Raspberry Pi I2S to SPDIF Hat

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

  1. Scott Kramer

    Scott Kramer Friend

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    Did the pics for you guys, since there were none yet -- was just at the keyboard when Michael asked for testers thru email, honestly thought I missed it so much time went by after that. Also can tone down the pics if they are annoying :)


    Will focus on testing 502 BNC vs Digi+PRO BNC (and some other spdif sources) -- to not muck up results with my special f'in snowflake schiit i2s

    Then on to testing the Kali/502(BNC,I2S)/Digi+PRO(BNC,I2S) (and a few other things)
     
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    Last edited: Feb 16, 2017
  2. pandather

    pandather Acquaintance

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    Just got mine in the mail too, setting up my Pi now! Thank you Michael. :) I have a diy external PSU so I can try to test LPS->Pi2->502 vs phone charger -> Pi2 & LPS->502. I'll be using a NAS to load the files from, with the only thing plugged in being ethernet. I just ordered a male BNC to female RCA adapter so I can use that instead of optical to communicate with my Modi Multibit.
     
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  3. Jeffjazzer

    Jeffjazzer Rando

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    Actually love the pics Scott Kramer. My sarcasm was kicking in heavily!
    Looking forward to hearing from all the 502dac testers. Thanks to all the inmates for the great info.
    Happy listening!
     
  4. noise11

    noise11 Rando

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    Hey guys, please report how 502dac sounds compared to digi+, also I have a question that maybe one of you have an answer, how much better is the SQ when Pi and Hat are fed by different power supplies instead of one (ps) feeding both(pi+hat)?.
     
    Last edited: Feb 17, 2017
  5. haywood

    haywood Friend

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    My 502DAC came as well, I'd like to add my thanks to Michael for the opportunity to test this bad boy out. After some brief MacGuyvering of the el cheapo case and some build flashing tomfoolery due to missing the post where Michael said you can just choose the DAC+ Pro during configuration it's up. Unfortunately it seems to have come with a case of the dreaded Scott Kramer high pitched whine disease which as far as I can tell is limited to just the physical board itself. I'll run it over the weekend to give the old burn in magic some time to banish any gremlins but if it's still there Monday I'll ship the Pi and all over to Michael to see what he thinks.

    This is using a smps so cleaner power might help, but my lps is still in transit. It's similar to the noise you get from the Pi audio jack in that it's a reflection of activity so largely muted when music is playing. Of course in between tracks is when things get quiet and the Pi is doing the kinds of things like heavy network activity that cause the noise. Adjusting the file preload and audio buffer to be on the small side helps mask the effect. Music sourced from nas has more noise than with usb (but that's probably just a reflection of one being faster so it's over more quickly). It's probably also worth mentioning that we're mostly running these boards open to the world, so there's no box to reduce noise. Putting a sweatshirt on top of the Pi solves the problem but then it'd probably catch fire.
     
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  6. Scott Kramer

    Scott Kramer Friend

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    Hi @Vastx

    Meant to check this out for you earlier. Hoping it would be some simple jumpers, but there is a conflict.

    Here's how the the Digi+PRO is setup and how it's driver selects clocks by GPIO:

    GPIO5 = select 22Mhz
    GPIO6 = select 24Mhz

    So I mocked up what you have to do to get the SPD2 to work with the Digi+PRO driver (Then you can run the board on anything you'd like piCore, MooDe)


    Pretend the Digi+PRO here is the SPD2

    Used a ZERO because the pins are not there (to illustrate)

    pi GPIO5 -> spd2 GPIO6 (red wire)
    pi GPIO6 -> spd2 GPIO7 (yellow)

    On the pi2/3 you will have to bend the pins, or remove them to make the connections. If you do not GPIO5/6/7 would be shorted together.

