creating a pre-amp for electret mic.

Hi guys this is my first post, so here it goes.


Im designing a Pre-amp for an electret mic, and ive been told that: "You should model the powered electret microphone as a DC source of around 5 V in series with an AC source of around 1 mV and a resistor of around 2.2 kΩ. This will then be coupled by a capacitor (whose value you need to choose, with appropriate justification) to your amplifier."

I was hoping that some of you may be able to help me clarify some of this.

What exactly is it meant by, coupling? I understand that the capacitor should be able to eliminate the DC component. But i am unsure on how to do this.

https://www.electro-tech-online.com/attachments/electret-mic-preamp2-png.28447/

Is that what you are looking for?

I think your lecturer is saying that the microphone may be modelled by the series connection of a 5V DC voltage source, 1mV AC voltage source and a 2k2 resistor. The (decoupling) capacitor is also connected in series with this to the input of your amplifier.

Oh ok, so for the cap to remove the dc component of te mic it should be in series with the resistor and the 2 sources and then imputed to the ore amp?

yep.

You said you have to justify the value for the cap - it depends on the frequencies you want to amplify.

dougy83 said:

I think your lecturer is saying that the microphone may be modelled by the series connection of a 5V DC voltage source, 1mV AC voltage source and a 2k2 resistor. The (decoupling) capacitor is also connected in series with this to the input of your amplifier.

Click to expand...

Just picking nits here, but my understanding is that you're describing a coupling capacitor. A decoupling (bypass) cap goes to ground to suppress AC/transients while a coupling capacitor is in series and blocks DC.

If I'm wrong I'm sure someone will be along presently to spank me.



Cheers,

Torben

quite right. maybe it is I that will be spanked.

The electret mic "represents" a 2.2k ohms generator. You do not add a 2.2k resistor. The 2.2k resistance is in parallel with the 10k resistor that powers thew mic so they combine to produce a signal source of 1.8k ohms.