Convert SMC Mic Amp to Audio Oscillator

Convert SMT Mic Amp to Audio Oscillator

Hi

I have the circuit below on a tiny SMT factory built wireless Mic PCB, and I would like to replace the mic with a tiny SMC audio oscillator that produces a constant tone.



Note I have used the transistor symbol as shown, but I can not confirm which pin is which or NPN/PNP of the transistor on the board.

Ideally I would like to modify the existing circuit board, using the existing mic amp SMC transistor as a single transistor oscillator, but I don't know how I would go about that circuit wise - any suggestions?

Failing I could add another small pcb with a tone generator circuit on, outputting at mic levels into the existing mic connections (and removing the bias resistor). any ideas smaller / simpler than an SMC 555?

Thanks
Kev

You can build a simple RC oscillator:

Thanks, I have the oscillator working on breadboard, but now I need to get the output at the right level.

The output of the transistor in the original circuit is 0.2v peak to peak, around a dc bias of around 2.75 volts.

How do I get the oscillator output down to that level and at the right bias using the minimum number of components?

Thanks
Kevin

The oscillator amplitude is effectively stabilized at the amplifier's clipping level. It's not easy to set a lower level. The most simple way to attenuate the output level is to use a two resistor voltage divider in place of R1.