Eurorack DIY 001 – AS3340 VCO
Introduction
A Voltage Controlled Oscillator (VCO) is one of the core components of a modular synthesizer. It can generate a waveform whose frequency can be controlled by an input voltage. The input voltage is usually normalized so that one Volt corresponds to one octave in pitch.
The AS3340 chip is a reissue of the legendary Curtis CEM3340 VCO IC, which was used in many of the synths of the 70s and 80s. It is a monolithic IC which just needs a few passives, and therefore perfect for my entry into the DIY modular synth world.
Features
- Four waveforms: rectangle, sawtooth, triangle, sine
- Pulse width control for rectangle
- Hard and soft sync inputs
- 1v/Oct and linear FM inputs
- Buffered outputs
Schematic
R9 controls the smoothness of the sine wave output, which is created from the triangle wave created by the AS3340.
R10 and R11 are used for tuning the oscillator.
References
[1] https://www.alfarzpp.lv/eng/sc/AS3340.pdf
[2] https://electricdruid.net/cem3340-vco-voltage-controlled-oscillator-designs/