The RK3 is the latest version of our classic R-53 and TM-1 devices.
We've boiled the circuit down to its bare minimum size and form factor: one tube (a 14BL11 "Compactron" originally used in TV sets) in the 4x4 RS* format.
It's very difficult to explain the RK3 in terms of "conventional" solid state electronic music equipment. It uses the tube in a way never seen before -- until Metasonix came along. Waveshaping is provided by our special vacuum-tube "pulser" circuit that spits irregular pulses onto the input waveform. The pulses synchronize erratically with the input pitch (if a waveform with sharp transitions is used). Interaction and a strange sort of "resonance" occurs with the input pitch. The effect is very roughly similar to a (very weird) PLL sound effect. Combined with true vacuum-tube circuit distortion and primitive ring modulation, this can provide a vast range of complex, aggressive distortion effects, utterly unique in the world. It will take you years to fully exploit the RK3's range of effects.
A basic ring-modulation function is also available in the unit--applying a carrier pitch from an external oscillator to the screen grid of the pentode, this allows making inharmonic sum-and-difference pitch sound effects, with a unique vacuum tube pentode sound. The carrier input can also be fed with control voltages.
RK6 resonant lowpass filter
The RK6 is a TOTALLY UNIQUE product, one that never existed before. It is a Sallen-Key two-pole lowpass filter with a feedback loop, to allow it to resonate. There are no integrated circuits or transistors in the signal path. It is a PURE TUBE design, the sort of design that might have been invented in the 1950s if anyone had dared to create a tunable lowpass filter for musical uses before the 1960s. It even uses a coupling transformer to provide the proper phase of feedback signal --- purely a “classic good old days” approach, and one rarely seen in the 21st century. It is the most primitive general-purpose lowpass filter the world has ever seen and probably ever will see. No, it does not simulate any other product and it does not sound like anything else.
Two “vactrol” optocouplers tune the filter, and another coupler allows CV control of the filter’s resonance. The RK6 may be used as a conventional lowpass filter or as a lowpass gate, as adjusting the TUNING control and CV input can almost completely cut off the signal.