Hardware Analogs with Sine waves? – Hardware (Instruments and Effects) Forum

It’s because most analogue oscillators use charging/discharging capacitors to create a triangle or saw “core”. This mechanism is easy to hard-sync by shorting to ground, and saw/tri/square/pulse waveforms are derived fairly easily. (PWM is achieved by changing the reference voltage of a comparator on a saw wave.)

Deriving a sine wave from saw/tri is more difficult; it requires a carefully designed and calibrated waveshaper and still the result will be approximate with some harmonic content.

It is possible to get very pure sine waves from a self-oscillating VCF, but this would be an independent “core” – quite difficult to extract saw/tri waves from, and not very responsive to sync.