Connecting Electret to Dynamic Input

[turbodude]

Hi guys, I have searched for a couple of hours on the forum but not found anything. I am wanting to connect an Electret mic to a unit that usually has a dynamic mic connected. The dynamic mic that is usually connected(came with teh unit) has an output impedance of 500 ohms. I am wanting to connect an electret that has 1kohm impedance and run it from 1.5v battery. I know the standard way of using an electret where there is a resistor supplying the electret from the battery (calculated value required for 0.5mA is 3kohm). If I have a 1uF electrolytic between the mic+ and the output of the mic circuit how do I work out what the output impedance of the circuit is (I assume the cap and the electret itself affect this). Secondly how do I make it about 500ohms?

Thanks in advance

[sreten]

Hi,

I've never seen a decent electret that can drive 600 ohms directly,
they drive ~ 47kohms and use a transformer to drive 600 ohms,
either an internal transformer in the microphone or external.
All the 1.5V micrphones I've seen have a 600 ohm transformer.

There is a way of connecting electrets to PC sounds cards without
the transformer and using a ~ 2.2K resistor, but noise is poor.

/sreten.

[clem_o]

The output Z would be roughly the source resistor value - 1.5K... either you stick in an active amplifier to drop the impedance (i.e. an op-amp) or, use a transformer.

Cheers