Dual passive ring modulator
Two ring mods in a 4HP module. Classic transformer-and-diode design, using MIL-spec miniature audio transformers and 1N695 germanium diodes. Powered by the input signals, no separate power connection; in synth electronics this is called a "passive" module for that reason, despite the presence of active components.
Module is available as a DIY project only.
No info about availability.