NE555 based Microphone amplifier
IC NE555 or commonly known as 555 is an IC that is well known among electronics practitioners as an IC for timers, and can be used to form monostable or bistable multivibrator circuits. But not many know that the 555 IC can also be used as an audio signal amplifier. By utilizing the ability of IC 555 as a monostable multivibrator to generate PWM (pulse width modulation) pulses.
The audio signal comes from the microphone, then is amplified with 1 transistor amplifier, used to trigger IC 555. The pulse width will be determined by the incoming audio signal level. An incoming signal with a low level will produce a narrow pulse, while an incoming signal with a higher level will produce a wide pulse. The output signal from the 555 is of practically constant amplitude, but variable pulse width. It is fed to the speakers, and the resulting sound is similar to that produced by a typical audio amplifier.