Yamaha CS-15: Duophonic improv w/ Korg SQ-1 - 2 separate voices in one monosynth

video upload by DreamsOfWires

"A simple melodic experiment with the two-voice architecture of the vintage Yamaha CS-15 from 1979. This synth has two separate pairs of control inputs to address two VCO's, filters and ADSR envelopes, each with a VCA. Voltage control uses the less popular Hz/Volts system, also employed by early Korgs such as the MS-20, which is why the SQ-10 sequencer supports it (since the MS-20 Mini re-issue also adopted it).
The range of reachable notes is limited using this sequencer, at least in the lower range, but I was surprised how well it worked, immediately after hooking up the CV A and CV B outputs to the CS-15's VCO 1 & 2 inputs, followed by the GATE A & B outs to the EG 1 & 2 ins. In the next CS-15 video I'll experiment with using the two-voice function in a slightly different way, with another popular sequencer. After that I'll probably focus on using it entirely as a monosynth with some sound examples.
The CS-15 is an odd synth - being able to divide it up into two (albeit very simple) monosynths is very unusual. In fact, I titled the video 'duophonic', which is debatable: The Arp Odyssey is famous for having a duo function, where the pitch of the two oscillators can be divided by the keyboard, but still sharing the same filter, envelope and VCA, and as such not creating two entirely separate voices. The CS-15 is more polyphonic in potential, and so a controller capable of polyphonic voice allocation could use it as a two-voice polyphonic synth. Not especially useful given the single oscillator per voice, but neat nevertheless.
What is most strange is that there is only one shared audio output, meaning that the two voices can't be processed individually. Stranger still is that the larger CS-30/CS-30L has individual outputs for both voices, but does not have separate control inputs for them! It's almost like the design blueprints for both synths somehow got mixed up in the factory.
However, with 2 fully-featured multi-mode filters (low pass/band pass/high pass), two full ADSR envelopes, which can be assigned to any combination of both filters and both VCAs, individual LFO level to pitch and PWM on both oscillators, white noise or external audio input, with Glide AND pitch bend... this really was a highly flexible/capable, well-designed, and well-constructed synth for the time. Important to note though, is that the filters will not self oscillate at high resonance levels, a bit like the early Oberheim SEM etc. The filter mode switches on mine are a little temperamental, probably a sign of age/need of servicing, but otherwise it's built like a tank.

I make videos to promote myself as a musician, and sell music on Bandcammp, which earns a few pennies to help fund what I do. My music can be found here: https://tomorrowthecure.bandcamp.com"