Raspberry Pi I2S to SPDIF Hat

Discussion in 'Digital: DACs, USB converters, decrapifiers' started by Michael Kelly, Apr 30, 2016.

  1. earnmyturns

    earnmyturns Smartest friend

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    Quick question: I'm using a high-quality BNC coax to connect the 502DAC to my Soekris dac1541. I didn't realize I could do AES, how would I do it and would it matter?

    I've not tried the 502DAC as a DAC, as I had the dac1541 already and I have a thing for R2R DACs :D But for someone starting to build a stand-alone system, the 502DAC is a great one-hat solution, for sure. When I have a bit more time, I'll assemble a full bill of materials and assembly instructions (what I can recall, that is) for my work system. It was a lot of fun to put together hardware and software, and the 502DAC has performed flawlessly all along, tolerating my poor manual coordination and lack of proper anti-static precautions.
     
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  2. zalive

    zalive Rando

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    Hi Michael,

    I got in my hands 502DAC Rev. P6. Bought it through Audiophonics reseller since im in EU. Originally what I thought I was buying was Rev. P4 because this is what they advertized on their web shop. I wanted P4 because of one particular comment related to comparing those two revisions when it comes to digi out but well...I'm primarily interested to use it as a digital source. First impressions are quite nice. Much better and much more natural sounding than stock Hifiberry Digi+ Pro in its stock form.

    Anyway I have couple of questions for you if you would be that kind to answer:

    1. Is Rev.P4 by any chance done the different way than other revisions, with WM8804 being in master mode, similar to 502DAC Pro implementation? And in any way, what is the main difference between P6 and P4 revisions?

    2. Can you specify the rise time duration of S/PDIF digital output square signal for 502DAC? I need this data to determine how short coax I can use for digital out - I'd like to use something as short as 0.5-0.6 m but still be safe from acquiring transport jitter because of signal reflections.

    Thanks in advance for your valuable answers!

    Cheers,
    Ivor
     
  3. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    Rev P6 uses the same architecture as P4. The WM8804 is the slave and the PCM5122 is the master. On P6 we added the ability to use the Taitien low noise clocks versus the NDK which at that time we could not find anywhere! As you noted a particular user commented that he thought the P6 with the Taitien clocks was inferior. We replaced his unit with a P4 using NDK clocks and have since then discontinued the P6. Not documenting this was an error in judgement on our part and we have gone back to P4 only.

    If however, you have a P6 and the sound quality is good, I am not surprised. It is likely the P6 you have is using the NDK clocks already. We only shipped a small number of P6 boards with the Taitien option. We have no issue with refunding anyone who has a P6 and is dissatisfied.

    As for the cable question, I will need to test. I am on the road today and won't be able to get back to this until tomorrow. Send me an email to [email protected] so I don't forget! :)

    Regards,
    Michael
     
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  4. Lateboomer

    Lateboomer Rando

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    I am still eagerly waiting for 502AES, is the project still on going ?

    Secondly , can 502dac shield be used with Up2 Board ? Since Up2 also has gpio pin that can work like Rpi's one.
     
    Last edited: Oct 6, 2018
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  5. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    As mentioned before in this thread, we decided against doing the 502AES at this time. The 502DAC digital section is very solid and seems to have what the vast majority of folks want. The external clock in and I2S over HDMI did not gather enough interest. Again, this is at this time. I do have a proto of the board that we have not yet tested and maybe I will change my mind! :)

    As for the UP board, I have no experience with it and can not offer any advice.

    Michael
     
  6. t3hwx9

    t3hwx9 Acquaintance

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    Same pin layout is not sufficient. You'll need the HiFiBerry DAC+ driver which is currently available as the Raspberry Pi device tree overlay. Up2 is an x86_64 device with a different way of handling binary drivers.
     
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  7. Lateboomer

    Lateboomer Rando

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    Thank you for the explanation . Anyway , I think there is great interest among us for 502AES. It is very easy to find out . Lol .

