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Electret wiring

Electret personal microphones are all unbalanced. They all need a screen, both for the cable and for the grille and casing around the capsule. This usually gets connected to 0V. The electronics inside the capsule will have two external connections. One connection always needs to be kept more +ve than the other but it makes no difference if the higher one is fixed at, say, +5V and the lower one wiggles, or the lower one is fixed at 0V and the higher one wiggles. Both will produce the same (unbalanced) audio signal.

The wiring is simple enough for the following “trial and error” method to be employed while listening to the microphones output. Assuming you have a screened cable with one or two cores and a stereo 3.5 mm plug:

#Connect the microphone cable screen to the sleeve of the plug.
#Connect one of the cores (or the only one) to the tip and ring.

The microphone will probably work, if it doesn’t, try the other core to tip and ring.
#Connect any spare core to the sleeve.

If the mic doesn’t work with either core connected to tip & ring it is probably a negative biased type (some Tram TR50s, ECM 55s and 77s). These can be made to function by swapping the screen and core connections but there is more risk of hum and interference with this arrangement.

The chances are that by now the microphone will be working. The voltages in use make this procedure quite safe for both you and the microphone. Plug-in Power is usually a slightly lower voltage than that from radio microphone transmitters or phantom adaptors, so you should expect a slightly reduced maximum SPL for the microphone.

This powering arrangement is electrically very similar to Plug-in Power so virtually any electret microphone in the recordist’s bag can be used with a Plug-in Power input.

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