# Where can I find electrical pinout of C152 microphone jack and DC bias?

Would anyone have the pinout and/or specs of the C152 passenger/pilot microphone jack? I'd also like to know what DC bias voltage, if any, the plane provides to the microphone.

Here's what I have so far, which may or may not be accurate:

              Headphone side     Plane Side
Sleeve             GND              GND
Ring         MIC OUT/BIAS IN       ???(?V)
Tip              UNUSED?            PTT?


I've dug through some Bendix/King nav/com radio manuals, but they don't tell you about what to expect on the plane side of things.

Thanks!

There are some great resources on webpages mostly aimed at home builders and experimental aviation enthusiasts as well as some electrical engineering forums.

Most of these aviation radios are set-up for use with a carbon microphone. They are fairly simple pieces of kit. If my memory serves me correctly the acceptable forward bias voltage range is set by the RTCA (https://www.rtca.org/) however I can't find a solid reference for this.

As far as I know, so called "GA plugs" (The 5.25mm/6.35mm style plugs) are wired as follows:

Sleeve             GND                           GND
Ring         MIC OUT/BIAS IN                    8-16v (Short circuit current ~150ma)
Tip       PTT  (Switch shorts to GND)            PTT


The reasoning behind the PTT switch still being assigned is for handheld backup microphones. Many newer headsets don't use carbon microphones and use the electret capsule style microphones instead and therefore require some complex electrical engineering wizardry to drive.