Microphone compatibility

VE3GRG

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

KD0RC

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

7.20 MICROPHONE JACK

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

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

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

Thank you for the information. It should help in solving the problem.

VE3GRG

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.

SmittyHalibut

Resurrect a very old thread: Aren't aviation headsets usually Carbon mic elements, not Electret? I think the Carbon mics require a higher bias voltage than Electrets.

KD0RC

I'm no expert, but I don't think aviation headsets have used carbon button elements in a very long time. I think you can get them in electret or dynamic these days.

VE3GRG

You pretty much hit the nail on the head . The only things I can add are 1. The military seems to use dynamic which are extremely low impedance and produce very little voltage. 2. Most private avionics are using electret which use about three times the excitation voltage available from a Flex radio. 3. My solution to the problem was to buy a Heil HC-7 element which adapts well to the David Clark headset. The audio response curve which seems to suit this element with the sock installed favours the high end from 1khz to 4 khz. I have the low limit set to 100 Hz and the high limit set to 3500 Hz. Another op could probably spend more time and obtain a better result but I tend to operate more cw so the audio is less important to me. Finally thank you to those who have taken the time to extend themselves in answering the query.