Eurorack EngrEDU VCO 1

Eurorack VCO 1 (Version 1.0)

Electronic Druid website has several CEM3340 VCO (Voltage Controlled Oscillator) designs.

The original CEM3340 VCO was used as a start and modified to include more features.

The circuit is compatible with eurorack modules (+/- 12V).

After getting an idea on the desired functionalities, input and outputs, the circuit was built on protoboards.

Reference Designs

  • Skull and Circuits: VCO-1 – The Oscillator One (Link)
  • Kassutronics: VCO 3340 (Link)
  • Look Mum No Computer: CEM 3340 (Link)

3D Model

During design stage, Fusion 360 and KiCad were used to model the board and get an idea on how the board would look like.

This module has 2 PCB boards (PCB A and PCB B) and 1 Panel board.

Panel Board


  • 2 voltage/octave
  • Exponential FM
  • Linear FM
  • PWM
  • Sync (Hard and Soft)
  • Fine
  • Coarse (Frequency)


  • Sine
  • Triangle
  • Pulse
  • Ramp
  • Square
  • Mix Out



Interactive HTML BOM - PCB A



Interactive HTML BOM - PCB B

The boards were manufactured by JLCPCB.

Assembled in house.

Testing setup

Sine Wave

Triangle Wave

Pulse Wave - 0% PWM

Pulse Wave - 50% PWM

Pulse Wave - 100% PWM

Sawtooth Wave

Square Wave

Mix Out - All Waves Off

Mix Out - Square Wave

Mix Out - Triangle Wave

Mix Out - Sine Wave

Mix Out - Pulse Wave - 0% PWM

Mix Out - Pulse Wave - 50% PWM

Mix Out - Pulse Wave - 100% PWM

Mix Out - Sawtooth Wave

Mix Out - Random Wave

Mix Out - "Maximum" Wave

Sound Test 1

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