Different electret microphones in headsets

Discussion in 'General Electronics Chat' started by jaydnul, Jul 27, 2015.

  1. jaydnul

    Thread Starter Member

    Apr 2, 2015

    I have two pairs of headsets here and only one works with my PC (the microphone that is). They are both the same pin out, ground is the ring and mic hot is the sleeve.

    Without plugging them in, the pair that work with my PC mic in jack have a DC resistance of 1.4K while the other pair (which were made to work with Apple devices) is at 4M. I have a few questions.

    Am I just measuring the resistance across the source and drain of the FET inside these microphone capsules? If so, why isn't the resistance much lower since the actual mic inside the capsule is biasing the FETs gate with a static charge?

    Also, why do both mics work with an apple product but the one that was designed for Apple products (4M) won't work with a normal PC mic jack. Is the supply voltage different?

    Is there a way to design a circuit that forces the apple designed mic to behave like the standard 1.4K mic without opening up the capsules?

  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Every one I have looked at is just the reverse of that. Sleeve is always the common(Gnd).

    Apple always has to be different so they can charge more for their overpriced crap.
  3. cornishlad


    Jul 31, 2013
    PC soundcards usually (AFAIK) have a 3.5mm jack socket with sleeve, tip and ring. The power is delivered via the ring I think. so PC compatable mics use a "stereo" type jack (sleeve, tip and ring)
    Don't know about Apple but sometimes power and audio are on the same pin on the mic side so such a mic will only have a "mono" type jack, ie tip and sleeve. Does this throw any light on your problem ?
  4. jaydnul

    Thread Starter Member

    Apr 2, 2015
    Since my PC was only outputting 1.7V at the mic pin, I took a shot in the dark and assumed the transistor was biased at a higher voltage and wasn't entering it's active stage. I hooked up a voltage source in series and gradually increased until it activated. My guess is the microphone has a bigger static charge difference, which is biasing the gate at a higher voltage, than the other microphone that worked.

    Anyways, problem solved. Thanks for the help!