Modulation with clean audio is always welcome, so, for those who use a gain microphone, I leave the following diagram, I used it for a long time, it is very useful. Can use microphone (Dynamic or Electret).
This project has a very good gain, with 100 mV (millivolts) of Input signal amplitude, we get approximately 532 mV at 1.22 Volts of Output signal.
Short circuit for electret microphone. To use Dynamic Microphone remove 10K resistor and 100nF capacitor.
