A 4-voice semi-polyphonic analog string machine with a limited synthesizer section and a 49-note keyboard. Released in 1979.

The Delta is not a real polyphonic synth, with a system similar to the Mono/Poly: all voices sharing the same envelope. There is 1 VCO (with only the square waveform), 1 resonant VCF, 1 VCA with an ADSR envelope generator, plus a sine-only LFO. A noise generator is featured, as well as a joystick for modulation/pitch.

With its severely limited capabilities, the Delta isn't very useful as a synthesizer. It also uses Korg's non-standard Hz/voltage interface, so it isn't compatible with synths from other manufacturers without a third-party converter. Reportedly one can turn the Delta into something more interesting by tweaking the trimmer pots inside to make the VCO self-oscillate.

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