Hackaday Behind The Pin: How The Raspberry Pi Gets Its Audio Hackaday All the main Raspberry Pi board releases since 2012 with the exception of the Pi Zero series, have featured a 3.5mm jack carrying line-level audio. The circuits are readily accessible via the Raspberry Pi website, and are easy enough to understand …

The rest is here:
Behind The Pin: How The Raspberry Pi Gets Its Audio – Hackaday