TONESTAR 2600 is an ARP® 2600-inspired synth voice 31 years in the shaping, pre-patched like Pearlman's prodigy, and fully modular, allowing for highpass/bandpass/notch filter tones, and bristling X-mod effects. Connect CV / gate and twist 'n' switch, or pull its tones and voltages apart one 3.5mm cord at a time. 26 knobs, 7 switches, and 21 jacks make for complex and satisfying signal flow, colour and collisions. If it gets reedy, route the triangle wave 'round the VCF, and keep it boomin'.
Caswell Knowledge (circuit designer): "The VCO is the same affair as the Oscillation, the Boomstar, and the Omega. It's kind of a combination of Arp®, Oberheim® and Moog® circuits (sort of a greatest hits), time-tested, very stable—very good tracking over a very large range; certain parts have to be hand selected to achieve that level of exacting performance."
Envelope FYI: The Tonestar Sustain control replicates the behaviour of the 2600 and Odyssey: after the initial Decay, it continues to move (sink) very slowly, adding a little extra texture to the sound. It's technically a flaw, but after digging out my Odyssey, it is for sure a desirable "quirk", and the perfect companion to the 4072 filter.
Another bit of fun: The LFO is voltage controlled, so you can envelope, LFO, or otherwise modulate both the rate and the depth; the ADSR amount is also voltage controlled, so it can be manipulated by MIDI dynamics, MIDI volume, an LFO, etc. Greg [St. Regis] has decreed that anything must be patchable to anything, so some technically wrong patching (for example, pulse wave out to ADSR out) may often produce unexpectedly interesting, x-mod/notch filtering—quite pleasing effects
The Tonestar was Greg's concept, but as I understood it, the goal was a single oscillator, 2600 VCF, pre-patched and yet fully modular classic synth voice, at a specific size, wielding every trick we could cram in. Main use would be as a go-to bass line/lead tool, or a premium quality, entry-level, complete synth module, for root-to-leaf sound design, and multiform analog exploration/expression."