Following the great guide of Dennis Bohn "Why not Wye
", I chose to integrate an easy summing circuit or actually two, one for each audio input.
A simple dip switch (ON-ON) for selecting the audio input for the amp. I added this to be able to connect other audio sources and to use the device as a 'normal' speaker, independent from the RasPi.
The selected amplifier was wired according to the datasheet. Basically it accepts input voltages from 5 to 12V DC and a mono input signal through an optional potentiometer for volume control. I connected a 8Ω broadband speaker, which sounds surprisingly good for only 10€.
I chose to integrate two separate power units to be able to independently turn off the amp/speaker while keeping the RasPi running. This is mainly due to the boot time of Raspbian of about 30-40 seconds. Because I had them laying around I used two plug-in adapters, one providing 5V DC (max. 2500mA) for the RasPi and the other providing 12V DC (max. 1500mA) for the whole audio setup.