Using signal from tone board to trigger a relay to turn amp on

I am wanting to work out a way of turning on my amp when signal starts as my amp uses quite a lot of pwoer at idle. There are circuits which use op amps etc but I was hoping to keep it simple. Is there anything I can use from the header which will allow me to swtich a relay when the signal starts? I don’t want to put anything directly in the signal path if I can avoid it. The only risk to such a simple approach that I can see is that it might need some tweaking so that the DAC doesn’t trigger the relay at idle. I notice that my amps power usage goes down at idle when the inputs (DAC outputs) are unplugged, so even though it is supposed to be a very quiet DAC, it must be sending something to the amp even when no music is playing.