This circuit follows will connects the speakers to the power amplifier output only a few seconds after the amplifier is powered ON, so that the speakers do not accept popped up by a high voltage and you would not Hear a loud thud sound from the speakers When the amplifier is switched on. This stuff is very harmful to the speakers.
When the amplifier is powered on the bridge D1 also gets powered through the amplifier’s power switch. Capacitor C1 filters the output of bridge rectifier D1. When the power switch is made ON, the transistor Q1 gets switched ON only after the capacitor C2 is sufficiently charged (0.7V) through the resistor R1. Here the value of C2 and R1 are so selected that the time delay is around 2 seconds. So the relay gets activated only after a few seconds the amplifier is powered ON and until that time the speaker will be kept isolated from the amplifier’s audio output as the speaker is connected to the amplifier’s output through the N/O contact of the relay. During this initial delay period the output of amplifier will be grounded by the resistor R2 through the N/C contact of the relay. This is done in order to ensure that the DC blocking capacitor at the amplifier’s output is charged before it is connected to the speaker.
Better quality speaker protector Circuit