With vintage amplifiers, you have limited input switching capabilities. And they are all manual.
This projects aims to solve this problem.


I have an old kenwood KA-4002 (http://www.hifivintage.eu/product.php?id_product=476) which I love.


So, my solution to this problem, automatic audio input switcher.
Basically, the system will detect which audio input has a signal, and switch to it using a solid state MUX.

The project is in early state. Prototype circuit works on a breadbord. First test PCB done and sent to the factory.


Operations:
Stereo input is muxed using 10k resistors and AC coupled into an amplifier. (100x)
Then, the signal is compared to a reference voltage using a comparator which charges a CAP.
A MCU will then poll the output of the comparator and trigger the MUX (ADG409) to switch on the output.


The source code is available on github (kicad): https://github.com/zehome/autoaudioswitcher

BSD Licenced.