Okay so here is my BA of hacker Electronics:

APRS and many have disassemble my famous VIVANCO EM216
as you say it trs trs light ...
The circuit PCB (probably "made in china" contains:
-2 Type electret capsules (the end of the cord)
Each via a polarized-R = 1.2K to VCC = 1.5V LR06 = voltage
(O indicates the impdance 1K)
Each audio-(+ the electret) through a capacity to 2.5f (to remove the comp. Continues) and go to the output (OUT Stereo)
-A switch ON / OFF SERIES with the good battery ... OK ...
A-MONO / STEREO switch that bypasses the two signals of two electrets
.... And to the MONO!
(Hence the impdance passing about 500 Ohms = 1.2 K / / 1.2K)

And I thought there was (peut-tre. .. yes, I know .... you can always RVer ...)
a small gain of 20dB prampli two transistors as the "microphone ARCHOS 100878"
... Well no ...
Fortunately, I did not pay for expensive ... phew OCCAZ 13 euros ...

in addition, After a few measures, it is not the top of electret microphones anyway ...

http://www.lagom.nl/misc/skytronic.html

So much for my own impressions and info
Bye
Stphane