The top-of-the-line model of a series of Analog synthesizers manufactured by Yamaha in the late 1970s and early '80s. The CS80 was known in its day as a somewhat quirky synth that was much loved by certain performers, and rather disliked by others. It is an 8-voice polyphonic synth that offers two layers per voice, with each layer settable to a patch independently of the other. It has independent controls for every voice parameter.
The basic architecture is that of a conventional VCO-VCF-VCA string per layer. However, the VCF actually consists of two filters, one low pass and one high pass. These could be coupled to form a bandpass filter, but each half could be set to track the keyboard at different rates, so that the passband varied across the keyboard span. The filters excelled at creating brass sounds; the CS80 and other models of the CS line were heavily used for this in the day. They could also, with the variable passband, create sounds that were delicate and chime-like in the upper registers, and simultaneously big and meaty in the bass. The synth also contained several built-in effects, some of which were borrowed from Yamaha's line of electric organs.
The CS80 was known for its performance features. The keyboard mechanism included polyphonic aftertouch, one of the first commercial synth designs to do so. A ribbon controller could be set to effect pitch or the filter, and it had an unusual feature: wherever it was touched first became the "zero point", and it would operate up and down from there until released. Then, the next touch became the zero point, and so on. (The CS80 had no conventional pitch wheel). A set of controls to the left of the keyboard allowed various effects to be switched in and out quickly. Two rows of buttons allowed for patch selection for each of the two layers; there were 10 presets and two programmable memories per layer, plus a "manual" button that transferred control to the panel controls. The patch memory was a crude hack; under a door at the upper left were four sets of micro versions of the panel controls which set the parameters for these, two for each programmable patch (one per layer). The preset memories could be altered with a soldering iron; their parameter values were determined by sets of resistors on a circuit board inside the synth. The panel controls themselves were of a peculiar design; they looked like sliders, but they were actually levers connected to the rim of a thumbwheel-like mechanism, which meant that they moved up and down in arcs rather than straight lines. Each slider was color coded to indicate its general function.
The CS80 was notorious for its weight (220 lbs. / 100 kg!), unreliability, and refusal to stay in tune. Also, there were no external CV/Gate jacks, and Yamaha never offered a MIDI retrofit, so there was no practical way to couple it to another synth. (Kenton has since offered a MIDI retrofit which allows the CS80 to be receive but not transmit MIDI messages.) Nonetheless, the CS80 is one of the most highly sought-after synths by collectors today.