Circuit Mono Preamp Mic BC108
The microphone preamp based
transistor described here is powered by 9 V and less than 1 mA current consumption, it will allows you to use a small 9 V rectangular conventional battery for several hours.
The -3 dB bandwidth is 30 Hz to 100 kHz. With the above scheme, the gain is about 35 dB to 40 dB (40 dB = amplification by a factor of 100).
It is designed for a dynamic microphone which output impedance is between 50 and 200 ohms. It is possible to connect a microphone which the output impedance is higher, but at the cost of a slight decrease in gain. Use with an electret microphone will be discussed in other article.