IAN CANADA TRANSPORTPI DIGI III Digital Audio Interface Module

The Ian Canada TransportPi Digi III is a digital transport interface designed to turn a Raspberry Pi into an audio source and deliver reclocked signals to an external DAC. Its four outputs, isolated coaxial RCA S/PDIF, optical, I2S over HDMI and I2S over GPIO, rely on dedicated reclocking for each format, while the architecture supports PCM streams up to 192kHz.

To reduce jitter, the circuit uses three discrete 1-bit reclocking stages for S/PDIF and two multi-bit stages for I²S over HDMI. Two FemtoMck oscillators of 45.1584 and 49.1520MHz are pre-installed on replaceable sockets compatible with FifoPi clocks; 22.5792 or 24.5760MHz clocks can also be used. The local MCLK output on a U.FL coaxial connector and compatibility with SinePi allow external clocks to be integrated, without requiring a FifoPi board for reclocking.

The Digi III improves the power supply with a low-noise, high-current LDO regulator, which can be bypassed, as well as filtering optimized with ultra-low ESR polymer capacitors. Its four-layer PCB dedicates two internal layers to shielding, while impedance control aims to preserve signal integrity; the direct 3.3V input makes it easy to use a battery or supercapacitor power supply. Finally, a compatible DAC can be mounted directly on top of the board, combining Raspberry Pi transport and digital-to-analog conversion in a compact configuration.