How to get direct i2s input to any Schiit DAC w/ USB card

Inspired by @Scott Kramer 's Modi Multibit i2s input thread here, I decided to see if I could do the same with the USB card headers on a Bifrost - which appear the same on the Gungnir and Yggdrasil as well.

Standard message: this didn't blow any of my Schiit up, but I would feel super bad if it did yours. So I would recommend against doing this. There are no user serviceable parts inside!

Anyway: This mod will allow you to use the USB input as a direct i2s input from, for instance, a Raspberry Pi based digital transport, such as a pi2design 502DAC or a HifiBerry Digi+ Pro.

But why? Well, this is the most superior input method available, to any DAC, as it bypasses the intermediate SPDIF/AES/USB/etc translation stage and allows your source to speak to your DAC in both of their native languages, so to speak.

Do keep in mind the following post from Scott about MCLK multiples:

The Modi Multibit uses the same DAC chip as the Bifrost, so the Digi+ Pro would be preferred when interfacing with both. Unknown re: the Gungnir Multibit and Yggdrasil, but I would err on the side of the Digi+ anyway (502DAC offers better performance and better connectivity, but D+Pro is cheaper and is a HAT instead of a Shield so fits in way more cases).

Moving on to the how, as images don't last forever:

Counting UP from the rear ports side of the board.

On the longer 14-pin header:
Pins 3, 5, 11 and 14 are all GND.
Pin 2 is +5V.
Pin 4 is +3.3V

The following pins need to be jumped to allow you to select the USB input:

Pin 1 needs +5V (Pin 2)
Pin 6 needs GND (Pin 5)
Pin 9 needs +3.3V (Pin 4)
Pin 13 needs 2.5V. I did this with a simple voltage divider - two resistors of equal value - one placed from Pin 13 to +5V (Pin 2), and one from Pin 13 to GND. It will also function jumped directly to 3.3V

The i2s input pins themselves are on the shorter 8-pin header:
Pins 1, 3, 5, and 7 are GND (one of these will need to be used)
Pin 2 is Master clock
Pin 4 is Bit clock
Pin 6 is Word clock
Pin 8 is Data

Please keep in mind that you should keep your i2s leads to your source as short as possible. While it would be a very elegant solution to rig up Ethernet jacks on both ends and use a (very) short patch cable, i2s was not designed to be used with cables, it was only designed to travel across a circuit board. Your i2s source needs to be sitting on or behind your DAC. There are ways to buffer the signal to drive it farther but that is outside the scope of this discussion.

Good luck and happy listening!

 

Nice @auri!

To be safe I'd put 10K current limiting resistors on the usb 5v/gnd, 3.3v/gnd, and cirrus disable... since it's still working probably ok but you never know... could be stressing those input pins. You can measure the current with the meter you have.

Did you come up with a nice way to connect the i2s?

 

Thanks for the input, I'll make a new BS board with those resistors just to be safe. Too easy not to.

The only reason I did this was to interface with my Bifrost Multibit, so I'm waiting on getting a Digi Pro seeing as how my 502DAC won't really work. I'll figure something out, esp now that finals are over!