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

Discussion in 'Portable Source Gear' started by Mython, Oct 14, 2015.
  1. Traveller
    @Rob, thanks again - lucky for me that you don't know the emoji for "facepalm"...  [​IMG] (and just to be sure I didn't "email-quote" you this time around...)
    Note to self: Ask yourself at least twice if your question really makes sense before wasting an expert's time with the bloody thing... [​IMG] 
  2. GreenBow
    Thank you for this. Thank you too to Rob Watts for input.
    After my last post I was thinking left wondering whether I was right, or wrong. Since it put the tune in my head, here's the link. https://www.youtube.com/watch?v=Vq7JSic1DtM
    I was wondering about my maths, or if I had impedance upside-down. Since Rob says 8ohm is the peak power draw. Then I guess more load and voltage required is not more power than low impedance current draw.
    I am pretty convinced that the Mojo can not be tailored for my 32ohm requirement with a cooler battery. The battery I had in mind was the Pure on that powers my PocketDAB 1500. I get about eighteen hours play out of it on digital reception. Digital reception uses more power than analogue radio, and analogue radio lasts on the battery for much longer. It takes about four hours to fully charge. It is 3.7V (charged by 5V charger), and 1800mAh. It never gets warm that I noticed.
    Pocket DAB1500 Battery Pack - LP37
    Anyway thank you everyone for clearing the air. Everyone. You are stars*.
    Also I had a bit of a result last night when checking out my other DAC with reference to Mojo clicks. I played Katie Melua (album) - Call off the Search, on both my Meridian Explorer and Mojo.
    I didn't notice particularly any more noise on the Mojo than the Explorer. It was either a case of the album only made one slightly audible click, or something else. What else I don't know. I have been wondering if the issue is caused by the Mojo just better at picking out detail.
    There were other noises but they were of the type that the sound was breaking up a little. Probably due to poor CD-rip or my headphones not good enough quality. ...On close listening to the Meridian Explorer I do hear this 'noise'. However it's kind of smoothed over by the ME being a thicker sound.
    I can't draw any conclusions though. Basically because I recall that album was one that caused most clicks for me. Yet last night it was sort of behaving in normal parameters. Whereas months ago I was a little alarmed. Also the clicks appear random.
    Whatever though I do get clicks in my other PC audio. However I am coming around to thinking maybe that's just normal noise.
    What I did clearly bring from this listening last night was quite profound for me though. After listening back to the ME, then the Mojo, I realised how much more I loved the Mojo. Whereas when I first got the Mojo, quick A-B testing was not so revealing. Even though the Mojo had more clarity. Now however after having used the Mojo for months, the Meridian Explorer was OK. Then when I put the Mojo back on, it was clear and obvious where the beauty of the sound lay. 
  3. Arpiben
    @Rob Watts
    You have been pointing out the importance of transient timing accuracy.
    Your WTA closed form algorithm filter with  xxxxx taps is the one tackling the above issues. 
    Kindly you have been showing excellent THD measurements as well as taking time to explain, among others, the advantages of your filter vs standard half band FIR/IIR in a comprehensive way.
    Please what is your point of view regarding phase variation`s accuracy?
    If my understanding is correct, human hear is much more sensitive with phase variations/distorsions rather than its own real value 
    In microwave radio transmission, Group Delay has to be kept steady all over the transmitted bandwidth....
    In audio transmission by analogy we also have to deal with waves propagation issues (air,cable,waveguides) & analog filters....
    Nevertheless my question is only addressing the [ digital filter (WTA) + Amp ] phase aspect of Mojo.
    Theoretically, Mojo`s group delay measurement should provide as much information as THD.
    For sake of clarity I omitted talking about ADC group delay,transfer function,..
  4. x RELIC x Contributor

    This reason, more than any other, is why I feel the Mojo is such an exceptional device.

