Request for Design Review My High-End, Open-Source DAC

Electronics
1

Hey, folks!

I decided I wanted to design a really nice DAC that can be made (relatively) cheaply, and fit inside a Framework expansion card, among other things.

my_dac.pdf (502.6 KB)

The design is open-source, and I would greatly appreciate folks’ feedback! I am most interested in possible issues that I did not foresee, making this cheaper, improving its performance, as well as feedback on my requirements themselves:

Draft Requirements

The DAC must perform competitively with other top-of-the-line audio solutions:

  • The PCB must be at least 4 layers, including ground and power planes, to minimize crosstalk between channels
  • The DAC must support audio at 8.000kHz, 11.025kHz, 16.000kHz, 22.050kHz, 44.100kHz, 48.000kHz, 88.200kHz, 96.000kHz, 176.400kHz, 192.000kHz, 352.800kHz, 384.000kHz, 768.000kHZ
    • Note: 768kHz is important, as some high-end consumers claim that they can hear the difference, and high-end products tend to have this feature
  • THD+N must be below -120dB from 20Hz+
  • Intra-channel phase shift must be 0. degrees from 0Hz to 20kHz and there must be no measurable inter-channel phase shift
  • Frequency response must be flat below 20kHz, rolling off not before 20kHz
  • The output must be capable of swinging 10V p-p, and should do more if there is space on the board for additional OpAmps on the output stage.
  • Current-limiting on the analog rail (which must occur due to USB-PD constraints on many devices) must not affect these specs

The DAC must be cost-competitive at low volumes:

  • The design will be manufactured at JLCPCB, and should take advantage of suppliers like LCSC and the cost-effective chips that they supply where they meet the requirements above
  • The XU316 MCU must not be replaced, as it comes with a free reference software USB audio stack implementation that is known to support 768kHz USB audio with minor modifications
    Initially, optimize cost for small batches of ~5 PCBs at a time

The debug interface on the MCU sheet must be easily removable if required to meet space constraints, ideally reattachable, though snap-off is acceptable.

The DAC must physically fit into a Framework expansion card. See the FrameworkComputer GitHub. I am not allowed to link it here as there is a post limit on links.

If interested, go ahead and review the design in more detail: GitHub - rothn/compact-hd-dac: A compact, HD DAC

  • LTSpice simulations of selected analog circuits in root directory
  • KiCad v9.0.7 schematics in “dac_board” subdirectory
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