Audio Preamp – Designing a Circuit with Falstad.com

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.

Two things pop out:

1. You don't have a capacitor across each battery. This is likely the problem. Put something like a 470 µF 16 V cap across each power feed where it enters the board.

   I'm guessing that you are getting feedback via the power feed. This was reinforced when you mentioned that adding bypass caps made it better, but didn't solve the problem. The batteries have too much impedance at audio frequencies, so a little change in current draw in one section can make a signal in another. The caps across the batteries are to decrease the impedance of the power supply

2. Electrolytic caps are unsuitable here. All your signals are centered around 0V. There is no average bias on any of the caps, so the signals across them will be both positive and negative. That's bad for electrolytics, and bad for the signal since electrolytics don't have symmetric electrical properties between positive and negative voltages applied to them.

There may also be issues particular to the opamp, but without a link to the datasheet I can't tell. No, I'm not going to chase down the datasheet to answer your question. It's your job to do that and then give us a link to it.