Auto-switching Bluetooth Amplifier

In my front room, I have some big speakers and an amplifier connected to my TV. However sometimes, I don’t want the TV on, and don’t want the big clunky amplifier - I just want some background music, played off my phone, that I can turn on and control wirelessly.
That’s a problem - because the amplifier expects to be connected directly to the speakers. The only option would be to leave the amplifier on, or to somehow control mains voltages from signals on a small Bluetooth receiver.
In this instructable you’ll modify a SANWU Bluetooth Audio Amplifier so that it’ll control a set of 4 relays. Whenever the Bluetooth amplifier needs to play music, it’ll switch them over. When it doesn’t need to play anything (including when it’s connected via Bluetooth but no music is playing), the relays are in the default position which leaves the amplifier connected.
The relays are rated 10A at 250V, so should happily work in line with most amplifier/speaker combinations that’ll be used as sensible volumes in a home.
You’ll need:
A Bluetooth amplifier (to be sure the pins are the same use a SANWU 50W+50W TDA7492 CSR8635)An LP395Z transistor (a FET or any other transistor with built-in protection resistors will do)Two, 2x Relay boardsSome wireA board to mount everything on”

Link