Moog CP-251 Control Processor
Four CV inputs, a lag processor, an LFO, sample-and-hold, and a noise generator in a box that turns a pile of Moogerfoogers into something resembling a modular system.
Overview
The CP-251 is the least glamorous box in the Moogerfooger line and probably the most useful. It makes no sound of its own. It supplies the control-voltage plumbing that the stompboxes assume you already have - mixing, splitting, attenuating, lagging, randomizing, and oscillating signals that tell other voltage-controlled gear what to do. Big Briar sold it for $299 when it first appeared.
The front panel is where the action is, and that's deliberate. The other Moogerfoogers put their jacks around the back, facing away from the player, which is a real annoyance when you're patching on a tabletop. The CP-251 keeps its jacks on the lower front panel, close to the knobs, so you can reach them while you're twiddling. It's a 4U-width unit and can be rack mounted when you want it out of the way.
The mixer section takes four CV inputs at once. Two of those inputs deliver +5V to the ring for expression pedals. The other two supply -5V to the tip for general CV duties. There are two input attenuators, a master gain, and an offset-level knob. The mixer puts out both a normal and an inverted signal, and the second output is 180 degrees out of phase with the first. That inverted output comes in handy when you need to drive two destinations in opposition.
Four multiple jacks let a single control source fan out to three destinations. A pair of attenuators, each with its own input and output, let you trim a CV's amplitude with a knob instead of a menu. The lag processor gives independent rise and fall control, variable from 1V/second up to 1V/ms. That's slow enough to smear a stepped sequence into a glide and fast enough to be nearly transparent. The voltage-controlled LFO puts out triangle on one jack and square on another, with a range of 0.2 to 50 Hz, sweepable from the Rate knob or an expression pedal plugged into the pedal input. A white-noise generator serves as either an audio source or a randomized control signal. The sample-and-hold has two outputs. Out 1 produces stepped random voltages that change at the LFO rate when nothing external is patched in, and out 2 is a smoothed version of the same for gentler, continuously varying modulation. There's a trigger input as well.
The CP-251 is virtually a must-have for anyone integrating several analog synths or other CV-controlled devices. Sound On Sound UK (2003, p.33) noted that Moog's innovative spirit remained undiminished more than 30 years after he created his first portable synthesizer. The reviewer's verdict was that it brilliantly borrows from the modular analog synthesis tradition and provides enormous flexibility in reshaping modulation. The same review suggested a practical test - patch it into a signal processor or two, plug in a guitar, and see what happens.
Two things are worth flagging for anyone shopping today. First, the CP-251 has no oscillator of its own. In a Moogerfooger-based pseudo-modular, tone sources come from elsewhere in the line - the LFO and carrier oscillator of the MF-102 Ring Modulator, the LFO of the MF-103 Phaser, the resonant filter of the MF-101 - with the CP-251 contributing its own LFO and noise. Second, the price drifted. The unit launched at $299. Both figures show up in print, so treat the earlier number as the original street price and the later one as the going rate in the years that followed.
The CP-251 does not store anything. It is all analog, and every setting is a physical knob or a patch cable. For studio work that's fine, since you patch a modulation chain once and it stays patched. For live use it suits players who build a fixed rig and leave it alone. The classic use is the sample-and-hold patched with white noise into a filter cutoff or pitch input. The smoothed second output turns the same random source into a slow, wandering drift rather than a staircase.
Collectors tend to file the CP-251 under "utility" rather than "instrument," which keeps prices saner than the more famous Moogerfoogers. It's also the piece most likely to be sold off separately when someone breaks up a Moogerfooger collection, so examples turn up with some regularity. Buyers should confirm the unit is complete and that the pedal-input jacks behave. Expression-pedal wiring is the most common thing to go wrong on any CV pedal input, and the CP-251 has two of them. Beyond that, there's little to fail: no displays, no memory, no firmware.
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