The circuit was designed to provide more efficient output with a dynamic microphone by using a low noise preamplifier.
As the dynamic microphone produces 200 to 600 ohm output impedance, it consists of discrete amplifier that runs on 3 stage of amplification with gain control. The gain is a measure of the ability of a circuit or an amplifier to increase the power or amplitude of a signal, usually defined as the mean ratio of the signal output of a system to the signal input of the same system. The transistors utilized was BC547 with 150ºC junction temperature and through hole package, but other types of transistors may also be used. With the first stage functioning on Q1 via the common base configuration, the transistor enhances the overall signal to noise ratio and conducts at low noise levels. While a direct coupled amplifier comprises of Q2 and Q3. The circuits gain is reduced to zero by the 47K ohm preset resistor.
The roll off frequency provided by the circuit is at 30 Hz while the frequency response is at 100 KHz. Roll off is defined as the Gradually increasing loss or attenuation with increase or decrease of frequency beyond the substantially flat portion of the amplitude-frequency response characteristic of a system or transducer. The first stage on Q1 has a gain of around 4.7 from the ratio of Rc & Re but will be reduced when supplying into the impedance of Q2 and Q3 with a shunt resistor. The amplifier gain from Q2 and Q3 is based on the ratio of Rc & Re while Q3 conducts on as emitter follower. As 12 V is supplied to the base voltage, the collector current of Q1 is 200 uA during the first stage
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