DIY VCO Eurorack module with saw, triangle, square, and sine output.

This is a minimal, hand soldered, sawtooth core VCO module I designed to be inexpensive, fully analog, and with a variety of outputs. To that end, the module features sawtooth, triangle, pwm, and sine outputs, with pwm, fm, and pitch inputs. It internally features temparature tolerant circuitry, as well as having coarse and fine tuning, as well as pitch scale.

DIY eurorack modules are not particularly uncommon, but they often come at the cost of features. A lot of the time such modules lack functionality common to other prebuilt designs, and I wanted to change this. This module has a full standard feature set, including proper PWM and sine outputs.

Also, a lot of eurorack modules are quite bland in terms of design, often lacking any personality and focusing purely on cramming as many knobs in as possible. Here I've taken time to add some (imo) nice art and some extra space on the module.

This should be pretty self explanatory:

• The pitch knob controls the pitch of the module. If using CV pitch, be sure to set this to the minimum.
• PWM input adjusts the width of the PWM output. The knob to the right of it controls the scale of the PWM CV.
• FM input modulates the frequency by the CV input. The knob controls the FM scale.
• Outputs are along the bottom! Sawtooth, Triangle, PWM, and Sine, in that order..

Hopefully, once you've received your pcb and soldered it up, it should look something like this:

Before you properly use it, you'll likely want to tune it. This can be done by following these instructions::

1. Turn the pitch knob on the front of the board to the minimum.
2. Adjust the coarse trimpot on the back until the output is roughly A0 (~27.5Hz)
3. Adjust the fine trimpot to accurately tune the output.
4. Send 5V into the 1V/OCT input on the front of the board.
5. Adjust the scale trimpot until your output is roughly A4 (~440Hz)
6. Repeat steps 2-5 several times until tuning is accurate at both A0 and A4.

Should the PWM output sound weird, just muck around with the pwm trimpot until it sounds normal. Same thing with the sine or triangle output, just adjust the tri off trimpot.

I've included the simulations I created on LTSpice; VCO contains the full circuit, PWM just the pwm section.

Needed is how many I personally need :)

Heres the links to the CAD source, Onshape: Panel source

• hardware/
  • bom/ - BOM Files (CSV and LibreOffice Calc)
  • cad/ - CAD Files
    • render/ - Files for rendering (inc. gltf models)
  • ltspice/ - LTSpice electrical simulations
  • vco/ - KiCad files
    • lib/ - External libraries
    • production/ - Production files (Gerber, etc.)
• journals/
• zine/ - Zine page :)

Circuit design influenced by: Moritz Klein DIY VCO Series Falstad Diode Clipper