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USB 2.0 Multichannel DAC Project

About

This project is in a pretty early design stage, but some things are already moving forward. See previous versions here: [v01]

Design Goals

  • Must offer USB 2.0 high speed compliant audio device so no driver is needed under linux
  • Sample rates above 48kHz must be possible, ideally 192kHz and 24bit sample depth would be very desireable.
  • Multichannel design. For the moment i need at least 4 output channels but the board should easily be upgradeable to 6 or 8 channels
  • A resampling DAC chip with a very good PLL is required as well as a low-noise DAC clock oscillator OR in case of a very cleanly clocked I2S source we can go NOS-DAC (no oversampling).
  • Low noise external power supply should be considered as USB bus power will always be pretty dirty. Maybe powering the USB->I2S converter with USB bus power is a good idea though as we will spare some components and can completely isolate these power rails.

Chips in the current design

The Amanero USB to I2S solution uses an ATMEL microcontroller and a CPLD together with three (!) low phase noise crystal oscillators. This should have a very clean I2S output. With the available firmware update it can handle two I2S outputs, thus being able to output four channels of mono audio.

As I always wanted to build a DAC with Texas Instruments' flagship DAC chip I chose to go with the PCM1794A. Please see attached images for a first schematic and PCB design. This will very likely get redrawn in KiCad once I get the hang of it :)
The Images below show only a stereo portion of the DAC, it will be doubled or tripled for the desired chnnel count of course.

Images:

Files:

Name Size Type
test4_pcm1794.T3000 406.8 KB application/octet-stream