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

Discussion in 'Portable Source Gear' started by Mython, Oct 14, 2015.
  1. miketlse
     
    The Mojo is driving an electrical load  (headphones or amp), so no difference up to that point. The difference comes in that the impedence of headphones will change with frequency (they are a mini version of speakers), but I am not sure about the input impedence of amplifiers.
     
    The Mojo is happy driving low impedence phones such as shure SE846 (9 ohms I think) and high impedence phones (eg Sennheiser HD600 and HD800 are 300 ohms).
     
    beyer offer some headphone families with different impedences, eg the DT 770 pro is available at 16 ohms, 32 ohms, 80 ohms, and 250 ohms). With this design strategy, phones are basically the least impedence model, with an inline resistor added either in the headphone lead or the earpiece. Why all these versions of basically the same headphone? Firstly the 16 and 32 ohms are easier on the battery life of mobile phones, but this must be balanced by the fact that as the impedence increases, the control over bass notes improves - so it is swings and roundabouts.
     
    But this is digressing from the Mojo, I am sure that I saw posts by Rob Watts that state that higher impedence headphones draw less power than lower impedence models, but I cannot find them yet.   
     
    Traveller likes this.
  2. Rob Watts
    Strictly speaking there is a difference - the impedance of headphones can be reactive, so there could be a phase shift between current and voltage, thus slightly increasing power drain. But don't worry about that. The max power being drawn within Mojo is with 8 ohm IEM's - as although the power in the load is low, the current is higher and that will increase power dissipation on Mojo's discrete OP stage, even when you are running say at red on the volume.
     
    Oh another point - power loss within the battery is 0.2% of Mojo's total, so it is insignificant.
     
    And another one - power loss whilst charging is because of a use of a linear charger - so when the battery is fully depleted, we get max power loss in the charger, and very little power loss whilst at the end of the charge cycle. Why do I use a linear charger and not a switcher based charger? I have yet to find a switcher charger that allows full RF filtering, so it will upset the sound quality whilst charging. My design goals were to have no loss in sound quality whilst listening and charging and going to the current range of switcher chargers won't do that.
     
    Should you find the thermal trip operating whilst charging and listening, then as a poster recommended, putting Mojo on its side fixes that possibility.
     
    Rob
     
    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 and miketlse like this.
  3. miketlse
     
    Oh dear, prepare for incoming questions from iOS 10 beta users.
     
    http://www.head-fi.org/t/702787/chord-hugo/13560#post_12750581
     
  4. Rowethren

    Nice information! So which linear usb power supply do you use?
     
  5. Traveller
    Thank you very much for your time and info gents![​IMG]
     
    Rob, I'm sorry, I don't understand the point about the 0.2% battery-loss... should I understand it to mean that this is the total cost of actually driving any headphones and that the remaining 99.8% processing (DAC)? [​IMG]
     
    Mike, thanks for pointing out what is certainly a basic principle of impedance vs. FR but I was not aware of the direct affect (of impedance) on LF and bit now I am much appreciated  [​IMG]
     
  6. Mojo ideas
    Guys we at Chord really did extensive studies into batteries before we chose the optimised solution we have in Mojo. We even looked at up and coming battery technologies like lithium sulphur which potentially could extend Mojo's playing time by a factor of four but unfortunately the newer chemistry's are just not there yet. Be aware the battery technology we've chosen is good and above all its safe being a higher spec than most. Remember that mojo is designed for a pocket or a hand to carry and a poorly deigned lithium ion battery could be chemically very volatile. Look up lithium batteries catching fire I don't want one of those in my pocket!
     
    Mython, x RELIC x and miketlse like this.
  7. Rob Watts
    The 0.2% is the power loss due to the battery supplying the current that Mojo needs. So its the power loss within the battery itself and is negligible compared to the power loss of USB, FPGA, oscillators, discrete DAC and OP stages, references, power regulation and charging. All these things had to be heavily optimized during the design phase.
     
    Rob 
     
    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.
  8. Mython Contributor
     
     
    So, if I'm understanding you correctly, DAVE was easy to design, since it doesn't need to worry about battery duration. Is that correct, Rob? [​IMG] 
     
  9. canali
     
     Rob: a brief aside, but revisiting something we touched upon last week:
    the new module coming out this or next week: will an accompanying case be offered at the same time?
     
  10. audi0nick128

    Hey Rob,

    Did you try a high quality SMPS, like an Ifi Ipower? Oh and while we are at it, I read somewhere that the power supply being used to load a battery can have influence on the batterys performance. What do you think about that?

    Cheers
     
  11. howdy
    I've tried everything, this phone definitely does not have USB out. Does you or anyone have a list of cellphones with USB out so I can narrow my search. The goal is to buy the cheapest Android device with USB out so I can use my Tidal offline with the Mojo.
    Thanks in advance!
     
  12. canali
    ipod touch 6   64-128gb..no, it's not android (and i have an android phone)
    but imo a good gizmo to easily synch up w the mojo, dragonfly for tidal hifi (using senn's captune app even) 
    btw, i thought you were getting an ipod touch6
     
  13. Mython Contributor
     
    Did you read the 'connecting Mojo to MicroUSB devices' section of post #3?
     
    It doesn't contain all the answers, but it does point you to a USB issue discussed recently, in this thread (error initialising USB system), as well as pointing to the compatibility list for USB OTG smartphones, on the UAPP homepage. That may get you nearer to finding an answer, and if it doesn't, then it may be that your phone simply isn't USB OTG compatible, or perhaps some other reason, but please check the aforementioned and see how far it takes you.
     
     
     
    EDIT: good catch, @ canali - I overlooked the offline part of that question, as I was focused upon the USB connection aspect.
     
    @ Howdy: Tidal offline content is encrypted and UAPP can't access it offline, which means, amongst other things, that you can't play Tidal offline, bit-perfect, to Mojo
     
  14. howdy
    Yeah I did read post 3 about it which helped me get where I am and have concluded that the phone I bought for the mojo is just to cheap and does not have the USB out. I do have a OTG and still did not recognize it. I may just have to go with what I know works which is Apple. I have a IPhone 5s but it's only 16gb I would be happy with a 64gb iPod touch. My Onkyo DP-X1 hooks up nice with mojo but I don't what to use those 2 together. I have an OCD where I have to have a dedicated source.
     
  15. miketlse
     
    OTG cables are directional (one plug has 4 pins, the other has 5) so the correct plug must be inserted into the phone - try reversing the cable, and seeing if that improves things.
     

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