Modi Multibit i2s input mod

Discussion in 'Digital: DACs, USB converters, decrapifiers' started by Scott Kramer, Nov 8, 2016.

  1. Scott Kramer

    Scott Kramer Friend

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    #1 -- Useless but interesting side effects from the i2s Moby [Documentation]

    A free async USB to i2s converter:

    IMG_0872.JPG

    No wall wart needed... the USB CM6631A is powered on by pc 5V?!?

    Extended that 5V to an external pin (the separate red wire) to power the external cheap ass test sabre DAC (couldn't get myself to spend more than $9 on a 9023 sabre)

    Also a 2nd MCLK out (red wire) not going thru schiits large resistor (this is too low for the ext DACs I tried).

    RED->5V

    RED->MCLK (MASTER CLOCK) 22/24 MHz
    BLUE->BCK (BITCLOCK) 2.82/5.64/11.2 MHz
    YELLOW->LRCLK (LEFT-RIGHT CLOCK) 44.1/48/... KHz etc.
    WHITE->DATA (LEFT-RIGHT CLOCK) * 32
    BLACK->GROUND

    And this simultaneously runs... I could power the Moby and use i2s/coax/opt.

    Nice independent circuit they implemented here.
     
    Last edited: Apr 6, 2017
  2. Scott Kramer

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    @auri -- Any plans on this?
     
  3. auri

    auri Facebook Friend

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    Just gotta tear my main Bifrost Multibit apart and pilfer its USB board. I've got a bit of a lull in cabinet building waiting for my woofers to show up so I'll get to it soon. :)
     
  4. auri

    auri Facebook Friend

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    Bifrost i2s input. Waiting for a new RPi board to come to use with my 502DAC to test it. I have no idea if this will work, please don't blow anything up if you try it out. :)

    Since images won't last forever, the Bifrost i2s input from the USB board is on the shorter header row of 8. Counting down from the rear of the board, pins 1, 3, 5, and 7 are all Ground. i2s is located on the following pins:

    Pin 2 - Master clock
    Pin 4 - Bit clock
    Pin 6 - Word clock
    Pin 8 - Data

    As for how to fool the Bif into thinking a USB card is installed (and letting you select it), Pin 6 on the longer header is used for some mysterious, undoubtedly nefarious purpose as it connects the CM USB chip to Pin 11 of the Cirrus Logic 8416-CSZ SPDIF receiver. Pin 11 is RXSEL0, which will determine where the Cirrus chip gets it's positive AES3/SPDIF input from. I have no idea how this works and how it might be related to the 2-way HC157AG i2s router that directly feeds the DAC board (and that the USB pins I mentioned lead to).

    Next I will try to trace Pin 6 to a specific pin on the USB chip to see if I can find out what signal it might be sending and when.

    [​IMG]
     
  5. Scott Kramer

    Scott Kramer Friend

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    @auri

    Awesome! Look around for a logic pin(s) (3.3V, maybe 5V) going high or low based on USB being selected or not. Then you can tie that to 3.3V (with a 10K limiting resistor to be safe) or ground. Also see how it behaves with the board in or out.

    That pin11 may be disabling the cirrus chip when usb active... the moby is a bit different, there are 2 i2s paths since they are less than an inch long... the bifrost, it looks like 1 long i2s path w/a buffer chip (guessing).

    Do you have any sort of i2s source to test with yet?

    Also is there a PIC microcontroller or something similar? The moby uses the DSP as a simple microcontroller (input selection etc) to save space. This might complicate it a bit.


    Throwing some ideas out there for you.
     
    Last edited: Mar 29, 2017
  6. auri

    auri Facebook Friend

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    I'll bet it is disabling the Cirrus chip, that makes sense. Sort of a backup plan to the i2s router (which has a mode to enable both inputs).

    No i2s source at the moment, my current RPi board decided to stop detecting i2s soundcards - thought it was just the Digi+ Pro that I sent back, but doesn't work with my new 502DAC no matter what I try software wise. I've got a new one on the way, but Amazon Pleb might take a little while.

    Also yes on the microcontroller, it's a PIC24FV16KA302.
     
  7. Scott Kramer

    Scott Kramer Friend

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    Take your time, don't hack anything up! There's probably a very elegant way to do it. I really need to get a gummy, to work on it with you!

    I'll look into the PIC and i2s router chip... what chip is near the i2s test points?
     
