creating a pre-amp for electret mic.

[zagga20]

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.

 

[ben7]

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

Is that what you are looking for?

 

[dougy83]

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.

 

[zagga20]

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?

 

[dougy83]

yep.

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

 

[Torben]

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.

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

 

[dougy83]

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

 

[audioguru]

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.