Actually, not only of the amplifier.
The diagrambelow allows you to automatically disconnect from the network any sound-reproducing device in the absence of the output thereof sound for some time.

Automatic shutdown of the amplifier

The circuit is powered by the internal power supply of the device. Button S1 is turned on. Charging the two capacitors, transistors are opened and the relays and their contacts locks the button, leaving, therefore, the device is in an enabled state.
Further, the audio signal is the output signal of the amplifier or whatever you have is input to the transistor VT1 and it cannot be closed.
In the absence of a signal at the output, the capacitors are discharged, the transistors are closed and the relay de-energizes the load.
Temporary switch-off delay depends on the capacitance of the capacitors C1 and C2 and resistor R3. More than all this, the longer it will remain on the device in the absence of any signs of life at the output.

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