CS-01
The CS-01 is a monophonic, single oscillator synthesizer with a 2 1/2 octave mini-sized keyboard, that can run on battery power or via a wall-wart AC/DC converter. It was obviously marketed to the young, first synth buyer, market. However, dispite it's mini-sized keys, it has been since adopted by many professionals for it's simple design, active sliders, and great sound. The one pictured above is grey with light grey lettering but they also came in red with grey lettering.
The voice architecture was quite simple. A single oscillator with a sub-oscillator, a VCF, an LFO. The oscillator has a slider for fine tune, and an other with four octave settings, with the fifth setting switching it to the noise source. Available waveforms are triangle, sawtooth, square, and narrow. There is also a pulse width modulation (PWM) waveform with a separate slider controlling the PWM speed. There is a slider for glissando (unfortunately, not portamento). The filter (12dB/octave) section has sliders for cutoff frequency, resonance, and EG (envelope generator) depth. There is a EG depth for the VCA. There is a switch for resonance (low and high only). The LFO can be switched to control the VCA or the VCO. There is a slider for LFO speed and the amount is controlled by the controller wheel. The envelope generator is a simple ADSR with sliders for each (attack, decay, sustain, release).
One of the best features was the breath controller input. The breath controller was Yamaha's foray into the "alternate controller" market, with the introduction of the BRC1. Few, if not any, manufacturers incorporated this usefull, if somewhat awkward and sometimes messy (spit) controller idea. However, if you are a brass or woodwind player who is used to control loudness and timbre by air pressure, the BRC1 is very natural. The mouthpiece is held in the mouth with your teeth as the performer blows air into it. The harder you blow, the more signal it sends. The breath control input has separate knobs for VCA and VCF (cutoff frequency) amount.
The CS-01 was sold as a part of Yamaha's Producer Series, including a headphone amp, stereo mixer, and headphones, so that it could be used in group practice. Needless to say the idea didn't catch on, at least outside of Japan, where rehersal space is somewhat limited. The CS-01 did come with a cool carrying case.
There was also a CS-01 II that was Black with green letters. In addition, Yamaha replace the filter with a better sounding 24dB/octave filter. They also replaced the resonance switch on the filter with a slider (good move).