Dual OTA VCO

Two VCOs on a triangle core design built round operational transconductance amplifiers (OTAs), from a building workshop. They range from about 19 Hz to 9.5 kHz, are quite simple with reasonably low drift, and can be tuned to 1V/oct, though not rock steady: a trade-off between component quality and design complexity against drift and accuracy. Each outputs triangle, square and pulse waves, its pulse width set by a knob or a CV; both have CV inputs for pitch, with coarse and fine knobs, and one has a soft sync input, the other an FM input. Try all kinds of CVs and audio-rate signals in them.

Key features

• Each VCO: cv and pwm in, tri, sqr and pulse out; sync on the left one, fm on the right one
• fine, coarse and pulse width knobs for each
• 14 HP; Nonlinearcircuits publishes no current draw, depth or assembled price (it sells the DIY PCB and panel), and ModularGrid lists none