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This article by John Simonton describes the assembly of the predecessor to the 2720R modular synthesizer offered as a kit package or individual modules through PAiA catalogs in the 1970s and 1980s. The 2720R had an actual AGO style keyboard and updated electronics (2720-8 sample/hold and voltage divider boards) and with options for a 2720-9 glide retro-fit board/control. This DIY magazine artilce project included modules and circuit-board-kits for the following items:

2720-1 VCA
2720-2 VCO
2720-3B Bandpass VCF
2720-3L Lowpass VCF
2720-4 Envelope (Function) Generator
2720-5 Control Oscillator (LFO)/Noise Source
2720-6 controller Vinyl Strip
2720-6 controller cv Sample/Hold
2720-7 Power Supply