The Model 15 was the smallest of the Moog modular synths, originally intended for schools and music colleges to demonstrate the basics of analogue synthesis and voltage control. (The largest being the Moog 35 modular, as used by Keith Emerson among others). With modular synths, the instrument consists of discrete modules – oscillators, filters, amplifiers etc – which the user patches together using cables. However, the set of modules that you got was decided by the manufacturer, unlike today’s Eurorack where users buy individual modules and slot them in as they wish. There are now several companies making ‘clones’ of the original Moog modules using modern components, which makes them a bit more affordable. Vyv uses a Model 15 clone by Club of the Knobs, with a couple of non-standard modules, namely an extra VCF (filter) and an extra VCO (oscillator) in place of the standard Moog static filter bank which would normally sit top left of the cabinet.