Blast from the past: esoteric question about original uMod

Greetings, folks. I hope I’m not broaching a topic that’s too dusty for consideration. I have both an original uMod and a uMod II in my rack; I regularly use the former for audio/ringmod duies, and the latter for CV munging and logic. I really like that the original uMod has separate AC an DC inputs which can be used simultaneously. I especially love to create drones by ring-modding two audio sources and then modulating one or both of the DC inputs.

My question: when both AC inputs are in use, how do the voltages coming into either of the DC inputs affect the output? My first guess was that the DC voltages were offsetting the respective AC input, but I tried a manual comparison by offsetting the incoming AC voltages in the same way with a mixer, and they sounded nothing alike. (I looked for a uMod manual, even with, but couldn’t find anything.)

This isn’t a critical question, obviously, but I’m curious and interested in learning how this old warhorse it works. Thanks.