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

Discussion in 'Portable Source Gear' started by Mython, Oct 14, 2015.
  1. Mython Contributor
    It is easy to criticise Mojo for getting warm, and (arguably) it may be a legitimate criticism for some people who live in particularly hot climates.
    However, when one realises how much processing power Mojo uses to accomplish its sound quality, the heat dissipation is understandable and excusable, especially considering what a tiny case it is squeezed into.
    (bold emphasis added by me)
  2. RPB65
    Yeah it'll do! [​IMG]
  3. waveSounds
    I like it.
    Maybe I'll get the ol' Arctic Silver thermal paste out and plonk a Nofan CR-95C...
    Traveller likes this.
  4. RPB65
    LOL Reminds me of my PC modifying days! Sounded like a vacuum cleaner by the time I had finished. So annoying it was mental.
  5. miketlse
    will work if you use mojo only for desktop situations.
    For portable use, you must have monster sized pockets. [​IMG]
  6. waveSounds
    Was this yours, RPB? :wink:
    Traveller, aangen and jmills8 like this.
  7. kvad
    : ) I presume if one wants a slightly less extreme solution one could try something like the Akasa RAM heatsinks.
  8. RPB65

    Hahaha, brilliant. Not quite but the wife was not impressed! 
  9. GreenBow
    Hooray, someone's done it.
    I was banging on about a heatsink ages ago. However I was always stuck at how to hard fix the heatsink on. I figured using a heatsink the same size as the Mojo and strapping it on with strong rubber bands.
    What bothers me is, what happens when the battery gets a little aged and worn.....When using Mojo as a desktop DAC, it's best to leave it fully charged. That allows the Mojo to cool a little while it switches to battery only for periods of time. However once the battery looses 0.2V from full charge the charger starts again. Leaving the Mojo charging and playing - getting hot. Therefor when the battery gets worn with age, will it loose it's ability to hold full voltage. ...Therefor leaving it permanently charging while playing.
    Therefor the heatsink could very well be needed for desktop work, especially in hot climates.
    I remember the post from Rob Watts, saying please leave battery choice us. You can find it in post three. About how Chord are clever, did the thinking, etc and made battery choice. ..However I would actually like the battery statistics and potentially the choice to find a cool running battery.
    I think the battery is designed to be able to provide enough power to drive high impedance headphones. E.g Sennheiser HD800. However while my Mojo is in my possession I doubt I will ever use other headphones than low 32ohm Grado. Long story; short answer is because they are cool on the ears once you go up the range beyond the S-cushion. Plus many models are light, and contrary to opinion I find them extremely comfortable. (It's all about finding the right place for the cups on the legs. http://www.head-fi.org/t/754373/grado-l-cushion-comfort-for-sr225-ps500#post_12461917 )
    Therfor I don't think I need the uber Mojo Chord battery. I might be wrong though because I have not thought the electronics through.
  10. Torq
    Assuming, which I am, that the battery management functions, including thermal management, current/voltage protection and charging behavior are not part of the battery itself but are actually implemented in the Mojo itself, switching to a different battery is not going to get you very much.
    If the Mojo's safety and charging features assume battery stability/safety at a given temperature and use knowledge of safe discharge and charge rates, in addition to temperature sensing, to manage that, and the battery you put in isn't safe at that temperature, you're going to have a real mess on your hands in very short order.  You'll either kill capacity or, more likely, fry the battery and/or start a fire.
    Batteries do not run "hot" or "cold" per-se.  A "low temperature" battery is simply a battery (group of cells) or cell that is only within spec, and safe, UP TO that rated temperature.  It does NOT mean that it runs cool!  While specific chemistries can have an effect on exothermic output for a given load (input or output), the differences are minor and mostly it's going to come down to the battery's internal resistance and current draw/charge rate.
    You can reduce the peak operating temperature by increasing the heat dissipating capacity - for example by adding heatsinks.  Heatsink efficacy is dependent on material (different materials have different thermal conductivity/radiant properties), surface area, COLOR (yes, really) and thermal differential between the heatsink and whatever the heat is being "sunk" into (nominally air, but it could be water etc.).  Provided the medium you're dumping heat into has the thermal capacity to accept it, then generally the higher that thermal differential is (i.e. the hotter the heat sink is in relation to that medium) the better!
    So, you swapping the battery won't make Mojo run cooler.
    Rob could change the implementation so that it ran at lower temperatures (which is still nothing to do with the battery) ... but that would absolutely come at the cost of playing time, and/or charging time, and/or available power (and therefore performance) ... or would need an entirely different chassis ... either larger or festooned with heatsinks!
  11. GreenBow
    I was thinking that the Lithium-polymer battery was the reason it is hot. Meaning I thought maybe it runs hotter that Lithium ion. I don't know though. However I never came across hot battery behavior on any device I own. Does that not make sense. I ask because I do not understand you statement saying another battery would not run cooler. I mean, the battery in the Hugo is cool, so I question your logic. I might be wrong of course, so please don't misunderstand me.
    The Mojo battery certainly produces heat when it charges. However I think possibly the heat when playing (and not charging) might be heat from the battery due to discharge. Therefor it you install a cooler running battery, there will be no cut out issues in hot weather.
    That's why I think it might be an idea to have the physical and electronic specifications of the Mojo battery.
  12. captblaze
    correct me if I'm wrong, but heat during playback might be due to the amp design. Class A amps produce heat when pushed hard and I do believe (once again correct me if I'm wrong) Mojo has a Class A amp onboard
  13. Torq

