Raspberry Pi I2S to SPDIF Hat

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

  1. philipmorgan

    philipmorgan Member of the month

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    @Michael Kelly: I'm comfortable enough with the terminal and a text editor to experiment with getting this working on a Raspberry Pi 2 and Volumio, so count me in for that.

    EDIT: I should say Volumio 2 :)
     
    Last edited: May 1, 2016
  2. fraggler

    fraggler A Happy & Busy Life

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    I'm a completely new to the world of Raspberry hifi and will likely roll with Volumio2. I can be a test case for how dummy proof any loading and configuring instructions end up being. :)
     
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  3. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    OK guys, that's all great. So I have three crash test dummy's lined up! Now it's going to go a little bit quiet as I need to send out the design to be fabricated and then tested internally. I estimate about 3 to 4 weeks from now we should have some Proto's to send over.

    Cheers,
    Michael
     
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  4. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    Posted this in the tube amp thread by mistake!

    Quick question - Does anyone have interest in SPDIF in? The WM8004 has a SPDIF input that I am currently not using. If so, would Coax or Optical be more useful? Or both? With Coax what research I did seems to disagree as to whether or not it should be transformer isolated.
     
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  5. philipmorgan

    philipmorgan Member of the month

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    I don't currently have a use for that, but I'm curious what the use case(s) would be.
     
  6. IceUul

    IceUul Friend

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    Can anyone explain to me why this would be theoretically better than: Linear USB PSU 2.5A 5v -> Raspberry pi 3 -> Hifiberry Digi+ with transformer -> coax/spdif to DAC?

    I was just planning to get the setup above to run my vintage DAC's that does not have usb input. But now i am reading this here...
     
  7. Vastx

    Vastx Almost "Made"

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    If by this you are referring to the spdif hat designed by Micheal, it is very similar to the digi+, very similar. But it has been designed to maximize the performance: better voltage regulator, possibility to run external power, better clock(s). It has more potential than the digi+. Theoretically it SHOULD be better. But we won't know for sure until we have listened to it.

    You still would have to buy all the things you mentioned above except the digi+.
     
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  8. numbercube

    numbercube Acquaintance

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    I would for for no transformer because it would be one more part that skews the required 75 Ohms of SPDIF. The less shit, the better. A BNC output would be ideal.
    But: I don't think the exact wave impedance is that important. Neutrik's XLR sockets aren't exactly 110 Ohm and yet AES/EBU can keep up with BNC, based on my research.
     
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  9. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    I added a SPDIF coax input with transformer. I also put some 0 ohm resistors to allow us to build without the transformers. Like Digi+ we'll offer with and without transformer versions. Price will be $39 without and $49 with. Although we have much better power supply specs and the better clocking option, we're just $5USD more than them. As I said before, our pricing is based on our cost. And these just don't cost that much!

    The design is going through internal review today and will go to fab tomorrow or Wednesday. Again, many thanks to all who helped refine this idea and special thanks to Vastx for the prompting in the first place!

    Cheers,
    Michael
     
  10. fraggler

    fraggler A Happy & Busy Life

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    Thanks for the efforts, Michael! I need to get to work building my LPS now.
     
  11. Vastx

    Vastx Almost "Made"

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    39/49$ ? It is a killer price! Kudos for the price policy. I imagine audio enthusiasts already owning the digi+ will give it a shot at this price.

    Thank YOU Micheal for the design and the nice interaction with the community here. It is the first time I see something like this happening so fast.

    What did you decide about the clock upgrade pcb layout?
     
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  12. tboooe

    tboooe Facebook Friend

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    I am VERY interested in this. Count me in. I actually just bought a Digi+ Transformer model to use with my Pi3. My plan was to isolate the power supplying 5v to Pi and 5v and 3.3v to the Digi+ separately with my linear power supply. I read somewhere that the Digi+ only needs 3.3v if you use the coaxial output and not the optical which is what I intend to do. I wonder if there is more improvement to the sound if we don't supply the 5v? Anyway, I am in and so looking forward to this.

    If you need help with testing let me know.
     
    Last edited: May 2, 2016
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  13. tboooe

    tboooe Facebook Friend

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    This is the setup I will have once my Digi+ gets delivered so I will be able to compare to this design. I still may try to at least power the Pi3 and Digi+ separately with my linear power supply though to hear if there is a difference.
     
  14. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    I stayed with the small SMT clock selected by GPIO. I really feel the NDK2520SD clocks are such a big upgrade from the PLL, while being better than much more expensive Crystek parts. See this from DIYINHK on the hifiduino web site:

    [​IMG]

    [​IMG]

    While there is room for improvement, I just feel it's about as good as you can get for the money. Back in the days of my 68 Plymouth Roadrunner we had an 80/20 rule: that last 20% of performance cost you 80% of the total!

    Cheers,
    Michael
     
    Last edited: May 2, 2016
  15. Vastx

    Vastx Almost "Made"

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    I can live with NDK2520SD too. I know it's the better C\P option. Still... you know... there's a bit of foolish audiophile in me who loves shiny clocks, big caps and fancy connectors. But deep inside I know you're right :D

    I can't wait to compare this hat to the digi.
     
  16. Merrick

    Merrick A lidless ear

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    Me too!

    [​IMG]
    "Let the great experiment begin!"
     
  17. tboooe

    tboooe Facebook Friend

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    Sorry for jumping in a bit late on this awesome idea, but I was wondering if this board will need 3.3V? From reading the description only 5V is needed? I hope so because that would make things easier.

    Also, I know this board was designed to a price point, but if someone was willing to pay more what could be improved? Maybe a really good coaxial socket from WBT can be used. Maybe an "audiophile" version could be made for sale at a higher price? I am not sure what if anything can be improved but considering the silly amounts of money I have already spent on my audio system for tiny and non-existent improvements, whats a few more bucks?? :)
     
    Last edited: May 2, 2016
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  18. fraggler

    fraggler A Happy & Busy Life

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    I think you meant "audiophool." A WBT connector costs more than the Raspberry Pi.
     
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  19. Vastx

    Vastx Almost "Made"

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    @tboooe
    The board as a nice onboard regulator (lt3042) so no need to go for a dedicated 3,3v.
    We already told Micheal we wanted to spend more... but you know... he's an engineer, he doesn't get us audiphiles like our beloved fancy audio brands do (just joking).

    Nonetheless... 200$ is a crazy amount of money for a pi hat. The implementation already looks pretty good. You could use better clocks but don't expect crazy improvement. Screw WBT connectors. Get a good psu, a nice 75ohm cable and save some money this round.
     
  20. tboooe

    tboooe Facebook Friend

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    Audiophool for sure! Thats me! I dont mind paying a few bucks more to get an improvement, real or perceived! LOL.
     

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