A monophonic analog synth produced by Crumar in 1982. The Spirit is noted for its extensive modulation options, and for the fact that Crumar employed several ex-Moog Music employees, including Bob Moog himself, to do the design work.
The basic synth architecture contains two voltage controlled oscillators, two voltage controlled filters, two voltage controlled amplifiers, two ADSR envelope generators, and two low frequency oscillators. The VCOs are referred to as A and B; the B oscillator can be offset from the A oscillator by an interval or by one or more octaves, and it can also be synced to the A oscillator. Usefully for the purpose of obtaining unusual tones when using oscillator sync, the B oscillator can be uncoupled from the keyboard control voltage and tuned to a fixed frequency (possibly modulated by one of the LFOs), a feature that is also useful when using the ring modulator.
The two oscillator outputs are routed down two separate signal paths. The first path routes the oscillators to a mixer (where they can be combined with an external input) and then to the pair of VCFs and a VCA. The two VCFs are referred to arbitrarily as the "upper" and "lower" filters. The upper filter is a low pass filter that can be set to a 2- or 4-pole response. The lower filter can be set to a bandpass or high pass response, or it can engage a distortion circuit. The cutoff frequency of the filters is swept by a dedicated envelope generator, although the lower filter can be uncoupled from the envelope.
The two LFOs are referred to as "Mod-X" and "Shaper-Y", with a number of routing options for each. Unusually, the Shaper-Y can also be used as an attack-decay envelope generator, and it is this that controls the VCA for the second audio signal path, referred to as the Shaper-Y path. The mixer for this path allows the A and B oscillators to be mixed with the ring modulator and a noise generator; it also contains a (non voltage controlled) low pass filter. The Shaper-Y LFO/EG can be gated or triggered in any of several modes, allowing for repeating envelopes that can operate independently of the keyboard gate. Unusually, there is a mod wheel for each LFO, and each one has a rotary switch for choosing where the modulation should be routed when the corresponding wheel is operated.
The extensive modulation options allow for more complex timbres than are usually possible with most performance synthesizers. A generous set of control voltage inputs and outputs on the rear panel allows for further interfacing with external equipment. The two audio paths are available as separate outputs, allowing for e.g., the two to be amplified separately, or one or both to be routed to other synths or external processing equipment.
Perhaps because the modulation operations baffled performers, the Spirit did not sell well at the time it was introduced. Perhaps less than 500 were made before Crumar dropped the model so it could devote resources to the development of the Bit One. But a number of collectors now view the Spirit as a hidden gem, with a sound quality as good as the popular 1970s monophonic synths. At one time they were available in the collector market at fairly low prices, but due to the low number made, the market has now dried up, and on the rare occasion when one comes up for sale, it sells at a price comparable to a Minimoog or Odyssey.