6581 Opamps - libsidplayfp/SID_schematics GitHub Wiki

The designers were not able to implement real OpAmps, so the amplifiers in the 6581 are self-centering inverters.

Each of the 6 amplifiers is built from 4 NMOS FETS, did draw white boxes around the FETs in this picture:

images/s6581_amp.png

Schematic of an amplifier:

images/6581_amp.png

Layout for all the amplifiers is pretty much the same, it's just mirrored sometimes to make better use of the space on the silicon.