
    I solved my macbook ground loop hum

    Try using the longer extension mains cable lead with your macbook power supply, Keep the macbook power transformer further away from your speaker power supply. This worked for me. :)
  6. patrickkidd macrumors newbie


    Mar 11, 2010
    Sausalito, CA

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