    The reason you have never come across "hot battery behavior" in other devices is nothing meaningful to do with the battery.  It's about the demands of the device, its ability to dissipate heat, and what thermal management it imposes.  For example, if an iPhone gets too warm it'll first throttle is CPU/GPU behavior down to lower power draw (and thus reduce generated heat) and, if that doesn't get things under control, it'll shut down with a thermal warning message.  By design, it's electronics prevent the temperature from rising beyond a certain point (i.e. the thermal safety threshold of either the battery, or one or more electronic components in the unit).
    You might find a VERY SMALL temperature difference between LiON and LiPo with a good thermometer, if everything else in the system you were measuring were equal.  But it won't be, since the internal resistance of the battery will change - among other things.
    As to Hugo being cooler ... it has a larger surface area, so even if everything else was equal, of course it would run cooler (larger heatsink mass, greater area to dissipate heat from, which, given the same thermal load will result in lower temperatures).  If you put Mojo into the Hugo case, it'd run cooler too (or would, at least, take longer to saturate the heatsink/dissipation capacity of the casework).
    You're missing the physics at work here - and saying "cooler running battery" repeatedly won't change them.  There aren't "cooler running BATTERIES" as such ... just batteries that are operated at lower thermal limits.  No matter what specs Rob gives you, they're not going to change the laws of physics.  And if you want a cooler running Mojo, then you want higher impedance cans (lower current draw, slower discharge rate), or you'll have to persuade Rob to come up with a version that limits current draw/charge rate artificially - which means trading off runtime or performance.
    And all of that ignores the fact that it's not that the battery is generating heat, its that the unit is as a whole ... and that it can operate, safely, at higher temperatures than other devices because it has a battery than can safely survive high-temperature operation.  That's ALL the temperature spec on a battery means.
    Incidentally, there is no issue with my logic ... just your apparent non-understanding of physics, chemistry, electronics and thermal management in modern devices.  You're looking at the wrong things, drawing the wrong conclusions from them and then taking that as the basis for your argument.
    Mython likes this.
  14. GreenBow
    No idea. We were told the Mojo did not incorporate and amplifier. I guess we should take a peek at post 3 gain because it will be there. However as far as I remember there was some mention of an amp later on from Rob Watts. I always assumed there must be some op amp at the output stage to lower output resistance, if needed.
    @Torq I am going to leave this with you, and not reply. I don't have the patience to go through another series of posts back and forth. Feel free to end it how you will.
  15. x RELIC x Contributor
    I honestly don't understand why people can't trust Chord to provide the most robust solution for their equipment. Remember, before the battery was completed the Mojo was an impossibility. Chord had the battery manufacturer research and build a battery specifically for the Mojo over three years to get the power output and the thermal tolerances they have. With the serious computations going on, AND the same power output as the Hugo, AND the small from factor, AND the price, I honestly don't think ANYONE is going to find a better solution than the one Chord has diligently been working toward and implemented with the Mojo. It's not like they just went shopping for a typical Lithium battery (ion or polymer) and threw it in. There was a lot of planning and thought at play here.
    canali, Traveller, Mython and 3 others like this.

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