In this project, the output from the microphone (mic) is fed to the base of Transistor T1 (BC 547) which acts as a class B amplifier. When the input signal increases towards positive peak, the base of T1 gets more and more forward bias. At the same time the collector current also increases. Due to this the voltage drop across resistor R1 (1k) rises and consequently the output goes on decreasing. When the signal drops towards the negative peak, the forward bias on the base of T1 goes on falling along with the collector current. Hence the voltage drop across the resistor R1 also falls and the output also goes on increasing. Also note that the output is 180 out of phase with respect to the input, i.e., when the input increases the output decreases and vice versa. The Resistor R2 is used to check the base current of T1.
Filed Under: Electronic Projects