Microphone Pre-Amplifier explanation
And why the signal from microphone is so weak?


The microphone picks up air vibrations and the energy hitting it is proportional to the surface area of the microphone's moving element - consider a loud speaker a couple of metres away pumping out one watt - how much power/energy does the microphone diaphragm receive - Imagine how many microphones you can fit side by side at a couple of metres from this speaker in all directions.

How many would that be? Let me guess at ten thousand and, each one receives one ten-thousandth of one watt - that's a tenth of a milliwatt each. 600 ohm is normal for microphones so the signal amplitude (with a bit of handwaving and magic) is \$\sqrt{0.1 mW\times 600}\$ = 245 mV

Just how big did you expect a microphone signal to be?

The circuit is wrong as pointed out by others - it doesn't work.