CEM3340 VCO

CEM3340 based VCO PCB

Features:

• Sine, Triangle, Sawtooth, and variable Pulse waves simultaneously available.
• All waveforms +/- 5vpp.
• Three 1 volt/octave inputs, linear FM, sync (choose hard or soft), and PWM modulation inputs.
• Onboard voltage regulators and reference voltage generators for stable tuning.
• Input voltage can be either +/- 12 volts DC, or +/- 15 volts DC.
• Designed to either plug into a separate carrier pcb with pots and jacks, or mount to a bracket and wire by hand.

A note about the pulse waveform:

This design does not use the built in CEM3340 pulse generator. Instead, an typical opamp circuit is used for the Pulse wave output. This is to avoid the influence of PWM on the frequency of the oscillator, which has been reported to be a problem, especially with the AS3340 versions of the chip. The built in pulse generator is disabled by tying the output to ground through a resistor, and hardwiring a negative voltage into pin 5 which permanently sets the pulse width to zero percent.

Status of the project:

Informal evaluation:

I've built three of these, and they work well and are fairly easy to build. The dual NPN in the sine shaper is a little small, but after doing a few of them I can solder them reliably without any grief.

Calibration is pretty straightforward and they tune up nicely and don't drift badly with changes in temperature. I have not done any rigorous testing, just by-ear, but I'm pretty picky about out of tune VCOs and these seem good to me so far.

Overall quite happy with this VCO.