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How isolate two earths on electronic equipment?

Discussion in 'Electronic Components' started by Sammy, Mar 23, 2006.

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  1. Sammy

    Sammy Guest

    I am in the UK. I want to know how to reduce hum & buzz when
    connecting two items together.

    --------

    I have two pieces of electronic equipment (a PC and a tape
    recorder) that I want to connect so that a signal from the tape
    recorder is fed into the PC.

    However if the two earths are connected then I get a buzz and hum.
    This does not seem to be induced on the screened cable because if
    I take the line output rather than the earphone output using the
    same length of wire for each then the line out is clean (but too
    weak to use).

    The PC has an earth in its mains lead. The tape recorder has only
    two mains wires in its mains lead with no earth.

    ----------

    I am told there are adaptors I can use in series with the signal
    lead which will stop the buzz & hum. I believe such an adaptor
    isolates the two earths from one another.

    An example of such a product is the Retell (model 142) Connector.
    http://www.telephonerecorder.co.uk/recording/accessories/142.htm

    How does such a connector or adaptor work ???

    Surely it's not simply a matter of cutting the earth lead such
    that it is no longer continuous between the tape and the PC ???
     
  2. crazy frog

    crazy frog Guest

    try 2 power diodes in parallel, with each
    diode conected as cathode to anode on
    each end with a .1uf greencap accross them.
    sometimes works, this seperates the mains earth
    from signal aerth.
     
  3. sQuick

    sQuick Guest

    Whatever you do, don't remove the earth connection. This is not the
    way to fix the problem and could be dangerous.

    Try disconnecting the screen of the cable at the tape end, this should fix
    it.

    The line out from the tape deck should give a good signal when connected
    to the computer line in. If you are feeding the headphone output into the
    computer line in you are going to get noise & possible distortion.

    sQuick.
     
  4. crazy frog

    crazy frog Guest

    the diode trick has this done in the
    marshall power amp 2/ch model 9200
     
  5. crazy frog

    crazy frog Guest

    the diode trick has this done in the
    marshall power amp 2/ch model 9200
     
  6. bg

    bg Guest

    Sammy wrote in message ...
    Your problem is called a ground loop. It is caused by current flowing from
    one chassis to another thru the shield of the cable. You have two options -
    connect a heavy ground strap from one chassis to the other to provide a path
    for ground current other than the shield. Disconnecting the shield at one
    end will help.
    #2 - transformer coupling - this is what the adaptors do for you. Sometimes
    they are called hum eliminators
     
  7. n

    n Guest

    If there is a radio shack, get a stereo isolation transformer. They have
    RCA plugs on each end. Used for cars that have a power amp in the trunk. I
    use them from my PC to my home entertainment system. There available by
    mail order too. Cost is about $20 US.
     
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