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Audio - Eliminating earth loops

Discussion in 'Hobby Electronics' started by JERD, Sep 30, 2009.

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  1. JERD

    JERD Guest

    I have a friend that has a sound desk and one input to it is from an
    electronic organ that produces a nasty earth loop (buzz) problem not 50
    hertz mains.

    Temporarily lifting the earth off the organs mains transformer completely
    eliminates the problem, but this not a genuine or safe 'fix'.

    I recall seeing an article in some electronic magazine some time back of a
    240v mains unit that could be put in line with either the sound desk or the
    'equipment' but can't now recall where I saw it!

    Can someone please offer some suitable suggestions to rectify this problem?

    A mains isolating transformer should do the trick, but am wondering if there
    is some other cure?

  2. Phil Allison

    Phil Allison Guest


    ** Best idea is to provide the organ with a balanced output connection.

    Get one of these fit it inside the organ near the existing jack output:

    Wire the 10kohm side to the jack and the 600ohm side to a stereo jack or a
    male XLR.

    The ground terminal of the stereo jack or pin 1 of the XLR can be left
    unconnected to eliminate ground loops.

    The signal from the transformer can now be fed into a mic input or line
    input on the audio desk.

    ** The organ already has one of them.

    ..... Phil
  3. Mr.T

    Mr.T Guest

    Even cheap DI boxes have a ground lift switch, which leaves the instrument
    grounded, but isolated from the mixer ground.
    Have you tried that yet?

    Why not, good quality audio transformers are routinely used in pro audio,
    and don't cost the earth.
    Studio quality is more expensive, but unnecessary in this case.

    That's for sure.

  4. Phil Allison

    Phil Allison Guest

    "Bruce Varley"
    ** Long as the 10k to 10k tranny is installed at the receiving end on the
    link - the signal quality is normally fine.

    The little trannys in a metal can sold by Altronics ( M0705, M0706 etc) are
    a good example.

    ** Very few keyboards these days would use a mains earth connection, they
    mostly either use plug-pak adaptors or are of "double insulted"
    onstruction - so the one alluded to by the OP must be nearly antique.

    ...... Phil
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