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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 an 8hp module.

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.



Audio demos made by Josh Humphrey of Big City Music, using Analogue Systems rs95 and Plan B Model 15 VCOs:

Demo 1Demo 2Demo 3Demo 4Demo 5

Power requirement: +12v dc, 400 mA and -12v, 10 mA. As with all our modules, it draws about 2.5 times the operating current during “cold” power-up, and you must insure your power supply can handle the inrush current. See our support section for more information and power supply suggestions.

The Metasonix RK-series of vacuum-tube modules is intended for use in any “Eurorack” standard modular synthesizer system. All RK-series modules are 8hp (40.7mm) wide and fit in any Doepfer(tm), Analogue Systems(tm), Monorocket ™, or other compatible cabinet. They are powered entirely from the cabinet’s internal +-12v dc power supplies, using Doepfer compatible 16-pin power connectors. Their circuits protrude behind the panel less than 31mm (1.2 inch). All vacuum tubes in our products are NOS (new old stock) types from classic American and European manufacturers that are run very conservatively for long life, and are readily available from distributors. The 14BL11 tube in the RK3 protrudes from the panel for visibility and cooling, less than 38mm (1.5 inches), and will fit inside a Doepfer A-100 suitcase cabinet lid or into a Doepfer mini case, or under a Monorocket case lid. All audio inputs and outputs and CV inputs are 100% compatible with other synthesizer modules. Plate voltage is provided by a tiny switching supply producing clean 48v regulated at low current, which is very safe and will not injure the user. Potentiometers are top-quality Alpha RK12L types, and 3.5mm phone jacks are special Kobiconn vertical-mount types, much better quality than the cheap ones usually seen in Euro modules. Each RK-module is fully protected against reverse supply voltage, overvoltage, undervoltage, or incorrect hookup to external equipment. So stop worrying!  As with all our products, the RK series is totally handcrafted in Northern California, USA.