The kit 555 amplifier 555 can be used as an amplifier. In the kit 555 amplifiers the first block is power supply in the input is 230V AC which is step down using the transformer (12-0-12) .The 12V ac input is fed to the bridge diode to gives 12V pulsating DC. This DC voltage is filtered through the capacitor to remove the ripples. The filtered DC is fed to 7812 regulator to fetch +12v regulated output.
The kit 555 amplifier in the normal mode, we just open circuit the 5th pin (Control voltage pin) of 555 IC. But the most interesting fact we often neglect is that if a low frequency signal is applied to the 5th pin of 555 IC, pulse width modulation starts. Here the oscillating frequency of 555 astable is approximately 145 KHz. The discharge time of capacitor via diode 1N4007 is too fast since there is no resistor to discharge. The condenser MIC is used as transducer to sense the incoming audio signals and convert them to proper electrical signals. The output of the MIC is then fed to the transistor via a capacitor. This capacitor is used to remove the DC component of the signal. Resistor provides the necessary biasing to the condenser microphone. And the resistors R2 and R3 give potential divider bias to BC547 transistor. The capacitor C2 and resistor R4 provides negative feedback to the transistor circuit which is essential for amplification. The pre amplified audio signal is fed to the control voltage pin of 555 timer astable multivibrator running with 145kHz.The process of pulse width modulation starts and as we know the speaker does not respond to this much high frequency, it responses to the usual DC value of the modulated output. Hence the audio signal gets amplified.