  8. auri

    auri Facebook Friend

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    HC157AG. Here's the data sheet.. USB i2s enters via the B inputs. Didn't trace the leads but I'm assuming the A inputs go to the Cirrus receiver. Then the Y outputs connect directly to the DAC board headers/test points.

    I won't be hacking on anything, even if I am currently sitting on four bare Bifrost boards plus my Bifrost Multibit. :)

    Also, the lead running from the USB chip to the Cirrus receiver has +5v normally with the USB board out and in, but with the board in AND USB input selected it's +1.5-2v.
     
  9. auri

    auri Facebook Friend

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    I titled this piece A Rainbow Over Schiit.

    Doesn't work. Doesn't work at all. Just a bunch of snap crackle and pop. Didn't break anything at least.

    @Scott Kramer or @Michael Kelly did I read a post by one of you that Schiit i2s was somehow different (slower?). 128M vs 256M?

    Also still need a way to fool the Rost of Bif into thinking there's a USB card in there.

    [​IMG]
     
  10. Scott Kramer

    Scott Kramer Friend

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    Hmmm, not a multibit. The AK4490/4399 will probably take any i2s Fs (x128/x256) (MCLK multiple).

    You need to plug in the USB cable to trick it for now... to let the bifrost select USB. You're probably overlapping with the cirrus i2s.

    Edit: Do I only see 4 i2s lines? Do you have the GND hooked up? Every other pin on the i2s header are probably grounds.
     
    Last edited: Apr 6, 2017
  11. auri

    auri Facebook Friend

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    HOLY SHIT IT f'ing WORKS

    All I had to do was plug in a USB cable.

    :eek::eek::eek::eek::eek::eek::eek:

    Edit: Connected a GND. Everything still works. :D
     
    Last edited: Apr 6, 2017
  12. Scott Kramer

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    Cool! Yes connect a GND! Otherwise it's going around the bend (thru the power ground.)
     
  13. Scott Kramer

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    Beautiful! Now for some short as possible i2s connections, or just listen and have fun to start. Can always clean up the logic later...

    Didn't you just get the 502? Play around with the BNC yet?


    Congrats on the special f'n snowflake DS Bifrost! (thats what I call the Moby)
     
    Last edited: Apr 6, 2017
  14. auri

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    The BNC works great, this is just more betterer. :D I also wanted to save the SPDIF input for a PC.

    The reason I doped this out was for my Bifrost Multibit. What would have to change (for the clock multiple) for this to work?
     
    Last edited: Apr 6, 2017
  15. Scott Kramer

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    Whoa... don't be bugging @schiit?!?

    All you need to do is look for a logic level going high/low when plugging in/out the USB cable.
     
    Last edited: Apr 8, 2017
  16. auri

    auri Facebook Friend

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    Yeah, you're right.

    Seems like I need two, USB card in so you can choose USB input, and then USB cable in so it actually works... Couldn't even find the first one last time, but I'll try more this weekend. Where should I look? Pins of the microprocessor?
     
  17. auri

    auri Facebook Friend

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    Thanks. I've got a black Moby on the way. No way am I hacking on that thing. LOL
     
  18. Scott Kramer

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    Might be good to listen a bit, get used to the sound... then go to the i2s. But yeah it's kinda kick ass at least w/the Moby.

    Ok, I thought you had a Bifrost Multibit, was surprised to see the DS board.

    The moby multibit expects Fs x128 at 44.1/48 -- The Digi+ PRO does this, and the higher bitrates all correctly. The 502 is Fs x256 at 44.1/48 -- you have to upsample that to 24/96. No way to change the Fs on the 502.

    I have a nice chart, might post it next week sometime.

    Yikes.

    I'd start with the long header, one of those is probably going high/low. Measure the state of each with USB in, once with USB out.

    Yep, micro solder SMD parts involved. Tricky, but not too bad with the right tools. Not knowing if it was even possible, and tracing the circuit was the hardest part.
     
    Last edited: Apr 26, 2017
  19. auri

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    Sounds pretty good. :)

    [​IMG]
     
  20. Jeffjazzer

    Jeffjazzer New

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    Hey, Scott Kramer I did my homework and figured out all the I2S connections going from the Modi Multibit to 502 Dac. I cannot see where the jumper wire on back connects to, so USB stays on.
    I see the 3.3 volt pin, but can't tell where that connects to. Looks like to the left side of R42 just below DSP chip? There are 3 other super tiny pins above R42 and you may have use one of these (don't think I could solder something that tiny)? I prefer not to have to hook up the USB cable to get 5 volts. Need to know where to " jump". (Without David Lee Roth's help :) Thanks
     

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