The RK2 XS-VCA is the ultimate vacuum-tube VCA. It isn't merely a tube VCA, in fact. It's also-
* a TUBE preamp with gain of approximately 30 dB
* an inverting/non-inverting amplifier for stereo and signal-canceling effects
* and/or an extreme distortion effect.
It can be set to simply be a plain vanilla VCA, with moderate tube distortion. Overdrive it for beautiful slow-onset clipping distortion. Or turn up the FEEDBACK control and beware.
What does it sound like? Imagine a slightly tubby tube amplifier, suddenly turning into a screaming chainsaw. And flying around the room to break your sappy bleeps and bloops. A bulldozer on fire crushing your nads. Strange tentacles of doom rise up from the bottom of the ocean and slap your mother's asscrack.
Or you can have anything in between. All voltage controllable with one CV input.
Trigger and CV inputs have 100k ohm impedance. The maximum audio output is "hot" (up to +10 dBu) and able to drive a 600-ohm load. The CV input may be anywhere in the -10v to +10v range – the effective range is -2v to +10v.
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 4U Buchla 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.
RK4 Filter / VCO
The RK4 is the minimized version of our R-54 Supermodule,
It uses a triode-pentode in a unique Wien-bridge circuit, to provide clean sine-wave oscillation. Using a Vactrol, the pitch of the RK4 is sweepable from less than 20 Hz to more than 2 kHz, continuously, via front-panel control or a CV input. By adjusting the waveshape/resonance control, the sinewave signal produced by the RK4 can be trimmed to less than 10% THD (depending on operating pitch)---with NONE of the problems inherent in solid-state oscillators and sine waveshapers. Because the Wien bridge contains no piecewise sine shaper or amplitude-control circuit or component. The tube itself performs that job. So the distortion products are entirely low-order, unlike the "sine waves" that solid-state VCOs or samplers produce.
Turn up the RESONANCE, and the oscillator output gives a unique soft-clipped square-wave sound. The simplicity of the RK4 will fool you--its behavior is odd and radical, and years will be required to fully explore all of its quirks.
Now for the special trick. Plug an audio signal into the audio input. Instantly, the RK4 transforms from a VCO into a bandpass resonant voltage-controlled filter, with the same range as in VCO operation -- 20 Hz to >2 kHz. Its behavior and sound are unique. Again, you will be kept busy for years exploring all of its strangeness.