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"Yamaha's SK-series are combo-keyboards with synthesizer, organ, brass and string sections. The SK-10 was the first of the SK-series, released in 1979 - the SK-20, 30 and 50D followed in 1980, and the SK-15 in 1981, possibly as a replacement for the SK-10. The SK-10 is the only one in the series that does not incorporate a synth section, but has organ, brass and string sections that can all be played together for more interesting combinations. Very sturdy casing, 4-octave and fully polyphonic the features also include a leslie simulator, vibrato, attack and sustain rocker switches, a slider for 'brilliance' and a one-octave transpose switch. Not exactly feature-laden, but a lovely string synth sound. Interestingly, they are often referred to as 'analog', but in fact do have a digital section. Its organ has one of the early implementations of Yamaha's FM technology in a very limited form, concurrent with the GS-1/2 development platforms which eventually led to the DX series.