Analog VCOs use either a sawtooth core or a triangle core, each producing different waveform strengths and weaknesses

Analog VCO oscillator circuits are built around one of two primary core topologies. The sawtooth core starts at a high voltage, falls linearly to a low voltage, and resets instantaneously. Its strength is producing a clean sawtooth wave and square wave, and a good ‘hard sync’ sound; it is harder to derive a clean triangle or sine from it. The triangle core rises and falls at equal rates, turning around at each extreme without resetting. It produces a cleaner triangle and sine wave but may yield a less perfect sawtooth. The choice of core shapes the set of waveforms a VCO can derive cleanly and its sonic character — a pure engineering decision with audible consequences.

Examples

AJH Mini Mod: triangle core recreation of the Minimoog oscillator — strong sine/triangle. Doepfer A-110-6: triangle core yielding the trapezoid waveform. Sawtooth-core VCOs: easier to sync, strong saw and square, sine needs shaping.

Assessment

Describe in three sentences what happens electrically in a sawtooth core VCO and why it is easier to produce a square wave than a sine wave from it. Then explain why a triangle core makes reversal/flip sync easier.