Eurorack EngrEDU VCO 1

Introduction

The goal with this project is to provide a reference design to enable students to build their own Eurorack modules. It is a collaboration effort with my collegue and friend Professor Michael Schulze from the Lamont School of Music at DU.

Design Stage

The module used as reference project was a Voltage Control Oscillator (VCO) with several output waveforms that could be mixed and controlled externally.

Electronic Druid website has several CEM3340 VCO (Voltage Controlled Oscillator) designs. We took the original CEM3340 VCO and modified to include more features.

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

Prototype Stage

After getting an idea of the desired functionalities and the input and outputs of the system, we built the prototype on protoboards. This is an important step to make sure that the design choices make sense and work.

Reference Designs

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

PCB Design

The PCB design stage is done in concurrency with the prototype stage. With that in mind, as we design the PCB, we used Fusion 360 and KiCad to model the board and get an idea of the final product.

We decided to have an eurorack module with two PCBs and one panel board.

PCB A: has all the components that connect and show up on the panel board, such as potentiometers, audio jack connectors, buttons, switches and LEDs.
PCB B: has the VCO, mixing stage components, eurorack power connector, and additional components required for the board to function properly.
Panel Board: instead of using the tradditional metal plates, we designed the board in KiCad and manufactured the panel as a PCB.

PCB A

Specs

Inputs

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

Outputs

Sine
Triangle
Pulse
Ramp
Square
Mix Out

Schematics (Zoom)

Layout (Zoom)

3D Rendering

Interactive BOM (Link)

PCB B

Schematics (Zoom)

Layout (Zoom)

3D Rendering

Interactive BOM (Link)

Panel Board

Layout

3D Rendering

Overall 3D Model

Assemble Stage

The boards were manufactured by JLCPCB.

Assembled in house.

Testing Stage

Testing setup

The EngrEDU VCO 3340 is attached to the TipTop audio Eurorack and it is powered by the TipTop audio uZeus
Oscilloscope: Keysight MSOX3012T – 100MHz @ 5GSa/s
All waveforms were tested and plotted using the oscilloscope. The graphs will show peak to peak, maximum and minimum voltage.