    IMG_0838.JPG
     
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    Last edited: Feb 17, 2017
  7. haywood

    haywood Friend

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    Just a quick update that the high-pitched noise is still there but maybe a little less obvious now. Or my brain is slowly learning to ignore that pitch. And I found an old rubbery iPod touch case someone gave me back in the day that kinda fits on top of the hat and squelches a lot of it. Plus I banished it to live on top of my sub on the floor. I don't think this is indicative of a design flaw, it could be something specific to this particular Pi, and I should probably mention that I'm pretty sensitive to this kind of noise, hate light dimmers and can sometimes relate to Chuck McGill.

    Anyway I think I can still compare it fairly so I ordered a new bnc to rca cable (because an adaptor would bug me, not judging anyone else) and will be pitting the optical and bncrca frankencable against each other as well as against a gustard u12 ddc (which is inoffensive but also kind of bland) and then the gustard with my mbp running audirvana. My lps probably won't get here until March so I'll be using smps and then update if it's an omg difference.
     
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  8. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    Guys,

    Remind me who is getting a unit and has an XLR input for testing?

    Cheers,
    Michael
     
  9. Lasollor

    Lasollor Friend

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    Hi Michael!
    I have an XLR input for testing.
    By the way I think my unit arrived yesterday, but I won't be won't be able to get it until the day after tomorrow.
     
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  10. darkstar>eyesoftheworld

    darkstar>eyesoftheworld Rando

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    Mine is coming today. I will be testing the XLR
     
  11. IceUul

    IceUul Friend

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    I am looking for hat with female XLR output, i understand production version will get male xlr output? How it is possible to get one?
     
  12. t3hwx9

    t3hwx9 Acquaintance

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    I'll be able to test XLR (although, my demo unit is in transit due to parcel-forwarding routine. ETA 5-7 days)

    @IceUul , AFAIK, production version will get TRS (because of a smaller footprint) and TRS→male XLR adapter. There are pre-made TRS → female XLR adapters available as well.
     
  13. IceUul

    IceUul Friend

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    Why i would want TRS? I need correct 110ohm AES/EBU XLR output, preferably female, since i already ordered the specific cable for it.
     
  14. Vastx

    Vastx Facebook Friend

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    Thank you so much Scott!!! I've been trying to figure it out but wasn't sure at all. I owe you one :D
     
  15. Scott Kramer

    Scott Kramer Friend

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    You're welcome. Now I'll be really curious if it works or not!
     
  16. Scott Kramer

    Scott Kramer Friend

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    @Michael Kelly

    The dreaded whine is on the P2 (same as P1), it really seems like it started a day after it was running. Thought I was developing tinnitus... ugh! Maybe you have a problem with the board layers, torque the board or press on it, it minimizes it, changes the frequency... gonna have to snap these in half!

    Really surprised this isn't bleeding into your spdif perf measurements... maybe it's before the regulators & filters?

    This is *not* in the music... it's the physical board making the noise in a quiet room.


    Same problem here.
     
    Last edited: Feb 21, 2017
  17. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    I wish I had an answer. Unfortunately my testing lab is not that quiet. But tomorrow I will fire the board up and see or hear what happens. Mind you my nearly 60-year-old ears may not even hear it, but I have a young person around who might.

    Cheers,
    Michael
     
    Last edited: Feb 21, 2017
  18. Scott Kramer

    Scott Kramer Friend

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    Cool, I think you'll have to solve it-- If they all do it you may get complaints. It isn't loud, but it is like something going bad in an old lcd tv or fluorescent ballast etc.
     
    Last edited: Feb 21, 2017
  19. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    So far only two have shown up. Which curious is it there are no switching inductors on the board, which is usually the source of that kind of sound. After the next build I will have somebody (probably my 17 yr old son) come in and listen to all of them with all my test equipment turned off.

    Cheers,
    Michael
     
    Last edited: Feb 22, 2017
  20. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    The TRS will not interfere with the impedance, it will still be 110 ohm based on the termination on the board.

    Cheers,
    Michael
     

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