R-54

Supermodule VCO/VCF

It uses a triode-pentode in a unique Wien bridge circuit, to provide clean sine-wave oscillation. Using a Vactrol, the pitch of the R54 is sweepable from less than 20 Hz to more than 5 kHz, continuously, via front-panel control or a CV input. By adjusting the waveshape/resonance control, the sinewave signal produced by the R-54 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 overdrive control, and the oscillator output clips the output amplifier pentode tube, for a uniquesoft-clipped square-wave sound. The simplicity of the R54 will fool you – its behavior is odd and radical, and it will take you months or years to fully explore all of its quirks.

Now for the special trick. Plug an audio signal into the audio input. Instantly, the R-54 transforms from a VCO into a bandpass resonant voltage-controlled filter, with the same range as in VCO operation – 20 Hz to 5 kHz. Its behavior and sound are unique. Again, you will be kept busy for years exploring all of its strangeness.

CV response: Hz/v. Use a suitable MIDI/CV interface, or use Metasonix R-60 interface to obtain perfect equal-tempered tuning every time.

Specification:-

• +/-12V Doepfer-style power connector
• alpha rk12l potentiometers
• kobiconn vertical-mount 3.5mm jacks
• tubes used: 19KG8, 6AK5
• Current Consumption: 250mA
• Panel size: 22HP