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MDAC First Listen (part 00100011)

Discussion in 'audio' started by highfi, Nov 3, 2014.

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  1. iansr

    iansr pfm Member

    I've read posts by John Swenson on various forums over the years and he certainly seems to know what he's talking about ( but then I don't know enough to discern otherwise) so I'll be interested to read what John has to say about Swenson's observations.
  2. JohnW

    JohnW pfm member


    The MDAC2 will have 2 layers of isolation between the USB port and the analogue sections - not to mention that the critical analogue circuits are on a separated PCB :) Every effort is being made to reduce what I call second order effects (unwanted coupling between the digital domain and "Analogue" sections).
  3. JohnW

    JohnW pfm member


    The MDAC is a better DAC then the CDQ - do we have a salvaged unit for you? I could add AV bypass to your MDAC to tie you over until MDAC2 is ready (as I'm so late on the project).

    Sorry for putting you in this situation - its 1.20am here in Czech and I'm still working on the PCB layout of the Analogue PCB.
  4. ultraviolet

    ultraviolet Member

    Thanks. I'll give it a decent listen next time see how it goes. :cool:
  5. Nick1881

    Nick1881 pfm Member

    Hi John, I don't have a salvaged unit, just my one here. If it's not too much trouble I would gladly ship it to you, this really would be a great help. If it's ok I'll email you. Thanks
  6. Julf

    Julf Facts are our friends

    It is a very confusing thread, as most of the thread is about the possible effects of source processor load, and John Swenson pretty much directly states it is not an issue at all (in his explanation of how the USB interface actually uses DMA to get the data, independent of host CPU).

    What he talks about is noise arising from the simple fact that data arrives in packets, and the digital parts of the DAC interfere with the analog parts due to the bursty nature of processing. Thus cables and interfaces have very little effect, and it seems the implication is that pure bit-oriented protocols (such as SPDIF) are actually better than packet-oriented ones such as ethernet and USB.

    Not sure I entirely agree with John Swenson, but it is an interesting observation.
  7. JohnW

    JohnW pfm member


    Fine - I'll PM you our address :)

    Just ship your unit (WITHOUT AC Adaptor, RC handset etc. to save on shipping weight).
  8. fusion5

    fusion5 on the dark side of hifi...


    Please check your pm.

  9. ultraviolet

    ultraviolet Member

    What's the reasoning behind the digital outputs - two Toslink Optical and two Coaxial. Does high end audio use Coax for the most part, everything I have has Toslink, my Sky TV box, my Sony CD changers and my PC sound card.

    Having to use those Toslink to Coax adaptors that needs to be plugged in to the mains is an awkward solution and probably doesn't aid sound quality.

    Is it possible to have an MDAC's Coax sockets replaced with Toslink?
  10. JohnW

    JohnW pfm member

    "Cheaper" consumer devices tend to use Optical Toslink - Toslink is generally frowned upon by the HiFi industry.

    The Digital output can also be used a Clock output for Clock-locked external CD transport etc. Normally the digital output is used for Digital sub-woofers, processor & recorders etc.

    The MDAC2 has 3 optical inputs.

    Its not possible to replace the MDAC's Coax Sockets with optical receivers as they have a very different PCB footprint and circuit requirements.

    Is there a reason your using the SPDIF output from your sound card instead of the USB port which will give you higher performance?
  11. ultraviolet

    ultraviolet Member

    Thanks, great DAC by the way.

    I am using USB at the moment but the cable is 5 metres, my PC is across the other side of the bedroom. Tends to cut out every now and then and I get the flush the buffer message. I assumed Coax would get me 192 kHz quality - at the moment I am listening to a 192kHz test track and the MDAC display still says 24bit/96.0kHz.

    Downloaded them from here.
  12. misterdog

    misterdog Not the canine kind

  13. JohnW

    JohnW pfm member


    Over SPDIF the MDAC will replay what is sent to it upto 192KHz - so for some reason your PC is down-sampling before sending to the MDAC (which is never a good thing) - good luck trying to find out where and why!

    Are you sure you sound card can support 192KHz?
  14. ultraviolet

    ultraviolet Member

    Good point, I assumed it could. Audigy X-Fi. Best check that!

    24-bit Analog-to-Digital conversion of analog inputs at up to 96 kHz sample rate
    24-bit Digital-to-Analog conversion of digital sources at up to 96 kHz to analog 7.1 speaker output
    24-bit Digital-to-Analog conversion of stereo digital sources at up to 192 kHz to stereo output
    16-bit to 24-bit recording sampling rates: 8, 11.025, 16, 22.05, 32, 44.1, 48 and 96 kHz
    ASIO 2.0 support at 16-bit/44.1kHz, 16-bit/48kHz, 24-bit/44.1kHz, 24-bit/48kHz and 24-bit/96kHz
    Supports Sony/Philips Digital Interface (S/PDIF) format of up to 24-bit/96 kHz quality
    S/PDIF output at selectable sampling rate of 44.1, 48 or 96 kHz
    S/PDIF output not available during playback of protected digital audio

    Think I will unplug one of my CD Changers and use my Toslink cable to the MDAC from my PC, see what happens.
  15. jirij

    jirij Virtual Member

  16. JohnW

    JohnW pfm member

    Seems your sound card can only support 96KHz via SPDIF

    "Supports Sony/Philips Digital Interface (S/PDIF) format of up to 24-bit/96 kHz quality
    S/PDIF output at selectable sampling rate of 44.1, 48 or 96 kHz"
  17. ultraviolet

    ultraviolet Member

    Thanks for the help, might invest in a new sound card or a network streamer, put all my CD's on that.

    I installed the Realtek HD Audio driver and connected it to my MDAC from the motherboard Toslink output and it did have the 192kHz option in it's control panel but no sound at all came through, switched to CD quality and it played other music okay. All very confusing.
  18. JohnW

    JohnW pfm member

    MDAC's Optical inputs do not officially support 192KHz - although in most cases if the source is low jitter it will work OK - we use Juli@ Sound card which is stable and works well
  19. SirBenn21

    SirBenn21 pfm Member

    Just wondering when the expected ETA for the MDAC-2 is.

  20. JohnW

    JohnW pfm member

    I'll be issuing the Analogue PCB files by the end of the month - the Analogue PCB is the heart of the design and is by far the most complex part of the project.

    I'll need to debug the Analogue PCB (I've already debugged various sections of the board with the two earlier PCB spins which revealed only a few minor areas that required design modification, so hopefully there will be no major show stoppers) and then I'll issue the production files.

    One I've completed the Analogue board, I'll start work on the digital PCB this will take about 2 months to complete - so production will start around mid to end of Q1.

    Last week I've been making arrangements to meet local SMD vendors to discuss the PCB production - so the light is finally visible at the end of the tunnel.

    I must say that when I scan over the Analogue PCB I'm very proud of the design - it should be stunning, in fact its almost crazy when you look into details of each circuit block. I'm really fascinated how its going to sound as there is no existing design with so much circuit optimisation and attention to detail.

    I've developed new circuits for the Power supply's, Analogue stages and clock circuit so its like nothing I've designed or seen before.
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