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PI2AES Digital Audio Shield for the Raspberry PI

Michael Kelly

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#1
Folks,
We have just finished testing the protos of our new digital audio shield. This replaces our 502DAC for digital audio out. This unit has the following features:

Woflson WM8804 AES Transmitter with dual NDK Low Noise Clocks
SPDIF COAX via RCA
SPDIF Optical
AES Balanced via XLR
Direct Buffered I2S via Header, with I2C, 5V and VIN Power
LVDS Differential I2S via HDMI with support for Gustard or PS Audio pinout (selected at time of order)
Single 12V to 48V input, with on-board [email protected] supply
Separate Ultra low noise LDO's for WM8804 and NDK Clocks

Below is a photo of the unit.



Test results and comparisons to 502DAC. Note that the 502DAC board I have here on the bench has a broken XLR. Once I get another in hand I'll add that test. I can't even keep a unit for myself since we are always back ordered!

502DAC BNC. This is what everyone has been very happy with, yet clearly there was room for improvement.



PI2AES RCA. Noticeably better than 502DAC BNC.



502DAC OPTO Jitter. Yikes!



PI2AES OPTO Jitter. Huge improvement over 502DAC Opto, but still not as good as P2AES RCA





PI2AES XLR Jitter. Note that the results seem to be a bit worse then the PI2AES RCA. But XLR is needed for long cable runs or interfacing with pro audio equipment.


Cheers,
Michael
 

Michael Kelly

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#3
Good job, Michael! Thanks for sharing your results.
From your lips to Amir’s ears! Maybe he’ll promote me to the front page? Hint, hint.....

I’ll be linking to the data sheet and hw reference manual sometime this week.

Michael
 
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#5
Looks great!

Congrats on the new release.

When are you going to list it and when do you expect to ship?
 

Michael Kelly

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#6
The plan is to have them ready for limited production by the end of May. We also made a change to add a BNC output. To do this we had to move the speed LED's to the side of the board. Here are a couple of 3D captures of the final revision:

pi2aes_top_p2.PNG


pi2aes_front_p2.PNG
 
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#7
Any power supply recommendations for this hat?

When are you gonna start taking cash?

I'm still interested in this puppy.
 

Michael Kelly

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#8
Prototypes are complete and testing has gone very well. We have bought enough parts to build an initial 25 units. Price will be $129 w/o case, acrylic case (like our 502DAC Case) will be $15. As for power supply we will offer a basic [email protected] switching supply, but you can get your own if you want.

Michael
 
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#11
@Michael Kelly Have you compared the new hat to your old when it comes to sound quality?

I saw on another forum that you have a digione sig.. Have you compared the pi2aes to that?

The last question, I also see you are gonna sell a few next tues. Will you have power and the cases too?
 

Michael Kelly

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#12
I did a measurement of the digital jitter from the Allo Digi One Signature. The results are shown below. As for listening tests, I have not. I do not consider my ears to be good enough for what are very subtle differences as measured. For cases I will have a clear acrylic case similar to the one we sell for our 502DAC. And a 24V Switching Power Supply.

ALLO Digi One Signature, RCA Output

allo_sig_rca_clean_pwr.PNG

PI2AES RCA again for comparison:

aes_jitter_bnc.PNG


Michael
 

Michael Kelly

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#14
We only had the Digione Signature loaned to us by a friend. Comparison testing is not something we will normally do. That is what is great about what folks like Amir provide!
 

Michael Kelly

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#18
After initial testing, I have decided to change the LDO devices on this board to the LT3042 from analog devices. It is more expensive than the ones that we had, but the noise levels are significantly lower. The ones I had chosen are very good devices, but I may have been mistaken in what effect they would have. Although I’ve been pleased with the measured results, the handful of folks that have done some listening test for me are not as convinced as the measurements might indicate.

As always, accurate thd, noise and other measurements are very necessary as a baseline starting point, but since everyone’s ears and musical tastes are so varied, listening still remains as the final deciding factor.

This will delay the initial rollout by about three weeks, pushing us to the end of the month into the beginning of July. I will continue to post updates as they come along.
 
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#19
Dear Michael,

As you mentioned, i am one of the lucky guy, who get PI2AES from you, for listening test. I am already express my very first impression to you, and just want to repeat here... CONGRATULATIONS!
I see people start to ask for listening impression and comparison. My full review will be ready soon, but if you don't mind i would like to point here some observations to start practical dissuasion, which eventually will be interesting for all and also for you. Please tell me if you agree..
Here is what I am doing last few days already and just can't stop )

I have Allo Digione, Allo Digione SIgnature, DAC502 and PI2AES for AB comparison..


And here different DAC that I am testing with PI2AES


As I say full details is coming, but you JUST DID IT. It's amazing! Thank you so much from me (and eventually for all of us). Complements.

Coming back to test.. I see you already did small changes ( LDO devices, LT3042). Is it already in the prototype I have? I just so curious.
Also regarding power supply.. First I connected PI2AES to 12V switching PSs i had around. In configuration where PI2AES and RPi was powered from the 12V. In this configuration sound was not good. But after I used simple 12V lead-acid battery (12V 6Ah), it's change everything. It has sound I never ever heard before in my life. And this is what I had experienced up to now as digital sources..
FiiO X3, X5, X5III (USB) - coax out, HiBy (USB), Colorffly C4 (coax) Mojo (Poly), Gustard U12 (USB- AES…), Topping D10, Singxer SU-1, Melodious Audio MX-U8, Allo Digione, Allo Digione SIgnature, DAC502.
Non of them sound to me as PI2AES. It's whole new story now. I just go thorough well know songs, album by album and cant believe how different and realistically they sound now. So exited to hear first impressions when it goes to production and reach all of us..

So my massage to other testers and eventual users... before invest to power supply, you may try just standard 12V lead-acid battery first. Amazing sound-stage! And apparently on board power conversions you designed and implemented works extremely well if good stable 12V DC provided.
Something like this..



Some question for you I have at the moment:
do you think it worth to try 24V battery? Is higher voltage may further improve sound? Or 12V is good enough?
Also which configuration you would suggest, 12V to power both (PI2AES+RPi), as I am doing now. Or separately power 12V-PI2AES and 5V standard adapter for RPi? What is better and optimal from your point of view.
Thank you so much.
 
Last edited:

Michael Kelly

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#20
Wow! First let me say thank you so much for the kind words and excellent work in doing the review. I look forward to the final report!

To answer your question about availability, the final version is being built next week, though in limited quantities to make sure everything is ironed out. As one of our testers we will obviously provide a unit to you to allow you to update your review. We are also hoping that Aamir (wink, wink) will also be interested in reviewing for this website.

For power supplies obviously a high-quality linear or the battery power as you have seen does provide the best performance. The problem of course is the practicality of running it from a battery which then will eventually discharge and need charging or replacing. Can I ask if you have a sense of what was not optimal with the switching power supply? Perhaps it is a matter of degree and can be workable for others.

The new version uses the LT3042 for the internal LDO rails and hopefully that will reduce or illuminate the loss of sound quality when using a switcher.

In any case again, let me thank you for your work and this is why we build these products and hopefully you can inspire folks to enjoy their music catalog all over again!
 
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