Yes, the third transistor provides the gain. Scrooge's has a "charge pump" - see the diode on the base of the second transistor? Imagine that's one valve, and the base-emitter junction is another, and C2 is a cylinder that moves back and forth - works like a pump.
I simply copied your first posted preamp circuit.
Its output level is low because the input impedance of the transistor is so low that it loads down (attenuates) the medium output impedance level from the microphone.
My second transistor is a high input impedance half-wave rectifier. When the signal at its base goes positive (C2 charges) then it conducts and makes its emitter go positive and charge the filter capacitor.
The diode discharges C2 when the signal goes negative.
If the diode is missing then C2 keeps charging each half-cycle then it does not turn on the second transistor anymore.
ok thx but if i will put a potetiometer where is what is the best resistor to replace it ?
and one more question it should be red ??? lol
and can i put 4 LEDs insted of 1 in the circuit or it will affect the performance?
The LEDs are fairly bright when their current is 20mA.
160k ohms in series with 3 red LEDs and a 9V supply results in a current of only 22.5uA so the LEDs will be extremely dim.
160 ohms in series with 3 red LEDs and a 9V supply results in a current of 22mA so the LEDs will be fairly bright.
If I write 160 then it is 160 ohms. If I write 160k then it is 160k ohms.