Dual Shape LM358 Oscillator

Here’s my take on the All About Circuits VCO that uses an LM358 OpAmp. Instead of having two independent outputs, I blend the triangle and square waves together. I also added a second CV input for pitch modulation.

I skipped the exponential converter section which would scale the output to the standard 1V/Oct. Instead, my version can be played in tune using the Hz/Volt standard. Luckily, my Beatstep Pro can be configured to provide such output through the included Arturia Software.

This uses only the GND and +12V rails of my power supply.


This circuit this is based on All About Circuits' DIY Synth Series.

Here’s my take:

Dual Shape Oscillator Schematics

My KiCAD files are on Github.


The output of my circuit can be a triangle wave, square wave, or a blend of the two. Level of each wave type is controlled by the Triangle and Square knobs.

Scope Output Triangle

The square wave output is a bit louder than the triangle. This could be addressed in future versions by adding either an attenuator at the square output or a boost to the triangle. But because this module has two independent controls for each output, it’s pretty easy to balance them out.

Scope Output Square

A sweet spot can be found by adjusting the levels of each waveform output.

Scope Output Blend

Let me know if you’ve built it! Tag me on IG @benjiaomodular.