The Yamaha CS15 Analogue Synthesizer from 1979 - a forgotten beauty

Published on Feb 21, 2020 Alex Ball

"I've had a dozen requests to cover this synth and I said I'd do it if I was able to get hold of one and I'm glad to say that that happened.

The CS-15 is a two-oscillator analogue monosynth from 1979 that has an awful lot more to it than meets the eye. The signal and control routing is so much more flexible than many other comparable synths from this era that command legendary status and so I'm kind of baffled as to why the CS-15 doesn't seem to be held in the same high regard.

What's so good about it?

Two great sounding oscillators with triangle, sawtooth and pulse and a crazy wide range from clicks to stuff only dogs can hear.

The LFO runs up into the audio range and so the pulse width and oscillator frequency can be modulated at audio rate for cool cross mod and pulse-width distortion FX. This can be done discretely to either oscillator to taste.

The filters - There's two and they're multimode / state variable! Contouring can come from either of the two envelopes and can be positive or negative and you can do audio-rate modulation of the filter because of that LFO mentioned earlier.

The VCAs - There's two (notice a pattern here) and they can have their own envelope contouring and/or be modulated by the LFO (again right into the audio range).

Envelopes - There's (drum roll) two! They're super snappy or long and loose as there's a switch to extend the time period from x1 to x5. They can be triggered by an external signal as well as the keyboard.

Signal Routing - VCO 1, noise or an external signal can run through VCF 1. VCO 1 and VCO 2 can run through VCF 2.

Rear Control - CV and trigger? Yep, there's two of each. You can control the oscillators and envelopes discretely (I don't know of many comparable synths from this era that allow for that that aren't modular).

Anything else? Yes; portamento, glide (positive and negative and discrete for each oscillator), pitch bend and dual or signal filter control in the performance section.

So what's wrong with it?

LFO can't be retriggered with note on or clocked, there's no oscillator sync, the filters sound great but they're 2-pole and don't self-oscillate, there's no global LFO control in the performance section and despite being able to make two entirely different sounds at once, there's only a mono output.

But all in all, it's a very versatile and powerful synth considering its era and the prices have tended to remain less than even the Roland SH-101 which is far more limited. It's certainly much cheaper than an original Pro~One, MS-20 or Odyssey that are held in high regard (I have all of those and love them too btw).

Anyway, I hope this answers the question for those who asked it."