Raspberry Pi I2S to SPDIF Hat

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

  1. tboooe

    tboooe Facebook Friend

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    I need to look at the specs of the LT3042. I have some LT1963 based regulators that have very good performance. Also, in the past I have investigated Belleson regulators too which have very very good specs.

    I already have a very good linear psu and cable so I am just looking for ways to throw away more money!

    BTW, any idea how this board would work with RuneAudio, Volumio, Moode, etc? Will a special image for each player be required?

    [​IMG]
     
  2. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    The 3.3V is generated by an on-board low noise LDO. It has a very high (PSRR (Power Supply Rejection Ratio) over 80db through the entire audio range. That means any noise on the 5V rail is reduced by a factor of 80db+. Coupled with the high frequency filtering we add on the 3.3V line, Power Supply noise should be virtually non-existent.

    Adding you own low noise 5V supply will improve the noise and jitter as will using high quality coax cables. Whether they are audible improvements..... we shall see!

    As Vastx said earlier, the board will have to tested to see if it is better than Digi+. Vastx, Fraggle and PhilMorgan have agreed to be my test dummies. Their feedback will be critical to point me in the right direction as an engineer.

    Cheers,
    Michael
     
  3. tboooe

    tboooe Facebook Friend

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    Ok, looking forward to the results. Not sure if anyone will be testing on a Pi3 but I just got one if you need additional testing help.
     
  4. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    This is pretty cool and sounds like a good deal. Let me know if you decide to make a cost no object version with 75ohm BNC outputs and AES, maybe even a regular RCA output too for those that need it. ;)
     
  5. tboooe

    tboooe Facebook Friend

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    YES! Thats what I'm talking about! Audiophile (or audiophool) version please! 110ohm AES and 75ohm BNC would be pretty cool.
     
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  6. Wfojas

    Wfojas Friend

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    Hey, I can test for Picoreplayer and Roon Bridge too, if you need a tester. Audiophool version up here, also, but only if i can blind test it.
     
  7. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    I think you'll be happy with the LT3042! PSRR of the LT3042 is more than 80db 10Hz to 60Khz while the LT1963 is 55db at 10Khz drops to 45db at 20Khz. Noise from the LT3042 is 0.8 micro-volts RMS from 10Hz to 100Khz while the LT1963 is 40 micro-volts RMS from 10Hz to 100Khz, or 50 times higher!

    By default the 27Mhz crystal will be enabled and any player that supports Digi+ should just work. To access the low noise clocks we make a few, small modifications to the sound driver in Linux and then we build the player SW on top of that modified Linux. We will submit our changes to the Linux codebase and then, when the player supplier builds their latest version our code will be in there. But that could take 3-6 months depending upon how often the player software is updated by the vendor. Until then you will need to either get the modified player from us, or the modified Linux driver and build the player yourself. That's why we're only looking at supporting Volumio, RUNE Audio and OSMC (OpenElec). But, as I said, once these changes are in the linux base, any player that is updated will get the changes.

    Cheers,
    Michael
     
  8. uncola

    uncola Friend

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    dumb question but can HATs be used with heatsinks attached to the raspberry pi? the type that come with the canakit bundles?

    [​IMG]
     
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  9. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    We use 18mm standoffs on our hats to insure clearance. We support both the Up-Board and the Odroid with some hats, and they have even bigger heatsinks.

    Michael
     
  10. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    In case it was not clear, the Kickstarter campaign for the 503HTA Hybrid Tube Amp has begun. We waited a day to let the folks who signed up on our web site get first crack. Now everyone on this thread can get one. Later today we will go global with various google+ groups, the Raspberry Pi community and several web sites, blogs, etc. The Kickstarter page is:

    https://www.kickstarter.com/projects/1815752970/hybrid-tube-amp-for-the-raspberry-pi
     
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  11. frenchbat

    frenchbat BritishBat's arch enemy - Friend

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    If this thing gets AES then I'm game.
     
