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 :

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 :

Layout :

Delivery by JLCPCB :