Yamaha was very vague and secretive about their early FM instruments. In the GS manual there is only a single very brief mention of FM. The CP-25/35 has a mysterious YM722 Wave generator IC. Each of these IC's produces 8-voices. From what I've been able to determine from the service manual the CP-25 has two of these chips which allows a maximum of 16-voice polyphony and 8-voices when layered. The CP-35 has four YM722 chips and is always capable of 16-voices. Nowhere in the manual is there a description of how the Waves are generated. It is not likely Top-Octave-Division as each chip would generate 12 tones followed by Dividers and it would have full Polyphony. So it appears the 16 Tones are being assigned across the keyboard by a multiplexing system as found in Analog PolySynths and Yamaha's early FM instruments. The manual describes in some detail the Filters and Effects being comprised of discrete components which leads me to believe they were being tight-lipped about FM at the time. The CP-25/35 was introduced in 1981, the same year as the GS-1/2 FM keyboards. Yamaha had used a limited amount of simple FM technology for certain voicings in some of their organs and smaller keyboards before 1981. Judging by the sound of the CP-25/35 I would find it hard to believe it was generated by Analog Oscillators.
Last edited by V301H
on Thu May 15, 2014 2:50 am, edited 2 times in total.
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