A 4 channels DAC for the EuroPi

This is a custom PCB that add a four channels DAC to the EuroPi.

The DAC is a MCP4728 :

  • 12-Bit Resolution
  • 4 Buffered Voltage Outputs
  • Single-Supply Operation: 2.7V to 5.5V
  • On-Board Non-Volatile Memory (EEPROM)
  • Normal or Power-Down Mode
  • Internal or External Voltage Reference Selection
  • Rail-to-Rail Output
  • Low Power Consumption
  • ±0.2 LSB DNL (typical)
  • Address bits: User Programmable toEEPROM
  • Standard (100 kbps), Fast (400 kbps) and High Speed (3.4 Mbps) Modes

The voltage reference is a LM4040, 3.0V.

The DAC outputs are connected to the EuroPi 3, 4, 5 and 6 outputs as follows :

EuroPi output DAC channel
1
2
3 D
4 B
5 C
6 A

This specific order of the channels was chosen to facilitate the PCB routing.

The EuroPi outputs 1 and 2 do not change and are still driven with a PWM output from the Pico.

Power supply :

This custom PCB swaps the 10-pin Eurorack power connector for a 16-pin one and removes the onboard power regulator, opting to use the 5V directly from the Eurorack power supply instead.

Schematic :

Here is the schematic of this PCB : dac-board-v2.1.pdf

Project files :

github.com/francoisgeorgy/europi-dac

Why build this custom PCB?

This PCB project was mainly a fun excuse to experiment and learn:

  • KiCad practice: a good opportunity to get better at PCB design.
  • SMD assembly with JLCPCB: tried out having the board made and assembled by an external provider.
  • Eurorack power filtering: played around with filtering power right on the PCB.
  • DAC vs PWM outputs: wanted to see if DAC outputs really outperform PWM for basic CV voltages.
  • Just for fun: because DIY projects are always more fun!

Assembly :

Europi-DAC-3D.png

Europi-DAC-3D-2.png

Layout :

Europi-DAC-PCB-front.png

Europi-DAC-PCB-back.png

Delivery by JLCPCB :

Europi-DAC-assembled-pcb.jpg