This is a modification of the original CXADC ClockGen at https://gitlab.com/wolfre/cxadc-clock-generator-audio-adc

• Cost reduction: The main board PCB and the Si5351A is not necessary for this mod.
• Alternative use cases: Nearly any combination of the Domesday Duplicator, CXADC cards, and this build works.
• Simplicity: Some niche use cases were cut.

There are several changes that make this possible:

• The PCM1802 is configured in 512 division mode. This allows us to directly use a 40 MHz clock with it, while producing 78125 Hz sample rate recordings.
• USB configuration was edited to allow enough buffer for the higher sample rate recording, as well as remove alternative clocks.
• The Pi Pico is underclocked to 120 MHz. This allows a simple divisor for getting 40 MHz, without fractionals which introduce jitter.
• The RP2040 has a feature where you can output divided clocks on a certain set of GPIO pins. Using this, we output 40 MHz on GPIO 21.

• PCM1802 board (€4) AliExpress
• Raspberry Pi Pico (€2) AliExpress
• Wires
• Soldering setup (iron, solder, flux)

1. Enable 512 fs master mode by bridging MODE0

Unfortunately the most common PCM1802 board has a bug where the + side of the bridgable connections is not actually connected to 3V3. To fix this, you will need to add a cable.

2. Connect the PCM1802 board to the Pi Pico

• 5V to VBUS
• GND to GND (any)
• PDW to GPIO17
• DOUT to GPIO10
• BCK to GPIO11
• LRCK to GPIO12

3. Flash the firmware on the Pi Pico

Build and flash the contents of the firmware folder. Alternatively, you can use the prebuilt version to skip the building step.

1. Connect PCM1802's SCK to GPIO21
2. Build the necessary amount of clock generator adapters as in the original
3. Connect their GND to GND and their clock input to GPIO21

How you make the connection is up to you, but cutting an SMA cable may be a very easy solution if using the SMA version of the adapter boards.

1. Connect GNDs, connect PCM1802's SCK to the Domesday Duplicator's pin 40

1. Connect the SMA clock output of the MISRC to SCK and GND of the PCM1802

Use the AUX pins and pcm_extract instead.