    It is because we are looking for state of an art and no hold bar Ethernet-to-spdif streamer with simplest design and almost all of us have external dac to play with . As long as the output has aes , bnc and a way to tap i2s I am happy camper. I mean to generate i2s over HDMI , I could use modules from audio-GD to do it.

    I hope may be one day I could see you coming out of a pcie card that output spdif and i2s and x86_64 streamer can use it. I know that is a big hope.
     
    Last edited: Oct 6, 2018
  8. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    As requested rising edge and falling edge of BNC output. Please note this is without a cable which will slow the dges down based on length and capacitance. Sorry for the poor quality. I don't know how to get these off my scope and was too lazy to dig into the manual. ;)

    rising edge

    falling edge


    Michael
     
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  9. zalive

    zalive Rando

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    Thanks Michael :)
    If I calculate this correctly, coax for 502DAC should not be shorter than 1m to avoid transport jitter.
     
  10. zalive

    zalive Rando

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    Or perhaps I'm too cautious...

    Propagation speed specification for the coax I'm using (Supra Trico) is 0.78*c, which gives propagation time of approx. 4.27 ns/m. And the impact of cable on the rise time (3.8ns as measured on your graph if I read it correctly?) should slow it down to approx. 4.8ns. Reflection has to travel back to the shield, and forth to the DAC, so I guess 0.5m is not safely long enough. However I have a 0.6m long Supra coax cable which prolongs propagation time to just over 5ns, which should still be fine as DAC should have sampled the transition by the time reflection arrives.

    Do I calculate this correctly?
     
    Last edited: Oct 12, 2018
  11. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    Sorry I never replied to this, but this is way too much math for me! I was used to doing this sort of thing back in my old high speed network engineering days, but those brain cells have since died off.

    Seriously, I am afraid you are on your own with this.


    Michael
     
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  12. solarflight

    solarflight Rando

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    Is there a new batch foreseen for the 502dac?
     
  13. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    We have been putting batches into the store on a pretty regular basis over the last six months. If it is currently not available, it will be within a week or two, as I know we are getting ready to build the previous pre-ordered batch.

    Once we finish building a batch, we can re-open the store for new orders. Leadtime has typically been anywhere from 2 to 4 weeks depending upon the availability of the parts. With the holidays coming up it is likely that orders placed for the next batch will be a little bit longer lead time.

    Cheers,
    Michael
     
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  14. HumanFly

    HumanFly Acquaintance

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    Hi Michael! Do you have plans to take things to the extreme? It seems that there is a market for 250dollar (and up) HATs.
    Imagine how good a 504DAC in that pricerange could sound. I`m still using the 502 exclusively and although I`m tempted by the competition a little bit, I don`t like how they handled the powersupply-side of things.
     
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  15. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    I agree. I have been playing around with a higher performance version, but I am not yet satisfied. Once I am finished I will make an announcement here.

    Michael
     
  16. Clemmaster

    Clemmaster Friend

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    I2S audio and WCLK/MCLK input/output please :D
     
  17. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    The 502DAC has an 8-pin header that provides direct access to the I2S bus and I2C.

    Michael
     
  18. Clemmaster

    Clemmaster Friend

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    I mean LVDS over HDMI, which is the solution chosen by many manufacturers. Of course, the pinout needs to be user definable.
     
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  19. Greg121986

    Greg121986 Almost "Made"

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    I would be super into a DDC that allows I2S output by HDMI. Think Singxer SU-1 RPi Hat. But better. :)
     
  20. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    We have done an internal board with I2S over HDMI along with standard digital out and isolated external clocking support. The dilemma is how to test the I2S over HDMI. I am loathe to spend money on a DAC that has that input, especially since the interface seems to be unique to each vendor.

    Are any of you willing to lend me a DAC so I can test it? I made the I2S over HDMI a small add on-board so I can change it for different DAC's if I know which ones folks want. The initial pinout is for the GD Audio spec.

    Michael

    3d renders of the design:

    [​IMG]

    [​IMG]

    [​IMG]
     

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