In a series of videos, Marco Reps invites you to follow his Elektor Formant Modular Synthesizer Overhaul. His opening commitment says I'm gonna refurbish this old electronic music instrument in several episodes. Six have been published so far. While reconditioning, repairing, rebuilding and even redesigning, Marco recounts the resurrection of his almost 30 years old analog synthesizer.

These occasionally lengthy but invariably relaxing videos broach many different and sometimes surprising subjects, from Eagle CAD software, SPICE and other simulation software, to CNC based circuit board etching, not forgetting Ali Express and the use of mint flavor dental floss.

One of the most exciting installments looks at the 12 dB and 24 dB voltage controlled filter (VCF) modules and their theory of operation. Marco knows his stuff: ‘VCFs have almost no applications apart from music electronics, but the integrator amplifiers they're based on are highly interesting and useful’.
The following installment covers the trouble he had with the VCO modules.