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

Discussion in 'Portable Source Gear' started by Mython, Oct 14, 2015.
  1. GrussGott
    (1.) I use it with my HD600s and I think it sounds great - to my ear the mojo sound is "relaxed" and rolls off the highs and sub-bass compared to other DAC/amps, but that's subjective. I definitely wouldn't call it too warm.

    (2.) Yes, can't say iPhone as i've only tried that once, but with android phones on LTE, definitely. I've tried it with 4 and they all cause EMI issues, although for me it's not strong or loud, but you can hear it in between songs

    (3.) No idea
     
  2. RiseFall123
    I know it’s a little off topic but here somebody tested the oppo ha-2 se and could advice me? That oppo seem less fuzzy for everything. Remember my only cans are th HD650.

    And i am afraid about those noises and all that cables involved to mojo.
     
  3. Rob Watts
    Yes I was sent a DAC which I measured noise floor modulation, but I decided not to publish, as I prefer to just talk about my own stuff; after all I could get accused of cherry picking evidence, or other such stuff. And my job is to talk about my work, not other peoples. But since I am being accused from another poster of "being a truck of hot air" now, here was the data:

    competitor 2.5v with -999dB.jpg

    So you can see lot's of issues, which are normal for a chip based DAC. The first one is noise floor modulation, with the noise floor moving from -165dB to -155 dB at 2 kHz; note Mojo is at a constant -175dB, that's ten times lower. You can see skirting issues around the fundamental, this is another type of noise floor modulation, with the skirt extending to -140 dB; in my listening tests these skirts have been shown to be highly audible. Oddly, they sound identical to noise floor modulation; removing the skirts and it gets smoother and warmer. The most likely source of this is low frequency jitter on the master clock. You can also see quite high levels of harmonic distortion peaking at -100dB (2nd) and -106 dB (third) , with Mojo being at -136 and -130 - that's about thirty times lower. More worryingly, are the anharmonic clusters around each harmonic at around -150dB; these are the noise shaper activity being demodulated by the DAC; it's most likely a consequence of signal correlated switching activity, or signal correlated jitter on the master clock. The ear/brain is good at dealing with harmonic distortion, as the ear is non-linear; but it's not capable of tolerating anharmonic distortion, as it does not occur in the natural world.

    This device is actually quite good compared to some high-end audio DAC's, where low frequency distortion can reach more than 1%, with even larger levels of noise floor modulation.
     
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    Light - Man, miketlse and maxh22 like this.
  4. GrussGott
    Hi Rob, would you support blind testing at CanJam or other venues where a group of, say 100, listeners would blind test, say, three portable DAC/amps: Mojo, Ifi iDSD BL, Fiio Q5? If the Mojo is superior in sound, what better way to prove that than a blind test?

    Seems like most consumers just want to know: does the Mojo sound better to me than its competitors?

    And if experiential testing is opposed (e.g., everyone hears things differently, so wouldn't prove anything) then why go to all the trouble of posting all of this technical data?
     
  5. Rob Watts
    The problem with blind testing is twofold - firstly the minute you add stress into listening, then your sensitivity falls. If the actual DUT is not identified (A B or C) and truly random, then sensitivity collapses even more.

    The second issue is qualitative. I remember a research paper "proving" that a Stradivarius violin was as good as a modern inexpensive violin. They blind tested these violins, and half the audience preferred one, the other half preferred the other. So there you have it - they sound the same. Of course, that was nonsense - the Strad is warm sounding, the modern violin is quite bright. If they had re-framed the question to which is the warmer sound, then you would have got the right answer - the majority of the audience would easily be able to spot the warmer violin. I once heard on the radio in my car, somebody doing a blind test with a Strad against a modern violin, and it was easy to hear which was the Strad - even in my car on the motorway - the Strad sounded a lot warmer. But some people like bite and a bright sound; and the same is true with audio. The issue with DAC's sounding different is actually not that they sound very different, but that some people actually "like" or rather think they like, the sound of distortion.

