I have a condenser microphone that has no any model name or number. As we know condenser microphones need a bias voltage for operation. Some microphones need \$2 V\$[1]. and some need more. As we can not feed microphone more than its \$V_{max}\$, is there any way and measuring method to calculate the appropriate bias voltage of it without having its datasheet?

What is the appropriate Resistor to build the biasing voltage?


simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ The website that gave you the information has an area where you can make comments - it's right at the bottom of the page - did you make a comment - this seems a more appropriate "first" action. Also that site said check the data sheets to see what your microphone needs and as they cost less than half a pint of beer I'd have thought buying a new one or, maybe just feeding it via a 2k2 resistor from 5V and seeing what happens would also be a reasonable course of action. You won't need R2 - likely it's got a JFET inside that'll work from 2V to 10V with a resistor (R1) in the range of 1k to 10k \$\endgroup\$
    – Andy aka
    Commented Dec 24, 2013 at 21:17
  • \$\begingroup\$ Dear Andy aka, This means I should have seeing eyes, I didn't think about commenting on the website; Although the comment system is loading from google and google banned my region and could not be loaded. \$\endgroup\$ Commented Dec 24, 2013 at 21:28
  • \$\begingroup\$ Wow, what region was that if it's not too rude to ask? Regards resistor see my first comment. \$\endgroup\$
    – Andy aka
    Commented Dec 24, 2013 at 21:54
  • \$\begingroup\$ @Andyaka: My region is Iran (Persia) :) \$\endgroup\$ Commented Dec 24, 2013 at 22:15
  • \$\begingroup\$ So presumably google (search engine) cannot be used in Iran. I'm old enough to rememberber the old Shah of Iran!!! Died of cancer I believe after the revolution in 77? Well, that's the story we got over here. \$\endgroup\$
    – Andy aka
    Commented Dec 24, 2013 at 22:27

1 Answer 1


There is really no way to non-destructively determine the maximum bias voltage the mic can take. If it really is a condenser mic, not electret (which are driven similarly), then up to 10 V is almost certainly safe. 2 V is safe for just about any kind of mic that requires a bias voltage. You can start there and see what it sounds like. If the signal is too weak and buried in noise, crank up the bias voltage.

Look around for similar-looking models and see what bias voltages they require. Some old condenser mics used up to 100 V back in the tube days. Less voltage doesn't hurt the mic, but you get lower signal to noise ratio. Too high a voltage and something will arc, probably causing permanent damage.

  • \$\begingroup\$ Express thanks for excellent answer, Would you mind also answer to my new edited question about appropriate needed resistor? And How should we calculate it? \$\endgroup\$ Commented Dec 24, 2013 at 21:30
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    \$\begingroup\$ @Moha: The resistor needs to be large enough to not load the microphone output significantly. Try 10 kOhms if you have no other information. \$\endgroup\$ Commented Dec 24, 2013 at 22:00

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