The Metasonix R51 Eurorack VCA/Distortion Synth Module

The Metasonix R51 VCA/Distortion Synth Module is a unique voltage-controlled VCA for Eurorack modular synthesizers.


The r-51 is unique and never before available in any form. It uses two remote-cutoff pentodes, type 26a6. two cv inputs are available for controlling circuit distortion from less than 2% up to more than 40% (varies with individual tubes). two cv inputs also allow use of the r-51 as a conventional synthesizer vca, with gain variable from less than -75db to +5db (typical).

Both distortion and vca features can be used simultaneously. This allows true vacuum-tube asymmetrical soft clipping to be applied to any waveform. with suitable cv processing, the r-51 can be configured as a true “variable mu” limiter or expander.

If you’ve had a chance to use the Metasonix R51, leave a comment!


Power requirement: +-12v dc, 150 ma.

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. 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 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 or into a doepfer mini case.

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 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,.

Each r-module is fully protected against reverse supply voltage, overvoltage, undervoltage, or incorrect hookup to external equipment. The r series is handcrafted in Northern California, USA.

Audio demos are available at Analogue Haven

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