Doepfer A-110-1 VCO

The Doepfer A-110-1 VCO is a voltage-controlled oscillator. This VCO's frequency range is about eight octaves (15 Hz - 8 kHz). It can produce four waveforms simultaneously: square, sawtooth, triangle, and sine wave. The frequency or pitch of the VCO is determined by the position of the octave (Range) switch and tuning (Tune) knob, and by the voltage present at the CV inputs. Frequency modulation (FM) of the VCO is therefore a possibility. Footage (the octave of the fundamental) is set by the Range control in five steps, and Fine tuning controlled by the Tune knob by about ±1 one semitone (can be modified for a wider range).

You can control the pulse width of the square wave either by hand, or by voltage control - Pulse Width Modulation or PWM.

The core of the A-110 is a sawtooth oscillator (in contrast to the A-111-1, which is based on a triangle oscillator). The other waveforms are derived from the sawtooth by internal waveform converters. As the sawtooth reset (i.e. the back-to-zero slope) is not infinite fast but takes a little bit of time the derived waveforms triangle and sine are not perfect! At the top of the waveform they have a small glitch or notch that is caused by the sawtooth reset and cannot be eliminated by the waveform converters. The sine is derived from the triangle by a simple diode-based converter and the sine shape is not perfect (only a rounded triangle).