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  12. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    The Wolfson WM8804, which is what is used on the Digi+ and we are using, does not support balanced outputs. The Cirrus (who happen own Wolfson now) CS8406 does. I can easily crate another hat that uses the Cirrus device along with the other enhancements we did. BTW, AES uses the XLR, which is a very large connector. What about using the mini-XLR? As for BNC, would that be 2 outputs to provide +/- or one for single ended?

    Cheers,
    Michael
     
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  13. frenchbat

    frenchbat BritishBat's arch enemy - Friend

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    I guess that'd mean custom cable, min-xlr to xlr, but you could also provide it for a fee. How would the CS8406 fare compared to the wolfson ?
     
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  14. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    According to the data sheet the WM8804 has 50ps RMS jitter while the CS8406 has 200ps RMS. Not as good as I would like. However, the TI DIT4192 does not use a PLL so jitter/noise is based on the input clock, which will be very high quality. Looks like a winner. The only downside is there is no existing hat with this chip, so we will have to modify the players as discussed before. Not Digi+ clone mode! :(

    And I think I understand the use of the BNC, it replaces the RCA, correct?

    Cheers,
    Michael
     
  15. tboooe

    tboooe Facebook Friend

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    Thank you for the reply. Will you be making a modified player from the beta releases as well? Right now, only the Beta release of Rune supports the Pi3.

    Also, I know you said you already had testers but in case you havent considered it, it would be good to test with users and systems with a range of capabilities, from casual listeners to SOTA audiophile systems. Just my 2 cents (and shameless plug for my 2-ch only system which I consider pretty good).
     
    Last edited: May 3, 2016
  16. tboooe

    tboooe Facebook Friend

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    For absolute best sound possible I am cool with no Digi+ clone model but of course thats easy for me to say as its more work for you not me!

    And yes, BNC would replace the RCA connection. I believe the reason for the preference is because BNC provides a true 75ohm connection whereas RCA does not. That being said, lots of older DACs do not offer BNC input so then an RCA to BNC adapter would have to be used. As much as I like BNC I think RCA would appeal to a wider audience. Check out the following link for more info:

    http://www.bluejeanscable.com/articles/75ohmrca.htm
     
    Last edited: May 3, 2016
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  17. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    You gotta love Google! Some quick searching turned up that I can drive the WM8804 output to a balanced XLR using a high speed RS422 driver. In fact, when you look at AKM's drivers they specifically state it is an RS422 driver. Did some more searching to make sure and found several sources backing it up, including the AES3 Wiki.

    So now we'll have the same HW as 503SPD1 but with balanced XLR out. And because we are using a discrete buffer I can drive a BNC at the same time. Both with transformer coupling optional.

    New board will be called 503SPD2. Yeah I know, dullsville!

    Cheers,
    Michael
     
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  18. tboooe

    tboooe Facebook Friend

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    Alright enough talk. Take my money now.
     
  19. Vastx

    Vastx Almost "Made"

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    Nice, same receiver.
    How would the balancing addition change the price?

    Could it be possible to have all of this in a single board (toslink\coax\bnc\aes) or you want to make separate board?
     
  20. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    If you make a cost-no-object (best parts you can source for lowest noise, jitter, etc.) SPDIF hat with at least BNC output, guaranteed to 75ohm like I suggested earlier, and keep it under, I dunno...$500? $1K? I'll sign up and give it a shot. Well, once I have the money. I could swing a couple hundred now, more later. :) What I wouldn't have is money for LPSUs at that time, ha.

    We need more solutions that are geared just for audio and bypass USB. I think that's the way to go, and I'm really pissed at all the digital audio transports on the market that cost well over $1K. If we could get a heavy hitting hat to compete at a low cost, that would be awesome. And someone can just use the Mutec 3+ USB if they want to go totally balls deep with another decrapifier/reclocker product, since many seem attached to having as many components in their source chain as possible. ;)
     

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