i failed to open the case... it's radioshack's race-scanner's headset...
well, I found only two pin went in to the mic... like david clark. impedance is somewhere 250ohm.
the mic pin and v+ is shorted... I tested with meter. (in headset, i have though pins for v+ and mic out, both found shorted internally).
yes!! distorted when with the amp. without the amp, volume is too too too low. but when I blow, i get the sound... but when i talk, others barely hear me...
Mishu~