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

Discussion in 'Portable Source Gear' started by Mython, Oct 14, 2015.
  1. KaiFi
    Is there any way to run the Mojo off of USB power?

    I really like the Mojo, it's the best-sounding DAC I've ever used, but the fact that it runs on battery and I have to charge it is annoying to me because I really only listen to music sitting at my desk. If I charge it all the way and then run it with the USB cable plugged in, it is still running off the battery?
     
  2. RiseFall123
    I never had iPhone noises even if I stick the Mojo and the iPhone together. It’s not the Mojo but is the hp in fact I had shortly the Denon MM400 and it had this issue. My all other hps no issues at all.

    Many people use as stable dac for desktop rig, doing that, it will reduce certainty the battery lifetime but it’s the only way to avoid the charge boring routine.
     
  3. miketlse
    There is quite a bit of info in the FAQ in post #3

    Quote:

    If you fully charge Mojo then use it in a desktop it will not switch off; the power dissipation that the charger uses in matching the current drawn by Mojo is negligible. You are only at risk when charging and using at red ....

    Just to give you some numbers - fully charged and matching Mojo's current draw the power dissipation is 107 mW for the charger circuit. That will increase running temperature by less than 1 deg C. But at flashing red it is 910 mW for the power dissipation in the charger.

    Now I could fix this by using a switcher based charger rather than a linear one - but these inject too much RF noise onto the battery. This would impair sound quality, and Mojo's design goals was that plugging in the charger would have no significant change in SQ - which would not happen if I used a switcher based charger. I am not prepared to damage SQ as to me this is the most important aspect just for a tiny improvement in usability.

    Rob

    To understand it better, let's assume Mojo is off and charging.

    Now the charger has two modes of normal operation - constant current, which is set to 330 mA, and constant voltage which is set to 8.200 V. Now when the non charging battery battery voltage is less than 8.200 V, then the charger supplies a constant current. But when the non charging battery voltage gets close to 8.200 V, then the charger switches mode to constant voltage at 8.200 V. The current that is charging the battery then slowly falls from the initial 330mA, to zero - its in the trickle charge mode now. Eventually, the non charging battery voltage hits exactly 8.200 V, the charger is in constant voltage mode of 8.200 V, no current now flows into the battery, and the charger switches off automatically. When the battery voltage falls to 8.0 volts, then the charger will return to charging. Tip - if you want to force the charger to top up Mojo's battery to 8.200 V then removing the charge USB, wait 5 seconds, reattach, and the charger will top it up to 8.200 V.

    Now imagine that Mojo is on at the same time as it is charging. In this case, the battery will continue to charge until it gets to 8.200 V, and the charger is set to voltage mode and gives 8.200 V too; so no current flows into or out of the battery; but Mojo itself is drawing 180 mA of DC current, and this will simply come from the charger - so the charger will supply the needed 180 mA for Mojo. It will do this for ever, and it won't switch off. This is intended, as it means that the battery is effectively not being used to supply the bulk of the current, won't charge or discharge, is held at a safe level, and will operate like this for a very long time.

    Now we have been talking about DC currents, and this is indeed the vast bulk of the current. But what about dynamic currents and noise? Because the output impedance of the battery is much lower than the charger, then the noise of the charger is reduced; also dynamic currents still comes from the battery. So running in this mode ensures the best of both worlds - low RF and audio band noise from the battery, large dynamic currents available, and low PSU impedance too - but without the worry of the battery wearing out from charge and discharge cycles.

    I hope this clarifies.

    Rob

    Quote:

    when the Mojo is being used and being charged especially when driving lower impedances there is a net drain on the battery. This means that the charging circuit does not quite provide enough power to power the Dac and amp circuitry and keep charge the battery at the same level this is because we had to limit the amount of charge over a given time due to thermal constraints. Our charging time with the Mojo switched off is usually four or max five hours this is a little inconvenient but when we compare this to other Dac amps that need up to a full twenty four hours to charge we feel that we didn't do such a bad job.
     
