audio input for VU meter

[shinigami.alv]

I have a VU meter circuit as above with a condenser mic which i bought online **broken link removed** and is wondering how can i apply the output of the mic to the audio input of LM3915? do i simply amplify the mic output then connect to the circuit?

 

[BradtheRad]

A condenser mic may produce a strong enough signal to drive the 3915 without being amplified. I'm not sure if you can do this with as low as 1.5V supply to the mic. But if you use several volts then you may get several led's to light at normal speech loudness.

The 3915 will ignore the negative waveforms, and respond to the positive.

If you find the mic signal is too soft, then you can amplify it using a single transistor.

The idle level must be zero V, because no led should light when there is no signal. Hence you might use a PNP type to accomplish this (if you can figure out the right way to bias it referenced to the positive supply, etc.).

Or configure an NPN as in the schematic below.