    I actually employ blind listening tests when the results of a test is so challenging or significant technically, and so I need to confirm my own listening tests. So listeners are asked to hear this, hear that, without knowing what they are listening too, and characterise and describe the difference. If under blind conditions it is audible, then it means one has to accept the evidence as fact, even if intellectually it may be challenging (the ear/brain can't be that sensitive)...

    But I don't see your problem - try one at home, and if you don't like it send it back. If you can't hear the difference, then don't waste your own money.

    And yes sometimes I do wonder why I go to all this trouble posting technical stuff...
     
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    https://www.facebook.com/chordelectronics https://twitter.com/chordaudio http://www.chordelectronics.co.uk/
  6. GrussGott
    Thanks so much for that thoughtful answer, it definitely helps me at least.

    As for "my problem", it's not really for me anymore as I bought a Mojo a few months ago and I think it sounds great -- combined with the design, the size, etc it's definitely a keeper for me (I still think it's over-priced, but hey, subjective!). Overall I'm a satisfied Chord customer.

    For new people coming to this 2,000+ page thread, it could be helpful to skip all of the technical / religious stuff and hear, "in blind testing the mojo is most often selected as the best portable DAC/amp".

    Back to me, I have no sound complaints, and would rather see any effort put into the physical product (EMI, battery, ports, maybe power, maybe bluetooth)
     
  7. theaudiologist
    if the mojo isn't a chip based DAC, then what is it?
     
  8. Deftone
    FPGA
     
  9. theaudiologist
    what's that? and what's the difference between a chip based dac?
     
    Last edited: Nov 22, 2017
  10. GrussGott
    Rather than use off-the-shelf DAC chips like the 4490, Rob wrote custom code (software) that is implemented via a field programmable gate array (FPGA) chip. In short, it's a completely different architecture than anything out there. Whether that means it sounds better is the subjective part ... but it's the premium you're paying for (as well as the design).
     
    Last edited: Nov 22, 2017
  11. Rob Watts
    A DAC has two parts - the digital, and the analogue. Conventional DAC chips use a mixed signal process, so it combines digital and analogue, but typically would be in a 180 nm process. So the DAC designer has to keep the digital parts very simple, as there is not much area and so few gates to do anything complex. Moreover, the digital part is noisy, and upsets the analogue part through the substrate. Also, analogue on silicon is a big problem - resistors and capacitors are non-linear, so one has to go to very complex lengths to reduce this problem.

    But an FPGA based DAC is actually not a DAC; what happens is the digital part is on an FPGA (which is a field programmable gate array) and the analogue part is via discrete analogue components. The beauty of this approach is that you can have an extremely complex digital part, as the FPGA is made with 28 nm silicon, so you can pack many more gates in an economic device; Mojo has 500 times more processing power than usual chips because of using an FPGA. Also, because the analogue part is discrete, there are no issues with noise coupling, and resistors and caps are all linear. When I have desiged the digital parts for a chip, it is fundamentally the same process as designing for a FPGA; indeed, I always prototyped my silicon chip designs with FPGA's.

    But there are downsides to an FPGA DAC; the designer must know what he is doing; and unit costs are very much higher - but that doesn't matter too much for high end audio, where performance is the most important factor.
     
    Chord Electronics Stay updated on Chord Electronics at their sponsor page on Head-Fi.
     
    https://www.facebook.com/chordelectronics https://twitter.com/chordaudio http://www.chordelectronics.co.uk/
  12. turkayguner
    Hello guys, my older USB2 CCK cable is now broken and I need to purchase a new one. Which one should I go for; the same USB2 or the newer USB3 CCK cable? Is there any benefit with the new cable? I am currently using iPhone 5s and iPad Air mini 4. I had some connection issues like the idevices cannot see Mojo sometimes lately but I guess it was because of the faulty cable.
     
  13. jarnopp
    Poly.
     
  14. miketlse
    There are several suggestions for Apple cables in the faq in post #3. Buying some brands of cheap non-apple cables can turn into a false economy, but others are better. I expect that you will get plenty of suggestions to buy the chord cable module, or the Poly - but it is your choice as to how much you want to spend.
     
  15. turkayguner
    Eh.. Poly is cool but I cannot afford it right now.
     

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