pre amp help needed

[Neil Groves]

Hi Guys, well i just got around to finishing my colour organ and all is now fine when i apply a line level signal, i now wish to add a pre amp at the front end so i can select either mic or line to drive the circuit, i don't know much about pre amps in terms of input/output voltages but i am assuming with a mic insert, i am dealing with a few micro volts? i need to raise this to a couple hundred millivolts using an op amp since i have one half of a dual op amp unused on my board, i can't seem to find a circuit online surprisingly, could someone point me in the right direction please?

Neil.

 

[audioguru]

A microphone has an output of about 10mV when it is about 10cm in front of your mouth and you are talking in a normal conversation level.
Then the preamp needs a gain of about 200 so that a volume control can adjust its level up or down.

Use a low noise audio opamp for the preamp.

 

[Mosaic]

https://www.minidisc.org/mic_preamp/Simple Stereo Electret Mic Preamp.htm

 

[audioguru]

https://www.minidisc.org/mic_preamp/Simple Stereo Electret Mic Preamp.htm

The website does not work anymore.

 

[Mosaic]

Yes it works fine.

 

[Mosaic]

Here is the circuit image from the website....sans all the explanations about its operation.

 

[audioguru]

I made comments on the schematic.

 

[Neil Groves]

ok thanks guys, a project for the weekend me thinks.

Neil.

 

[audioguru]

An entire weekend?
2 minutes to design the circuit and maybe 5 minutes to build it.
Then 2 minutes to get the generator and 'scope warmed up.
The actual test takes a few seconds.

Drink wine or beer for the remainder of the weekend.

 

[Neil Groves]

lol....your forgetting you are way more experienced than me, i try to take my time and learn something along the way.

thanks Audioguru.

Neil.