3340 VCO

Voltage Controlled Oscillator
The base of any synthesizer, the Oscillator.

CEM3340,  used in many a classic 80s synth, can easily be tuned to 1 volt per octave making it really easy to integrate into a modern synth design or modular design.

Taken from the data sheet of the CEM3340.

Output Waveforms

A few things to note about the CEM3340 or the clone AS3340 are the voltage outputs.
The saw wave is 2/3 of the supply, Triangle is 1/3 and the square is 1.5V below the supply.

On a 15 volt supply, which I recommend, the voltages will be:

Saw: 10v
Triangle: 5v
Square: 13.5v

The square is easy to bring into line with a 10 volt zener diode.
The triangle can be amplified with an op amp or a a smaller summing resistor on the input to a VCA or filter, or op amp mixer.

Voltage Controlled Oscillator video:

Power Supply

The chip is quite flexable, apart from the waveform output voltages, to run on a range of supplies. I recommend a stable +15 and -5 volt supply, this way we can eliminate the extra resistor for the internal zener.
The internal zener not operating will reduce heat slightly inside the chip which could improve tuning stability.

A good well smoothed supply is needed, .1uF bypass caps close to the chip on each supply. If the oscillator doesn’t seem stable, put a bigger cap on the supply and it will get better.

Sync Inputs

If not required, ground  via the .1uF capacitor shown in the diagram.

There are a few ways to sync these chips, if you look at the datasheet it’s all documented. The method I use is the very last page, figure 5 conventional hard sync which resets the triangle core. You can’t use the triangle output of the synced oscillator, only the master.