Thyratron VCO

The R-55 is essentially one of the VCOs in our legendary S-1000 Wretch Machine, boiled down into a 22U Eurorack module. It produces the notorious “sharkfin” sawtooth waveform of thyratron VCOs, replete with the weird pitch variations and apparent “noisiness” of a thyratron oscillator. Our new for 2017 version has a premium engraved aluminum panel.

Turn up the overdrive control, and the oscillator output clips the output amplifier pentode tube, for a unique soft-clipped square-wave sound. The simplicity of the R-55 will fool you--its behavior is erratic and weird, it always sounds “broken”, and the waveform is “deviated” in every way. You don't even need to feed it Hz/v CV: just run a square-wave or pulse signal from a conventional VCO into a pitch CV input, and it will “force” the R-55 to track along with the other VCO.

CV response: Hz/v, giving about 1.5 octaves of usable range with a Kenton Pro-Solo MIDI/CV. Span and offset trimpots on front panel, adjustable to make the R-55 track roughly along with the Metasonix R-54 Supermodule, or with other Hz/v VCOs. Maximum pitch range, 60 Hz to more than 3 kHz (approximate), range with CV typ. 2.5 octaves maximum. Octave switch raises pitch range about 2 octaves. Input jacks: two CV for pitch, plus one that optionally controls the gain of the pentode clipping circuit, acting as a VCA. Maximum output signal, 20 v p-p.

Power requirement: +5v at 1.8 amps cold, 650 mA hot, plus +-12v dc, 50 mA.

Tubes used: 2D21/5727 thyratron, 6AK5 pentode.

(All specifications are approximate and may vary from sample to sample.)

WARNING: the R-55 draws a LOT of power from the +5v line when first powered up. Your cabinet MUST be able to produce 1.8 amps at +5v to warm up the tubes in the R-55. See our "Support" section for more information on power supplies, or use our RKP power system with the optional +5 supply. Doepfer and Kilpatrick +5v power adapters cannot supply this much current. In other cases, addition of a large +5v supply to your Euro cabinet may be required.

The Metasonix R-series of vacuum-tube modules is intended for use in any "Eurorack" standard modular synthesizer system. All R-series modules are 22HP (112mm) wide and fit in any Doepfer(tm), Analogue Systems(tm), or other compatible cabinet. The R-55 is powered entirely from the cabinet's internal +5v and +-12v dc power supplies, using Doepfer compatible 16-pin power connectors. Their circuits protrude behind the panel less than 25mm (1 inch). All vacuum tubes 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 tubes protrude from the panel for visibility and cooling, less than 38mm (1.5 inches), and should fit inside a Doepfer A-100 suitcase cabinet lid. All audio inputs and outputs and CV inputs/outputs are 100% compatible with other synthesizer modules. Plate voltage is provided by a tiny switching supply producing clean 95v 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 R-module is fully protected against reverse supply voltage, overvoltage, undervoltage, or incorrect hookup to external equipment. As with all our products, the R series is totally handcrafted in Northern California, USA.


  • 50 mA +12V
  • 50 mA -12V
  • 1800 mA 5V
  • 25 mm deep
  • Ø 4.67 (3 Votes) Average Rating

This Module is currently available.

$469 Price in € submitted Apr 15th 2017, 08:16 by severence | last Change Apr 20th 2017, 07:47 by severence

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