Earth hum on a new imac

Discussion in 'iMac' started by ian hall, May 15, 2009.

  1. ian hall macrumors newbie

    Joined:
    May 15, 2009
    #1
    I have a long 3.5mm phono cable going from my headphone out to an input on my hifi amp. With the iMac muted and with the volume down on the amp i have a distinct hum through the speakers. Its even there when i have the amp switched to another input source. Don,t think its the lead as the noise goes if i disconnect from the imac.
    How do you folks connect to external speakers if not like this?

    Thanks

    Ian
     
  2. mstam macrumors member

    Joined:
    Apr 20, 2009
    #2
    That's a grounding issue. If there's a difference in the impedance between your Mac and the amplifier, a current will flow over the ground causing a humming sound. This is also often caused by a low impedance between the ground and signal line of the amplifier that can only be solved by getting a better one.

    For now, make sure the power plugs of the Mac and amplifier are both ground and connected as close to each other as possible.
     
  3. ian hall thread starter macrumors newbie

    Joined:
    May 15, 2009
    #3
    All of the equipment is earthed (grounded-i,m from the uk!!!) and is on the same electrical circuit. The imac is 5 metres from the hifi.
    Anyone else had similar probs?

    Ian
     
  4. mstam macrumors member

    Joined:
    Apr 20, 2009
    #4
    Get yourself an impedance meter and if the resistance between the signal and ground is much less than 100 ohms, the issue is with your amplifier.
     

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