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"This is an impossible module to find and it was just luck that I was able to get it so I’m selling it with great reluctance. It kicks ass. Blast and blast, it’s got power and intensity. Grab it before I change my mind.
It uses a triode-pentode in a unique Wien-bridge circuit, to provide clean sine-wave oscillation. Using a Vactrol, the pitch of the R-54 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 unique soft-clipped square-wave sound. The simplicity of the R-54 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.
And now, it's got two new tricks. A VCA CV input allows you to control the output level of the R-54 as well as the amount of clipping in the output tube. Plus, a HARSH switch introduces a feedback loop into the CV control. Turn up the output level and the R-54 does very strange things.
CV response: Hz/v. Use a suitable MIDI/CV interface, or use our R-60 interface to obtain perfect equal-tempered tuning every time. Maximum output signal, 12 v p-p. Power requirement: +-12v dc, approx 150 mA. (All specifications are approximate and may vary from sample to sample.) Tubes used: 19KG8, 6AK5.
WARNING THIS MODULE USES 400mA FOR START UP!"
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