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Chord Mojo DAC-amp ☆★►FAQ in 3rd post!◄★☆

Discussion in 'Portable Source Gear' started by Mython, Oct 14, 2015.
  1. flyte3333
    Hi, do you have the same issue with lower DSD rates?

    You can test free samples from here:

  2. Number9redreD
    Nope. All of my DSD64 & 128 stuff work perfectly
  3. flyte3333
    What’s the make and model of your DAP?
  4. Number9redreD
    FiiO M11
  5. flyte3333
    Last edited: Sep 13, 2019
    Totoxio likes this.
  6. Number9redreD
    flyte3333 likes this.
  7. flyte3333
    Absolutely no problem at all. Always happy to help.
    Last edited: Sep 14, 2019
  8. flyte3333
    Hi @Rob Watts

    Just wondering if you had a chance to see my query:


    I guess the crux of my question is: how is time domain performance not affected by your deliberate change to frequency response (in the case of Mojo's deliberate HF roll-off)?

    For both RBCD content and also hi-res content.

    Are the transients of the original recording (both RBCD and hi-res) fully preserved when using this deliberate high frequency response roll-off with Mojo? And I assume it's similar to the HF filters of Hugo2/Hugo TT2/Dave?

    If my understanding of anything is incorrect, please feel free to correct. I enjoy reading your technical posts and learning.

    Cheers again !
  9. Rob Watts
    Yes I just read your post ten minutes ago. It's been a crazy couple of weeks with work deadlines and travelling. Your post was interesting and pertinent so I will answer now.

    Yes those plots are accurate; indeed all my DACs have analogue bandwidth limiting - so Mojo is set to 45 kHz (-3dB), Hugo 2/TT2 is at 60 kHz - and the plot shown agrees with this.

    And bandwidth limiting is a very good thing, and absolutely nothing to do with transient reconstruction accuracy in terms of timing. A bandwidth limit is linear (that is it creates no form of harmonic or inter-mod distortion), but timing transient errors when the timing of transients are constantly being modulated is non-linear. Bandwidth limiting on it's own I believe to be completely inaudible to humans, as nobody can perceive above 20 kHz; but transient timing errors, where timing is being constantly modulated, most definitely is audible, as these timing errors are directly perceivable by the brain - it interferes with the ability of the brain to perceive sounds.

    So if bandwidth limiting on it's own is inaudible, why do I do it? Well we can't perceive 20 kHz and above, but noise above 40 kHz can have in band audible consequences. So imagine you are using Mojo as a DAC feeding a power amp. Any RF noise (or noise above 40 kHz) will create noise floor modulation, and that distortion is white noise within the audible bandwidth, which in turn makes the sound brighter, harder or aggressive - or less smooth. So it's important that a DAC controls the out of band noise (and by this we have to worry about 40 kHz to 10 GHz. Now Mojo uses a 4e pulse array, Hugo 2/TT2 is a 10e pulse array. And 4e is used for power and cost reasons; but the downside to 4e is that it creates more RF noise than 10e, so this noise has to be more aggressively filtered. Now I could do this by using a 3rd order filter rather than 2nd, but this would add more components in the signal path and so degrade transparency - something I definitely don't want to do. So I controlled it by reducing the bandwidth from 60 kHz to 45 kHz.

    This only applies with Mojo running with amps, with headphones I have no evidence - subjective, measurement or theoretical, that it can degrade things at all (that is the presence of RF noise creating noise floor modulation within the transducer). And I don't believe that bandwidth limiting itself is a problem at all, so long as it is a entirely linear effect (linear applying to any form of harmonic distortion or inter-modulation distortion).

    I hope this explains why a measured bandwidth limit (so long as its perfectly flat at 20 kHz which all my DACs are) certainly isn't a subjective problem, indeed it's an indicator of quite the opposite - and that things are always more complex that they might appear at first sight.
    Last edited: Sep 14, 2019
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    JamieMcC, Matpar, flyte3333 and 3 others like this.
  10. flyte3333
    Thanks so much Rob! You're a legend.
    ZappaMan likes this.
  11. Matpar
    Gosh, wanted to look for some info on my Mojo, gotta read some post here now.. :)
  12. Matpar
    Going to have soon an X20, in the meanwhile I did wonder if It could be fine to Explore options with X10T II as a transport for my Mojo, to be used as a smart home rig.

    I was Just curious to know if coax would have been (as usual, for me at least) Better than USB with Mojo, I have a spare USB C to coax cable from cayin that I hope might work ... Maybe I Will check both (coax 3.5 and USB C).

    I agree with you about having such few Infos on an item like this..
  13. adeseaso
    I prefer Coax.

    I got an Allo Digione again shortly after the Xduoo and haven't really touched the Xduoo since. Turns out portability wasn't all that important to me and I think the Allo sounds better at the same cost.
    Matpar likes this.
  14. samuraivoodoo
    Trying to buy a mojo+poly, are there still problems with this playback wireless?
  15. jarnopp
    I do not have any problems with wireless playback on iOS in any of the 3 wireless modes: Roon, Poly hotspot, or DLNA. SD card via MPD also works fine. You just need to find the right apps that .org for you (e.g., mConnect, Tidal, Glider, etc.).

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