Need help interfacing radio shack phone recorder into mixing board

Discussion in 'DIY Discussion' started by yegg57, Aug 28, 2021.

  1. yegg57

    yegg57

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    DuoFone 43-2638 (Radio Shack) telephone recording controller
    This device has a standard modular jack to plug into the telephone line.
    There is also a 1/8" (3.5mm) plug for either the microphone jack or the
    earphone jack of an old style cassette recorders. There is also a 1/16" plug
    that would have controlled the motor, but I have no use for that as I am simply
    interested in using the audio as an input to my mixer.

    I have been experimenting with attaching the tip/ring wires of the 1/8" jack to attempt
    to use this as an input either into a 1/4" line or XLR mic connector on a mixing board
    that I've had for awhile, but I am always getting an annoying hum no matter what pins I hook it up to.

    I've forgotten more electronics than I remember from 50 years ago in school and am wondering
    if anyone knows if I need to install a capacitor or a resistor either in series or parallel
    to make the buzzing go away and just sound normal.

    Before anyone "goes off" about wiretapping laws this would be used as likely the 2nd line
    for a podcast. I already have TRRS cable to go into my cell phone and have that portion
    working wonderfully.

    Any help will be greatly appreciated.
     
    yegg57, Aug 28, 2021
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  2. yegg57

    Sergeauckland

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    I'm trying to find a user manual for the 43-2638 item so I can understand how it's supposed to work. Telephone lines are balanced, but cassette recorder inputs are unbalanced, so there must be some conversion going on in the unit.

    In theory, you should be able to connect the telephone line to XLR pins 2 & 3 and be able to record/hear both sides of a conversation. It may be safer to put some capacitors in series with the XLR pins as there may be 50v DC between the two line wires and ground depending on the telephone system. The signal level will be around the 0dBu level so the XLR input should be a line level input, or if at mic level with the gain turned down.

    S.
     
    Sergeauckland, Aug 29, 2021
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