power distribution and electret microphones (voltage dividers and voltage regulators)

Thread Starter

BobbyTheD

Joined Mar 10, 2016
34
hi-
i recently got some electret elements that are spec'd for 3v. i've been using a 9v with a voltage divider and it seems to be working ok, but i'd like to get a better sense of what's going on. am i wasting a lot of power with something like that? will it drain the battery quickly? would a voltage regulator waste less power? if so, how much? do voltage dividers or voltage regulators make any impact on the audio quality of the microphone?
 

Audioguru again

Joined Oct 21, 2019
3,632
Please post the datasheet for your electret mic to see its specs. If it has no datasheet then look at the datasheets of a few of the hundreds of electret mics at digikey.com.

Most electret microphones have a typical operating voltage of 3V but a maximum allowed operating voltage of 10V, the typical current draw is 0.35mA.
Then with a 9V supply filtered with a series 1k and a 47uF capacitor to ground, a series resistor feeding the mic will be (9V - 3V)/0.35mA= 17k ohms minus the 1k ohms. I always use a 10k resistor in series with a 1k filtering resistor when the supply is a 9V battery so that the mic still works when the battery has dropped to 5V.

The electret mic has a Jfet in it that forms a voltage divider with the series resistor that powers it so adding your own voltage divider kills the output level from the mic and also kills the battery.

If you connect a 3V battery to an electret mic then the very low resistance of the battery will kill the output signal. Each mic needs to have its own series 10k resistor.
 

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LowQCab

Joined Nov 6, 2012
1,183
The "10K" Resistor is not a magic number.
What You should be going for is half of the Battery-Voltage across the Resistor, and
therefore, also, half of the Battery-Voltage across the Mic-Element.
This creates a 50% Bias at the Mic Output, and
provides the maximum, non-distorted, Output capability.

Since the Load on the Output of the Mic is so low, (100K),
huge Bulk-Storage-Electrolytic-Capacitors offer no advantages,
a single 1uf Ceramic-Cap will do everything needed,
and provide a much lower High-Frequency-Impedance.
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