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Discussion in 'Electronic Basics' started by Music Man, Feb 26, 2005.

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  1. Music Man

    Music Man Guest

    I wonder if anyone could help.I would like to know how the earth
    ground loop problem enters an audio signal?
    For instance if I plug my guitar into a mixer input(via DI) why does
    the hum enter my signal.
    Could you explain how the AC current from the mains distributes it
    voltage to the mixer circuit and the guitar channel in question and
    how the earth is used in the unbalanced signal.
    I'm also having trouble with terms like ground and earth.If something
    is ground to a chassis or the mains earth.What different functions do
    they have?

  2. w_tom

    w_tom Guest

    Many types of grounds exist. For example the instrument may
    have two grounds. One that is the negative side of signal or
    power. The other that is the instrument body. Both may
    eventually connect to a common point. But they remain
    electrically different grounds. Why? Wire is an electronic
    component - not just a conductor.

    A building has two ground systems that share some common
    wires. One is safety ground primarily installed for human
    safety. Safety grounds are also often routed so that noise is
    carried away. Safety ground must also connect to earth
    ground. A wall receptacle is safety ground. It may connect
    via electronic components (wires) through circuit breaker box
    to earth ground. But safety ground and earth ground are two
    different concepts.

    Many make a mistake of assuming wire is a perfect
    conductor. Therefore they assume earth ground and safety
    ground (sometimes called equipment ground) are same. They are
    not, just as DC ground inside that amp is not same as earth
    ground or safety ground. Yes that DC ground eventually
    connects to safety ground. But again, is is a different
    ground often connected to safety ground at only one point.

    For eliminating noise, the same concept: single point
    grounding. It gets complex when other electronic conductors
    such as humans get into the circuit. We try to eliminate the
    human (and other) created problems by using single point
    grounding and better conductive paths (wires). For example,
    guitar and mic might use same single point ground at the amp.
    Then the amp shares a single point ground with all other
    equipment at the power distribution strip. That power strip,
    in turn, shares a single point ground at the wall receptacle
    OR where all safety grounds meet back at circuit breakers.
    Then that circuit breaker box shares a common earthing ground
    with concrete under your feet.

    Yes, even concrete is a conductor of electricity. How
    conductive determines how much it affects your ground
    network. More specifically, what type of electric currents
    might be passing through it. To a mic signal, concrete is not
    a conductor. To AC mains electricity, concrete might be a
    conductor. To static electricity, concrete is a good

    Try to keep things simpler - using single point grounding on
    the most conductive electronic components - the wires. Good
    conductors sharing single point ground techniques make less
    conductive paths less relevant - ie. eliminates hum and ground
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