using a small unknown mic

[large_ghostman]

I have a couple of very small mics I would like to use, no idea of make etc, no markings. 1 red and 1 black wire and looks like this

does it need any kind of driving circuit? or do I just hook it upto some sort of amplifier? so far no luck in getting any sound out, but I only tried to plug into laptop, I might try and scope it see what it puts out, in a ideal world a nice simple 2 stage transistor amp would be great. I dont want to use amplifier chip if I can help it.
Any idea's?

 

[audioguru]

It looks like an Electret Mic that is used in many products today. It is a "condenser mic" that has a diaphragm vibrated by sounds inside the field of a high voltage so its output is a very high impedance capacitive voltage divider. An old condenser mic used an external 48V power supply or battery to provide the high voltage. An electret mic has the high voltage permanently charged in its electret material. Since the impedance is very high then it has a Jfet impedance converter built-in.

The Jfet needs a few volts at 0.5mA so connect a 10k resistor to its red wire and the other end to +9V (or 4.7k to +5V). Connect the black wire (which should be seen and measured connected to its metal case) to 0V. The red wire output is connected through a coupling capacitor to the input of a preamp and will be about only 10mV when you speak normally about 10cm away. A laptop mic input has the resistor that powers an electret mic built-in.


Some electret mics have 3 wires. Then the Jfet is a source-follower output and the other two wires are the positive 9V or 5V supply and 0V.

 

[audioguru]

Deleted a double post.

 

[4pyros]

Here you go;
https://en.wikipedia.org/wiki/Electret_microphone

 

[large_ghostman]

Thanks guys!! exactly the info I was looking for! Thanks AG and 4pyros, now I know how to get it going , it's only for a experiment with one my cubes.
I will post pics when its done!