    RiseFall123 likes this.
  4. swiftytoenails
    I only use my Mojo connected to my Galaxy S7, but I thought it was broken because of all the RF noise particularly with iems. It got to the point that i bought an ifi nano idsd black label to replace it. Should have just read the forums first because all I had to do was put my phone into airplane mode. The RF noise has completely disappeared. This little device, at least to my ears, is the best portable investment I've ever made.
     
    lwells likes this.
  5. RiseFall123
    I never had RF noise from mojo with iPhone and 3g or lte on with my headphones expect for the denon mm400.
     
  6. IamMathew
    Can it be used some other way than as a DAC? :xf_eek: :xf_eek:

    What about Aeon Closed back? Can you say how big are improvements between Hugo 2 and Mojo with these? Oh, have you also heard the open version of those?
    Thanks :wink:
     
  7. IamMathew
    Mojo is class A, I guess? Through entire volume setting range or up to which color setting (= voltage)?
    So basically, it doesn't matter how loud I push it, it still draws the battery all the same for all the volume settings?
     
    Last edited: Mar 3, 2018
  8. x RELIC x Contributor
    It depends on the load. A low impedance load (headphone/IEM) will draw more Current and drain the battery faster. A high impedance load will draw less Current and drain the battery slower. Also, if using more power to push louder volumes then the battery will drain faster.
     
  9. lwells
    I’m nitpicking. Besides the RF noise, I can’t find many faults with the mojo. And you’re correct, airplane mode solves it.

    I sampled an iDSD BL nano for a week before I bought the mojo. I REALLY liked it. It broke and I sent it back to iFi.

    I was a bit terrified that I would have buyers remorse getting the mojo as it costs 2x as much. I have none. To my ears, they are in different classes.

    For $200, I would take that nano over anything less than the mojo that I’ve heard though. It’s really great.
     
    swiftytoenails likes this.
  10. swiftytoenails
    I bought both of my units used and saved some money, but I did pay close to retail for the iFi. There was no RF noise at all with the iFi and the sound was eerily close to the Mojo to my ears. I would have been happy with either, but once I figured out how to eliminate the RF when using the Mojo, the choice was clear as to which one was going to stay.
     
    lwells likes this.
  11. ubikutz
    Anybody? :)
    Please help!
     
  12. miketlse
    The default advice is not to try enhancements to the music data that you are sending to the Mojo, but instead focus on sending bitperfect data.
    The exception would be if you want to try using frequency equalisation, in order to cure issues with headphone or room respons.
    Are you using the Chord driver?
     
  13. ubikutz
    Co
    Hi!

    Thanks for the reply. 100% agree with your advice for music content.

    For games i have some challanges as the conent is often harsh and tiresome.
    I found that i need to tone down the highs a bit (eq) and tone down the dynamic range (equalize loudness) so that i dont get ear fatigue with headphones even at low volumes.
    Battlefield 1 for example has brilliant sound design but there’s only so much explosions and gun shot sounds my ear can take.

    This is why i’m trying to understand how/if i could apply eq and loudness equalization to the mojo when the content requires it.

    I dont have the mojo yet so no way for me to check if these options are available in the enhancements pane. Could you help me out with a screenshot?

    Do you know a better way to achieve these goals.

    Thanks!
     
    Last edited: Mar 4, 2018
  14. miketlse
    The mojo contains no functionality for frequency or loudness equalisation - it merely accurately converts the digital signal it receives, into the analogue sound output.
    That means that any frequency or loudness equalisation, has to be performed by the PC.
    There are a few posters (especially @JaZZ and @Music Alchemist) who have described in some detail their experiences with equalisation, and the software that they use.
    My suggestion would be to search the Chord threads for some of their posts. You may be in luck, and one of them will reply to your post.
     
  15. RiseFall123
    I use the pair mojo-AFO and the source is iPhone-Tidal.
     

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