Raspberry Pi I2S to SPDIF Hat

Michael, sorry if I missed this earlier, but are you still planning on releasing a digital output-only card, without the DAC? Thanks!

 

No. For us the economics of supporting multiple cards at lower prices does not work. Adding the analog DAC also gave us a way to support multiple clocks for the digital section without the need for two cards and two drivers. I am quite sure for many folks the Digi+ or the DAC+ Pro are a better fit price wise.

Cheers,
Michael

 

Thanks Michael! I appreciate the response.

 

I don't think the price is a huge consideration in the audiophile scene, that was more for the broader Pi marketplace where cost is a much bigger concern. People here are more interested in getting the best possible performance and seem unsure about how the switch to the 502dac model might have affected that.

The power pins on the new version sounds like a great idea for anyone building an all-in-one. After reading some reviews I'm curious about how the iFi smps compares to a decent lps, but even then it'd probably be nicer to use the pins and wire a power plug into the back of a case unless you have the Pi tucked away out of sight.

 

It is my firm belief that for digital out you will not be able to tell any difference between any external supply and the on-board LT3042. For analog however, there could very well be a benefit to running the shield from an LPS and the PI from it's own supply, possibly even another LPS.

I just finished designing our own LPS using a toroid and the Walt Jung Super Regulator with some tweaks. Initially the need is for our sister company, MJK Audio, to use with our DAC/AMP with tube headphone amplifier. In that use it will be set for 24V@2A output. But the design is flexible and with a different toroid we could do 5V. It's a bit overkill for the 502DAC, but it will allow us to test what difference a low noise (simulation says <4uv) supply will make.

We will keep you posted on this issue.

Cheers,
Michael

 

There's definitely not a huge difference. Even so unless you were really on a budget I'd probably recommend something like the iFi one as it seems to test much better than a typical smps and you need to get one anyway.

Cool, will be interested in hearing what you think / measure. The flavor of the month in audio seems to be clean power so your timing is perfect if you can get a product that offers a range of outputs (not like 5-20v but options with 5, 9, 12, etc.) shipping soonish.

 

The iFi is supposed to have 1uV of noise in the audio band... It tests better than most cheap LPS too. There be links somewhere, let me dig it up.

Edit: Finally remembered the keywords to use: http://www.audiocircle.com/index.php?topic=149059.0

 

Yeah. I set it up using the Hifiberry Dac+ settings from the DietPi config and installed ALSA utils. I haven't had time yet to do any serious listening but that's next

 

@Michael Kelly I don't want go off topic, but I wonder if it possible to build up a HAT dac in the very state of the art league. The possibility of sending i2s output to dac without the interposition of LVDS transmitter and receiver seems to be, theorically, the way to go to get the best results. Why no one, as far as I know, use the best of the chips ( say top Wolfson, last Sabre....) in HAT dacs?. It's a technological problem ( the board is small) or a marketing one or other? It is not my business but I think that better clocks and better dac chips sum in the order of tens $, leaving - if the results are so much better - large gain margin to maker ( I think a lot of people is willing to pay in the range 500 -1000$ for really good dac)
Thanks
Marco

 

It's quite a challenge to make a DAC on the Pi due to the intense noise the Pi radiates. Getting the analog noise floor much below 100db is very challenging. Never mind the -110 to -120db you would need in order to compete as a top end device. In the digital domain this is not a problem. Keeping clock jitter low and your output levels strong is really all you need to do. The I2S data sent as SPDIF over XLR, BNC or even opto, is a very good way to separate the digital from analog. As long as all the bits are recreated with a clean clock, you have 100% accuracy.

Still, you are right that it would be nice to have it all in one box. We are experimenting with a board using the Pi 3 Compute Module and a shield/hat location next to it. This should greatly reduce the noise coupling between the Pi and a DAC Hat. FOr us, this design has other, non-audio uses so it won;t be a loss if the noise is not much better.

Below is some renderings of the design. We are just now testing the protos. Once that's going well we will go ahead and have the box fabbed.


Front view with 2x16 LCD and rotary encoder



Rear view with 502DAC add-on


Interior View showing Compute Module, mSATA storage, WiFi, optional USB Cell modem, 502DAC shield and proto area

As I said, this design has primary use for embedded and as such we already have two customer for it (adding custom interface circuitry where the proto area is now). Still we think it can serve as a very good network audio streamer and DAC (if we get that noise low enough). For embedded use we will supply it with a low cost 24V switcher. For analog audio we will use our new LPS design we're also testing.

