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Electrical isolation for A/V

Discussion in 'Electrical Engineering' started by Les, Jun 1, 2006.

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  1. Les

    Les Guest

    Does anyone know how to properly run circuits for audio equipment, so that turning other items on or off in the house, do not affect audio (ie, such as ceiling fans or items like that).
    I've had electricians say that everything needs to go to a common ground. I've heard others say that everything needs separate grounds. So what's the right approach to avoid any interference with audio/video equipment?

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  2. Roy L. Fuchs

    Roy L. Fuchs Guest

    Put an exercise bike with an AC alternator hooked up to each one, and
    feed each unit its own power source.

    Of course, you need lots of naked women on the bikes when you need
    it all fired up at once.

    All that, just to watch a movie!
  3. Beachcomber

    Beachcomber Guest

    As a general rule and practice, AC circuits should follow the National
    Electric Code (or local variant) with standard safety grounding

    Pro-Audio circuits are generally balanced mic level and line level
    signals that should be run in audio cables with a shield (audio
    ground) and drain wire. The connectors are typically XLR or Stereo
    1/4" jacks.

    Whether the audio ground should be connected to the device or not
    depends on the circuit, the presence or absence of jack fields, etc.
    but generally there is a break in the audio ground connection either
    at the jack field or the device.

    Consumer and Semi-Pro audio devices are often unbalanced (typically
    connected with RCA connectors). These are less desirable for long
    distances and sometimes more prone to picking up hum from external
    fields (especially if cheap cables are used). It's hard to avoid
    these since there are so many inexpensive devices that used unbalanced

    Microphone cables often require special consideration since the audio
    level is typical -40dB from a line level connection and more easily
    prone to pick up hum and noise from external fields.

    Some Pros use a special balanced mic cable with 4 conductors and an
    audio ground arranged something like this.

    + +
    - (Audio Ground/Shield not shown)

    The beauty of this arrangement is that the geometry cancels the
    magnetic fields (both induced and projected) of the mics + and -
    connectors and the line is especially quiet when it comes to noise.

    Keep any audio cables away from inductive devices (fluourescent
    lights, fans, motors, computer power supplies, transformers, etc. and
    you should be OK.

    Of course the ultimate connections are now digital and fiber-optics in
    many cases, the latter having the advantage of not having any
    interference with AC circuits whatsoever.


    Use common sense. You don't want to run any audio cables parallel to
    power lines (such as wire tying them to electrical conduits).
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