Electret question

Discussion in 'The Projects Forum' started by TestTones, Mar 8, 2012.

  1. TestTones

    Thread Starter New Member

    Sep 24, 2011
    What is the relevance of capacitor values placed directly on the + lead of an electret?

    From what I gather, it serves as a power capacitor similar to that in an amplifier? I have used two different values. The higher Farad and voltage cap gave me greater output. I suppose this is irrelevant considering my second preamp stage it feeds but I would like to understand this device better.

    And somewhat unrelated.
    Would we consider these IC's?
    It is an integrated circuit as I understand it since it is a collection of specific devices consolidated.
  2. bertus


    Apr 5, 2008

    Can you post the related schematic?
    Then we can see what you are talking about.

  3. TestTones

    Thread Starter New Member

    Sep 24, 2011
    This is more or less the same base circuit

    The 1uF cap.
    My circuit is far more extensive but I first used a 10uF then found greater output by using a 50v 33uF in my second build..I must have 60 or 70 of them bought off EBay for just a few bucks last year. Maybe I finally found something to use them for!
  4. Audioguru

    New Member

    Dec 20, 2007
    The preamp circuit should have a fairly high input impedance to avoid loading down the mic. It should be at least 25k ohms.
    The resistor powering the mic should be 10k ohms for a higher output level.

    Then you can calculate the value of the coupling capacitor. The mic and 10k resistor total about 2.5k plus the 25k input impedance of the preamp equals 27.5k ohms. For a -3dB cutoff frequency of 50Hz then the value of the coupling capacitor should be 0.125uF but a 0.15uF capacitor is fine.

    Since you used a 33uF capacitor then the load for your mic was probably 110 ohms or less which is like a dead short to the poor little mic.