    The audio doesn't jump out at you, scream attention to itself, it just plays natural sounding music with a high degree of fidelity. I agree 100% that going back to other gear after spending time with the Mojo is really the only way to truly know its capabilities.

    rwelles and GreenBow like this.
  5. RPB65
    Jean-Michel Jarre via Qobuz on iPhone 6S+, Mojo is just incredible! Never mind the whole album, just put on Equinoxe, part 5.
    I had loads of his albums on cassette! pmsl, ahhh, the days of my vertical record player and dual cassette decks! :wink:
  6. headwhacker
    OTG Support for Android devices usually is only supported/enabled on every brand's top model or flagship. I bought a couple of cheap phones from LG and Samsung but none of them worked via OTG. Finally, I bought an even cheaper, refurbished Samsung S4(used to be their flagship several years ago) and it just works fine via OTG.
  7. jmills8
    onkyo player should work on most phones. Chinese phones will connect the mojo onto various music player apps.
  8. normanl
    Does anyone know where to get stereo 3.5mm M/M cable with ferrite core filters? I'd like to use it to connect Mojo to my preamp and active monitors. I goole-searched it with no result.
  9. Rob Watts
    Well we built more Mojo prototypes than with Dave...
    I don't know, its a Chord development. I think that a case is coming.
    I am talking about the specialist battery charger device - this chargers the Li Po battery and provides levels of protection only for use with Li batteries. There are complex PSU circuits preceding this device.
    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/
  10. Rob Watts
    Designing for high performance audio - when you are interested in making something as truly transparent as possible - is often fraught with uncertainty - you often can't be sure of the right way to do things.
    But for the interpolation filter in a DAC there is absolutely no uncertainty - if you want to recover the original analogue signal in the ADC at the point it was sampled perfectly you must use an infinitely oversampled interpolation filter with a sinc impulse response. It is as simple and clear cut as that. 
    The problem is that you can't have infinite oversample, and you can't have an ideal sinc impulse response as this needs an infinite amount of processing - so you have to optimize things to suit the processing you have, and this is where lots of optimizing with careful listening tests come in. But the point I am making is that the closer you get to the ideal, the more accurate you can make the reconstruction.
    There will come a point where if you increase the oversampling rate and increase the tap length and you will hear no sound quality changes - in short its as close as it needs to be to the ideal - but we categorically have not reached that point yet. That's what is so amazing about how sensitive the ear/brain actually is whilst playing back music. And from a measurement POV we are a long way away from an ideal interpolation filter too - you would need about 100,000,000 taps, or an FPGA that has 100,000 dsp cores (Mojo has 44 dsp cores) for it to measure perfectly. Of course Mojo from a measurement interpolation filter POV measures much closer to the ideal than any other non Chord DAC I have ever seen - at any price point.
    Anyway, getting back to your question - a sinc impulse response is linear phase, with a fixed group delay, and so is Mojo's WTA interpolation filter.  
    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/
    Traveller likes this.
  11. Arpiben
    Thanks Rob.
    In short terms should I understand that brain is also sensitive to phase transients?
    In fact it was more my concern rather than a group delay value correlated to samples and in principle steady as per filtering point of view.
    As  a newbie in digital audio, I recently tried some DSP software (not on fly)  with minimum phase delay option. In some cases it improved SQ except for vocals where it add some artefacts (nasal). I guess the best will be to apply a shifting digital impulse to those DSP filters in order to have some clues.
    Rob I also didn`t forget that it is preferable to let do Mojo do all the interpolation job.
    Gratefully yours,
  12. GreenBow
    Absolutely. Thanks for reminding by describing its sound signature. (I remember once saying, the Mojo is beautifully balanced to someone asking about it.)
    I have said to people that the Mojo is a brilliant DAC if you can live with its foibles. (For desktop use or otherwise.) Like being warm/hot, or like on the USB port where it needs software to insert a second's silence. Note: it was great to learn that it works flawlessly from PC on optical though.
    Thank you for getting in touch. I remember getting on really well with you on your Mojo review.
  13. rkt31
    i think ferrite cores are not suitable for analog signals. i tried the small cores on my headphones and it caused the sound of mojo too soft sounding . it lost the treble detail. ferrite core on analog signal will act as low pass filter. even i found that these core though are very useful for digital transmission but if you use more than one core very closely spaced, the sound even through digital transmission is affected . this is my perception. so imho use more than two cores on digital cable spaced apart, preferably at both ends. 
  14. maserluv
    Hi guys,

    Which brand of optical toslink did Mojo Designer prefer? Or did he mention?

    Regards Wayne
  15. onsionsi
    I got Mojo about one month ago and really interesting to using it with my SE846 and HD800S.
    In fact i can't now listen to the music without it.
    I will not talking about my impression as i'm sure there were a better reviewers gave a professional review here in this forum.
    But my question here, while i plugged Mojo to my laptop by using Jriver MC21 i got a vastly better result than what i got it when i plugged it to my iPhone by using the Apple music player or even the VLC media player.
    I will try another player in my iPhone like HF player and i will post my impression here as soon as possible.
    Any thoughts will be appreciated.

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