Raspberry Pi I2S to SPDIF Hat

The Pi has 10/100 Ethernet and the 502dac has i2s out via a header but you'd have to make your own cable. Most people in the thread are using this for the spdif output but @Scott Kramer has a number of posts where he's using i2s with it.

 

If you want only i2s, I think Kali Reclocker from Allo Audio is more suitable than 502DAC. As excellent as 502DAC is when outputing AES/EBU and BNC, i2s output from 502DAC is basically raw Pi's i2s plus MCLK generated from PCM5122. Price of Kali reclocker is cheaper too.

 

Man this stuff is way over my head. Purchased a Pi 3B with hifiberry digi+ pro last night but will that board simply add on or I need to replace the Pi with Sparky?

 

Kali reclocker works with Pi 3, you don't need Sparky.

 

Remember, there are 2 modes the pi can operate in, master/slave. It's deceiving... but the i2s is actually being sent into* the pi (master mode), to perfectly align the PCM data with the i2s. That i2s with newly aligned PCM data is simultaneously driving the dac chip and wm8804 (i2s to spdiff conversion) on the 502DAC.

So it's not bad like raw pi i2s, where the division is wrong for the **44.1x multiple, actually mathematically generating jitter. And needing a PLL to recover the clocks, adding even more jitter.

*or a way to think of it, the pi is simultaneously listening on the i2s circuit.
**the pi only has a single 12MHz crystal, ok for the 48x, not 44.1x

The 502DAC and Digi+PRO operate in master mode.

I think you have a good starting point with pi3/digi+ pro.

 

I totally agree. The I2S header on our 502DAC was put in for internal testing and you would void the warranty if you connected to it. The signals are not protected from static or buffered in any way.

Cheers,
Michael

 

Lol, I gotta take a lof this on faith cause when trying to follow the processing in my mind my brain erupts with fireworks. I thought I understood it this way. Audio stream comes into the pi slave (via ethernet for me) and travels using i2s to the 502dac (master) grabbing the right clock along the way and driving the wm8804 for spdif conversion while still on the i2s highway. An aside, picoreplayer has a master/slave option fo the 502dac/pi. Not knowing what I am doing, I left it alone. There's probably a life lesson buried in here somewhere.

 

I tried a comparison as I said earlier (AKM 4495S vs PCM5122) and I heard the most notable differences on a solo piano song.

chain 1 AKM 4495S was: Dynaudio Xcite 12 - Rega Elex-R - Aune S16 DAC - spdif AES 502DAC (Rpi2, Moode 3.7 , TIDAL, LAN)
Results: more emotion, each note was distinct and resonated inside my brain and heart; each note had decay ant the whole song had more variation

chain 2 PCM5122 was: Dynaudio Xcite 12 - Rega Elex-R - RCA analog out 502DAC (Rpi2, Moode 3.7 , TIDAL, LAN)
Results: the notes mixed together and the emotion was less intense, the whole song souned more plain and equal

I had a few problems matching the volume from both outputs as the S16 has 2.8 V rms vs the 2V from the 502DAC

PS: My wife had the same impresions as I did, and she has more sensitive ears

Anyway on more crowded songs the differencies were harder to notice and I don't think the 700 USD price of the S16 worth the improvments.
Maybe for 150-200 USD yes would be a good upgrade.

Some pictures with my modified case (https://www.modmypi.com/raspberry-p...s-b-plus-2-and-3-cases/pi-dac-plus-case-clear)

 

@robyfow, if you very gently heat the edges of your new holes with a propane torch it will smooth them and get rid of the slightly jagged look.

(Might want to experiment on a scrap piece first.)

 

Fantastic write up, thanks! BTW, the AK4495S is quite a bit better than the PCM5122 for THD specification (-100 vs -93), and better still on the Signal to Noise Ratio or SNR (120db vs 112db). That likely explains the sense of "openness" you get with it. The really good news is the AK4490EQ is much, much better on THD (-112db vs. -100db) than the AK4495S, while still maintaining the excellent SNR of 120db. With the expectation that the AK4490EQ shield will be under $160 (just $70 more than the 502DAC) plus a world class headphone amp, I think the value will definitely be there.

Quick question on the case: Did you have to glue the pieces together? I use a PCB service in China called Elecrow. They offer an acrylic service that is pretty inexpensive and very good. I could put together a pattern for a case kit with all the right holes pretty easily, in fact does anyone know a good open source starting point? Are folks willing to put it together including gluing?

Cheers,
Michael

 

Are their many devices that accept I2S input? We do not make I2S available (except for test) and had not thought about it as a useful interface on it's own. I'd love to hear more about using direct I2S connections to other devices.

Cheers,
Michael

 

I just got the 502DAC and I am running with RPi2 and Volumio 2. I am powering with iFi iPower. I get the green light on the 502 DAC but not output via BNC to Gungnir Multibit. I previously had it working with Digi + and coax out. Any ideas or suggestions?

 

First make sure Volumio is set to use the Hifiberry DACPLUS. This is done under settings. If that's correct, then check the SPDIF and/or analog if possible. It also might be that the BNC pins were not trimmed to avoid contacting the USB shell of the Pi. If none of that works send an email to [email protected] and we'll work on getting a replacement.

Cheers,
Michael

 

Many modern DACs now come with I2S input using LVDS over HDMI transmission.
The problem is that multiple pinouts exist and you would need to make a configurable pinout to cover all of them (like the Singxer SU-1 or Audiobyte Hydra-Z).
The most common pinout is the PS-Audio, which Audio-gd and (I believe) Holo use, as well.
It'd be indeed awesome to have a HDMI I2S output on a shield like the 502!
Audio-gd and Audiophonics sell TTL to LVDS conversion boards, but having the HDMI port on the shield directly would be much better.

 

The case needs no glue for assembly
Here is a link with Pi-DAC+ ModMyPi Case Assembly Instructions, the black version, I have the transparent version but it's the same
https://www.modmypi.com/blog/pi-dac-plus-modmypi-case-assembly-instructions

 

To get the best results we still need an I2S master such as the WM8804 and the NDK clocks, so what about a shield that has XLR balanced out, Coax and I2S via HDMI connector? Or the same digital outputs as the 502DAC, but replace the LED's with a vertical HDMI connector? Like this:



Cheers,
Michael

 

It's quite challenging to get vertical HDMI working reliably and be strong enough to sustain the strain of plugging/unplugging.

I would give up one output just for having a flat HDMI connector.

Otherwise, yes, the scheme with WM8804, NDK clocks and master mode will be awesome.

 

I have used these on other projects successfully. The connector has four very robust tabs soldered into the PCB. Also note that it is mounted just in front of the mounting hole. Obviously you could still break it, but it will be virtually as strong as a horizontal part.

However, if the goal is buffered I2S what other interfaces even need be there? Using the WM8804 to create a set of very high quality I2S signals does not mean we have to use the SPDF output of the WM8804 for anything!

Cheers,
Michael

P.S. Found this reference for PS-Audio:

 

The idea behind these types of devices (in the broader non-Pi market anyway) seems to be to have enough port variation that you scoop up as big a chunk of the market as possible with one device (see Singxer SU-1 or whatever). Adding i2s would add an additional pool of audiophile type users to your potential uses base, and losing the toslink probably isn't too great a hardship for most people, but if you ressurrect the 502SPD it'll cannibalize sales of the 502DAC.

 

Yep, but upgrading the 502dac may make an oem sit up and take notice....