Here are some drony kind of sounds I recorded before selling my Yamaha CS-15 with the intention of showing some of the sounds the synth is capable of.
The CS-15 is a pretty flexible analog synthesizer, thanks to it having two of everything – except for the one LFO (which goes up to 1000 hz – fast!). The envelopes are fast and snappy, though not as powerful as the ones on the lesser model, the one-oscillator CS-10. But you can not demand much more from such a cheap and still well built synthesizer. Of course you are left wishing for some features – for example it is lacking in inter-oscillator modulation, no cross-mod, sync or the likes despite two oscillators.
The two state-variable filters (LPF, BPF, HPF) are not exactly “creamy” and pleasant in ways like the moog filter or the Roland SH-series – but they are very competent and useful when it comes to soundsculpting. They have a distinct character, and are not really bland sounding. Highly resonant sounds are not one of it’s strong points, but it does well across board otherwise.
Modifications can remedy some issues, for example enabling the option of routing the filter both in parallell and serial. Both filters in bandpass mode, serially connected, with separate CV-sources controlling the cutoff makes for some very nice sounding vowel type sounds.