A remake of the Phoenix Microtechnologies AP420 with mono input and TRS microphone jack.
The schematic is per the PDF manual in the respository from the Phoenix Microtechnologies AP420. I added a second RCA jack so you can hook up stereo sound and it will be combined to a mono input. There's also an updated microphone jack that supports TRS 3.5mm and goes to a mono input. The selector switch on the board allows you to select between the RCA input and the microphone input. VR1 is a gain control knob for adjusting the strength of the audio signal.
The AP420 manual also goes into some detail in the notes section for performing component changes to allow for different audio sample rates at the expense of audio quality.
This device hooks up to the parallel port of of an Amiga 500, 600, 1000 (with adapter), 1200, 2000, 3000, and 4000. It does not require any external power.
Not built and tested yet. Feel free to evaluate the circuit and provide any feedback.