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  1. #1
    Senior Member
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    Triode plugin with M-DAC

    Just wanted to gauge from my fellow Touch and M-dac users the best combination.

    1. With plugin and using usb cable
    2. With plugin (set to digital out) and coaxial cable
    3. No plugin and coaxial cable


    Please share your findings



    PS I'm using Belden based Coaxial and cheap usb cable.
    Squeezebox touch
    Squeezeplug running on Dockstar
    Audiolab MDAC
    Arcam A85 amp
    Chord rumour speaker cable
    Dali Mentor Menuets on Custom Design stands

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  2. #2
    Junior Member
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    Dec 2011
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    I have my Touch connected to the M-Dac via coax and can confirm that the plugin works fine with 24 / 192k FLAC's.

    The M-DAC is limited to 96k on the USB input - so personally can't see any advantage in trying the USB connection as access to my (very few at the moment (1 album)) 192K recordings is what I was after.

  3. #3
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    Suggestions

    I'm still waiting for my replacement M-DAC (Original unit had a defective relay and was returned in December!), so can't really write from experience.

    The USB connection offers one key advantage thanks to the asynchronous communications it enables (this should greately reduce jitter). It is limited to 96 kHz but should definitely be worth investigating.

    One other consideration is electrical isolation (mainly form power supplies pollution). You may want to try using a USB isolator (ú20-30 from Olimex or Danish online shop) -Cable quality should not matter, provided the cable is good enough for bog standard USB applications-, or a Toslink/Optical connection with SPDIF (up to 192 kHz sampling rate if so inclined).

    From what I gather from communications with John Westlake, the MDAC designer, its likely that the best results will be achieved via the USB interface and an isolator.

    PS: John plans on designing a 192kHz USB interface for the MDAC, which may be even better, but that's still just a concept.

  4. #4
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    USB Isolator

    Does the USB isolator though just perform a familiar job to a mains filter? If you've got clean mains you don't really need one?

    I'm still to do extensive listening via USB compared to coaxial?

    Anyone else got the same setup?
    Squeezebox touch
    Squeezeplug running on Dockstar
    Audiolab MDAC
    Arcam A85 amp
    Chord rumour speaker cable
    Dali Mentor Menuets on Custom Design stands

    Room 2
    Boom

    Bedroom
    RADIO

  5. #5
    Senior Member Mnyb's Avatar
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    main filter does not isolate the interface Touch to DAC not the same thing, nb I have no idea if USB needs isolation or not , if these products are used for non audio application to then they might have a real purpose (not just fleecing audiophiles ).
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  6. #6
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    Galvanic USB isolators are not the same as mains filters.

    As far as I understand it, galvanic isolators remove the electrical connection (grounds) which exists otherwise, and prevent the introduction of noise into the DAC and its digital and analog circuitry (some of which can be quite sensitive to such pollution). I think that PSU noise is more a factor here than Mains noise. Loboking at the circuit design, the isolators seem similar to the baluns that are used to eliminate ground loops, etc.

    One could achieve the same results with a USB->optical->USB connection, but this costs more than the ú20-30 of an isolator.

    Isolators should not alter the signal and don't have any negative effect (besides cost and throughput limits which are above what is needed for USB 1.0 Audio)... as can easly be checked with the MDAC and its bit perfect test.

    They do provide some added protection to the DAC (and are commonly used with USB experimentation boards and other testing equipment, for this reason).
    Last edited by eiffel; 2012-04-19 at 06:25. Reason: added 'Galvanic' term and more 'technical' detail

  7. #7
    Senior Member
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    I must add that using the Mdac via usb is sounding sweet.Can I be bothered switching back to coaxial? I've never purchased a 192k track.
    Squeezebox touch
    Squeezeplug running on Dockstar
    Audiolab MDAC
    Arcam A85 amp
    Chord rumour speaker cable
    Dali Mentor Menuets on Custom Design stands

    Room 2
    Boom

    Bedroom
    RADIO

  8. #8
    I found optical to a DAC (Cambridge Audio DACMagic) from my Touch (and then into an Arcam A85/Dynaudio Excite X12) to be better than coax. For a ú4 spend it was well worth the experiment!

  9. #9
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    The USB isolators block a potential path for a ground loop through the ground of the USB connector of the "computer" (Touch in this case). Whether this is necessary will of course depend on the computer and DAC and how the power supplies are hooked up. There has been so little use of USB DACs with the Touch that all the reports I know of are using the isolators with regular computers, so may or may not have relevance for the Touch.

    The isolators themselves that I am aware of put the isolator in front of the USB receiver in the DAC, they all use the same chip. These chips DO add a significant amount of jitter to the USB signals themselves, whether this jitter winds up as jitter on the clock feeding the DAC chips (the only place where jitter really matters) is going to be VERY implementation dependant. In some DACs it won't get through to the clock, in others it will. So in some situations it comes down to a tradeoff between higher jitter and lower ground loop noise, or it may not do anything at all. Or it may make things worse!

    My personal favorite approach is to have a USB reciver running off the VBUS with the logic level outputs going through isolators (I prefer GMRs) to the rest of the DAC. This way everything having to do with the USB stays on the computer domain.

    John S.

  10. #10
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    Quote Originally Posted by JohnSwenson View Post
    These chips DO add a significant amount of jitter to the USB signals themselves, whether this jitter winds up as jitter on the clock feeding the DAC chips (the only place where jitter really matters) is going to be VERY implementation dependant. In some DACs it won't get through to the clock, in others it will.
    How does jitter get through an asynchronous interface? Isn't that a bit like talking about jitter on an Ethernet connection?

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