USB 2.0 Multichannel DAC Project
This project is in a pretty early design stage, but some things are already moving forward. See previous versions here: [v01]
- 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.
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.