HIFI Amplifier Switch
2 Amplifier 1 Speakerset, the Wife issue...
It is a HIFI DIY switch that automatically switches between the 2 Amplifiers, depending what is running!
Im using it to select between a Yamaha AX and a Marantz AVR, just to watch TV the Marantz is more than enough.
But when Music is on, it needs the OMPHHH from the Yamaha :D
Problem is that this would require to switch out cables all the time, or always switching on manualy the Yamaha.
There comes the "Wife Acceptance Switch" into play! If the Yamaha is Off, Speakers go to the Marantz, and vise versa.
Also there is a safety that whenthe Marantz is already power on and the Yamaha gets turned on, it does not switch! SWEET!
The Yamaha has some switched plugs in the back, there goes a small 12V power supply for the circuit.
The Marantz has a 12V remote output, that is used for the safety feature.
But what Relays? They should under no circumstances have a impact on the sound. So the same type of Relay is used as in the Yamaha Amplifier Output stage. They are capable to run something around 2kW, that is more than enough for my system.
So first a Logic Table is made to see whats needed:
That is a Inhibition Gate (AND with input negotiation), so lets build it with Transistors, fully Analog, no µC with baad noisy oscillators here, this is HIFI:
The 12V Supply is in the remote ports from the Yamaha Amplifier
Next is the Layout, the Audio path is kept as short as possible, and nothing is there what oscilates, pure analog.
I made the board myself using the toner transfer method, then foam etching it, solder layer on it, drill it, another toner transfer step for the labeling:
here are the Gerber Files and the PDF so you can make it: