When you switch on your amplifier, you can see your speaker pop up with high power, and it can be harmful to your speaker. To make your speaker’s life time last longer, you have to avoid such situation. You can use an electronic circuit to protect your speaker, that connect your speaker to your power amplifier 1-2 second after the amplifier is powered. Your circuit has to disconnect the speaker as soon as possible after you press the power-off switch, before the capacitor loose their charges and cause instability in the power amplifier’s output and harm your speaker. The schematic diagram of this circuit is shown below.
The circuit is designed for 12 volts amplifier with DC decoupling capacitor on its output. When the power supply is turned on, the relay need few seconds to be active since C4 is slowly charged by current flow through R2. When the amplifier is turned off, the relay will immediately turned off because the supply come from a small capacitor C2, no time to wait the large capacitor on amplifier’s main supply begin loosing its charge. The resistor R3 (120 Ohm 2Watt) is needed to make sure that the DC blocking capacitor is first charged before connected to the speaker.