Cheers,
Michael

 

Thanks for the thorough and comprehensive explanation....pending the development of your future dac streamer
Marco

 

I think I just ordered the last one of the HAT boards. Sorry if this has been covered before, but is there a case that RPi + HAT will fit into in order to avoid having a naked RPi lying about?

 

On my side i wish you just sold a "streamer" cause I'm not comfortable enough configuring PI. Would just plug it into my screen, put some music's into it and voila. I guess I'll think on the next batch and re-read the thread back to front.

The DAC part isn't important, i already have a Bifrost Multibit and a NAD M51 (which I use much more).

That said this has been an interesting reading, keep up the good work.

 

From Chicago Electronics. Supplied screws are too short for the 2 extra spacers that I used, thus the elastic bands. You will have to trim the spacers to match the outputs and dremel out protrusions inside. Easy enough to do. Inexpensive and temporary until something better comes along. Different colors too
https://chicagodist.com/collections...oducts/cyntech-raspberry-pi-b-plus-case-clear

 

Has anyone gotten a printed case or if you made something to accommodate the hat/pi could you post pics?

 

I just ordered two of these and two of the clear spaces. Once we get them I'll see what size screw is needed. Maybe this is something we can supply. I am concerned though that the company only had two of the clear spacers in stock. Not sure about other colors. I'll check with them once I determined this is a reasonable option.

Thanks for the find and photos. Well done!

Cheers,
Michael

 

Just a quick reminder, the 3D .step model for the board is on our web site at:

http://www.pi2design.com/uploads/4/8/5/3/48531975/502dac_step_p3.zip

Cheers,
Michael

 

In the uk/europe you can buy it here:
https://shop.cyntech.co.uk/products/raspberry-pi-case-model-b-compatible?variant=843166349

 

502DAC impressions

First I'd like to thank Michael Kelly for sending me a 502DAC test unit. I've spent the past few weeks listening to it with different setups.

Conclusion:
Its a solid board, with great sound quality and cost/performance ratio. Versatile. Definitely a keeper.

setup used: Power iFi iPower-RPI3-502DAC-Yggdrasil-Jotunheim/Vali2/Teac HA-501

Digital output
The AES output sounds a little bit cleaner with more articulated bass than the BNC, but it might be the better AES implementation on the Yggdrasil.

Compared to the Digi + Pro, they are more similar than not. BNC and AES sounds a little bit cleaner with better instrument separation than SPIDF on the Digi+ Pro.

I couldn't really tell the difference between Digi+ Pro BNC (soldering needed) and 502DAC BNC, but again I preferred the AES/EBU connection to both.
The fully balanced chain (502DAC AES->Yggdrasil->Jot->HD650) opened up the Jotunheim, with more details, better imaging and focus.

Analog output
The sound quality from the analog output is ok, sounds bad compared to the Yggdrasil, sounds good compared to the iPhone or Macbook headphone out.
I think that a RPi/502DAC, with a usb drive and somethng like a Vali2 would make a good upgradeable starting rig. Then you can save up for a dac of your choice, a NAS, subscribe to Roon etc., there will aways be a place for the 502DAC in the chain.

Software
piCorePlayer, Volumio 2 and Rune Audio's newest beta works when you choose Hifiberry Dac+, but for some reason Volumio 2's interface had a small lag just enough to became annoying really quickly. (It had the lag with the Digi+ Pro too so it's unrelated to the 502DAC)
I've also registered a trial account with Roon, to try the 502DAC as a Roon endpoint. It was very fast to set up, basically plug and play and "just worked".

My only complaint is that its hard to find a nice case for it, more so if you use the XLR adapter.
For a quick DIY solution an iPhone 6s case is just big enough that the adapter won't protrude, but it is ugly. For now I'm using a decoration box I've found in a local shop.

 

Guys, see this on the Hifiberry site:

https://www.hifiberry.com/shop/boards/hifiberry-dac-pro-xlr/

I know some of you believe that the 1/4" to XLR adapter must somehow affect the sound, so this might be a good alternative. It is not isolated, and has only XLR, but for those who need this it should be a good choice.

Cheers,
Michael