Next up is the audio amplifier, speaker, potentiometer and the headphone jack

The amplifier has to be modified a little bit in order for it to shut down when headphones are plugged in.

For that, pin 12 needs to be desoldered from the board, and a wire soldered to it. It is the shutdown pin. We need to solder on a 10K or 20K pullup resistor to it and VCC, or the amp will stay off all the time:

Then the potentiometer is wired to the pi, the amp and the headphone jack:

And then I wired the speaker to the amp and glued everything in place: