capacitor choice for mic power

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TheGuy

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I'm just making a quick mic power circuit, following the design that's attached. However, I don't have a 1uF capacitor at hand, and I need to get this thing done quickly. Will using a 2.2uF, or 0.47uF, capacitor make much difference, and what will the effects be? I'm a total electronics newbie, so I have no idea.

Thanks in advance for any input.
 

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The value of the capacitors affects the low frequency response. But you must use the load resistance in the calculation.
Maybe use a 50Hz cutoff frequency (where the output level is reduced to 0.707 times or -3dB) so that male voices sound realistic.

You don't know the DC voltages so non-polar capacitors (film type) should be used.
 
Ohh, right, I get it now (I think).

So technically, I don't need a capacitor at all? I'll just have the full frequency response then.
 
TheGuy said:
So technically, I don't need a capacitor at all? I'll just have the full frequency response then.
Click to expand...
The capacitor is needed to isolate the different DC voltage on the mic from the DC voltage on whatever it feeds.
 
You need to pass the AC signal and block the DC. A diode would rectify the audio which produces severe distortion.
 
Last edited:
I don't understand I'm afraid.

I didn't think this circuit would have any AC current in it, as the power is coming from a 9v battery, and the output of the mic is going to go into a camcorder.
 
Audio is an AC signal. The DC voltage at the output of the electret mic is anywhere from +1V to +8V. The audio causes it to increase and decrease 0.01V so the AC signal is 0.02V peak to peak. This level is very low so the camcorder must have a preamp to amplify it to a useable level. Then why doesn't it already have a jack for an electret mic and a resistor to power the mic and a coupling capacitor??

You cannot calculate the value for the coupling capacitors unless you know what is the input resistance of the preamp.
 
audioguru said:
Then why doesn't it already have a jack for an electret mic and a resistor to power the mic and a coupling capacitor??
Click to expand...

Well, the camcorder has a jack input and a preamp, but does not supply power to the capsule, so I'm throwing this together so that I can use any electret with it. I'm going to try the circuit with a 2.2uF capacitor, and see if it works. I'm pretty sure that it won't damage the camcorder, as it's had far worse things going into it.
 
2.2uF will be fine, if it's polarised then connect the +ve to the mike side.

However, you appear to be showing a circuit for a balanced condensor mike, and not for an electret one.
 
His circuit might be for a stereo electret mic to record a person who has two mouths.
 
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