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Telephone PC Interface

Discussion in 'Electronic Repair' started by Jay, Sep 14, 2004.

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  1. Jay

    Jay Guest

    I am trying to find a way to record telephone conversations to my PC,
    (legal, for training purposes only). I have an interface that plugs
    into a cassette recorder and that works fine on the cassette. I have
    tried this same interface plugged into my computer, either line-in or
    the microphone jack, but when I record I get a loud hum noise and I
    can faintly hear myself in the background, though I have to talk or
    whistle loudly to do so. Apparantly I need a different interface. I
    have found them for sale for around $50, but I would prefer to make my
    on, usually these interfaces use fairly simply filter circuits. Any
    suggestions?

    Thanks
     
  2. Stan

    Stan Guest

    (Jay) wrote:

    }I am trying to find a way to record telephone conversations to my PC,
    }(legal, for training purposes only). I have an interface that plugs
    }into a cassette recorder and that works fine on the cassette. I have
    }tried this same interface plugged into my computer, either line-in or
    }the microphone jack, but when I record I get a loud hum noise and I
    }can faintly hear myself in the background, though I have to talk or
    }whistle loudly to do so. Apparantly I need a different interface. I
    }have found them for sale for around $50, but I would prefer to make my
    }on, usually these interfaces use fairly simply filter circuits. Any
    }suggestions?

    Yes...google.

    Try: phone computer record interface circuit

    Stan.
     
  3. Dana Raymond

    Dana Raymond Guest

    I suspect the problem is a grounding one. If you plug into the microphone
    input of your cassette recorder and all works well and then move the plug
    over to your computer mic input and all you get is hum, then check to see if
    your 'interface' is powered. If it is, use an isolation transformer or
    temporarily run it by battery. If it then works, you can sole the problem
    permanently.
     

  4. If your in a real hurry take apart an old modem, lots o filter coupling
    parts, and hey they work with phones. Try running the phone line to a
    modem(no power to it) and pick the signal off the matching/isolation
    transformer output use the soundcard line in.

    With a little post processing to even up levels and some VOX software to
    conserve disk space I had 100's of hours of conversations.

    No, I didn't learn much of the subtleties of phone interface circuits but it
    took only minutes and cost me some old hardware from the junk box.
     
  5. Soundcards don't take the same kind of microphones as tape recorders. A
    tape recorder or PA system takes a microphone that outputs about 1 mV. A
    soundcard supplies power through a resistor to a transistor inside the
    microphone, amplifying the sound level to about 30 mV.

    A few years ago I published an article and circuit in QST (the ham radio
    magazine) about how to use a traditional microphone with a soundcard. It's
    a 1-transistor amplifier. I don't have the circuit or the exact reference
    handy.
     

  6. How about this?

    http://www.modemspy.com/en/index.php
     
  7. Ross Herbert

    Ross Herbert Guest

    On Wed, 15 Sep 2004 22:20:02 GMT, "Carl Wedekind"

    |
    ||>I am trying to find a way to record telephone conversations to my PC,
    |> (legal, for training purposes only). I have an interface that plugs
    |> into a cassette recorder and that works fine on the cassette. I have
    |> tried this same interface plugged into my computer, either line-in or
    |> the microphone jack, but when I record I get a loud hum noise and I
    |> can faintly hear myself in the background, though I have to talk or
    |> whistle loudly to do so. Apparantly I need a different interface. I
    |> have found them for sale for around $50, but I would prefer to make my
    |> on, usually these interfaces use fairly simply filter circuits. Any
    |> suggestions?
    |>
    |> Thanks
    |
    |
    |How about this?
    |
    |http://www.modemspy.com/en/index.php


    That appears to be software only. You still need a physical hardware
    interface.

    You might start some reading here

    http://www.solorb.com/elect/phone/tap/
    http://www.hut.fi/Misc/Electronics/circuits/teleinterface.html
    http://www.qsl.net/yo5ofh/hobby circuits/telephone_circuits.htm

    there's heaps more but mostly similar to these.
     
  8. Jay

    Jay Guest

    Okay, thanks for the advice. Apparently the mike jack isn't
    compatible with a telephone/cassette interface. What about the line
    in jack on the back of the computer? Would this be compatible with
    this type of interface?
     
  9. Dbowey

    Dbowey Guest

    Ischultz posted:

    << I am trying to find a way to record telephone conversations to my PC,
    (legal, for training purposes only). I have an interface that plugs
    into a cassette recorder and that works fine on the cassette. I have
    tried this same interface plugged into my computer, either line-in or
    the microphone jack, but when I record I get a loud hum noise and I
    can faintly hear myself in the background, though I have to talk or
    whistle loudly to do so. Apparantly I need a different interface. I
    have found them for sale for around $50, but I would prefer to make my
    on, usually these interfaces use fairly simply filter circuits. Any
    suggestions?
    The simple answer is that you must use a transformer.

    Your telephone line is a "balanced" line. Your sound card has an "unbalanced"
    input. When you connect between the telephone and the PC's line input using
    your interface (device) you are essentially placing a ground on one side of the
    telephone line, unbalancing it and causing it to be a great noise and hum
    receptor.

    The interface (device) you now have works with the cassette recorder because
    the interconnecting cable is short and the cassette recorder is not grounded.
    If it *were* grounded, it would cause noise and hummmmm too.

    You cannot fix this by using more capacitors anywhere. You must use a
    transformer.

    Tell us more about your interface device and we can help with specific details
    of the transformer you need.

    Don
     
  10. Aidan Grey

    Aidan Grey Guest


    I think some "voicemodems" allowed voice recordings to be played
    on a telephone line. There may be a model that will do exactly
    what you want.


    Aidan Grey
     
  11. jakdedert

    jakdedert Guest

    Actually that's all under software (ATAPI standard) control. IOW, with the
    proper program, *all* voice modems....

    jak
     
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