IMPORTANT: This is not a comprehensive demo, and I will only leave it public until I have a chance to build a fully-functional version. It's purely to show the basic sounds of the design!
The Cardinal Tremolo is a vactrol implementation of the Harmonic Tremolo from Fender's 1960-1963 tremolo-equipped amps (the Super, Pro, Twin, Showman, and Concert models). A huge amount of credit for the basic design of this effect for stompboxes goes to RG Keen, who created a FET-based implementation. This vactrol-based implementation has some nice benefits, not least of which is that parts matching is not required, and it uses a far simpler chip-based LFO (or the TAPFLO chip). Additionally, the topology allows a simple switching mechanism to go between the harmonic tremolo and a "normal" tremolo.