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Microphone compatibility

Does anyone have experience using the David Clark M-7A microphone with a Flex 6400?

Best Answer

  • KD0RC
    KD0RC Broomfield, COMember, Super Elmer Moderator
    Answer ✓

    @VE3GRG , Here is the info from the Flex 6400 and 6600 Hardware Manual:


    The MIC connector accepts a 1/8-inch (3.5mm) stereo (TRS) plug and provides a pseudo-balanced microphone input. Pseudo-balanced means that the mic (+) and mic (-) lines are balanced all the way to the input of the A/D converter, where the mic (-) line is DC grounded. The connector may be used with dynamic or electret microphone elements. A software enabled 3V bias voltage through a 2.1k Ohm source impedance may be applied to the Mic (+) line for electret microphones.


  • VE7ATJ_Don
    VE7ATJ_Don British ColumbiaMember ✭✭✭

    Hi... I'd suggest you take a look at this recent discussion re: aviation headsets use with Flex:

    Aviation Headsets - any use? — FlexRadio Community

  • VE3GRG
    VE3GRG Member
    Thank you for referring me to this post. The DC 10-76 headset with the dynamic microphone works fine and the great thing is that none of the DC headsets have sensitive electronics which are subject to rf interference making these headsets desirable. They are also quiet for listening another desirable feature. DC headsets also make use of a condenser microphone. The condenser Mic requires a bias excitation which is available from the Flex radios but how much is the question. After establishing the bias it now becomes desirable to find which microphone to select from the software menu and this is what I was asking if anyone had experience with. The answer to this appears to be that no one has done any research with this combination and there is also a lack of technical info available about what is supplied by the Flex radio in the way of bias and in impedance values. Interfacing the operator to the radio is sometimes a problem.
  • VE3GRG
    VE3GRG Member
    Thank you for the information. It should help in solving the problem.
  • VE3GRG
    VE3GRG Member
    The answer is quite simple. The M7A requires between 9 and 28 volts DC for excitation. The 3 Volts supplied by Flex is not enough. Pity as the DC headsets are excellent quality.