Yamaha CS series
I’ve had several of the Yamaha CS-series synths: CS01, CS5, CS15 and CS40m. The first two are monophonic – just one note at a time. The 40m is properly duophonic – two notes simultaneously, each with full articulation. The 15 is a crossover, being monophonic from the keyboard, but as each oscillator has its own CV input jack round the rear panel, if you use an external CV source you can pitch each oscillator individually.
Below is a list of details, repairs, and modifications relating to the CS series that I will add to on an ad hoc basis.