6581 Audio output - libsidplayfp/SID_schematics GitHub Wiki
The volume stage opAmp drives the gate of a big NFET which works as a buffer (In the 6581, resistors of higher resistance always are a NFET with the gate tied to +12V). That buffer is sending a current from +12V into the Audio Output pin, which means there always need to be a pull_down resistor to GND outside the SID at that pin.
