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

Discussion in 'Portable Source Gear' started by Mython, Oct 14, 2015.
  1. Music Alchemist
     
    Thanks for trying that out for me.
     
    I guess the cheaper DAC/amps are just messing with the sound in a way that makes drums hit harder.
     
    Deftone likes this.
  2. x RELIC x Contributor

    I tried it earlier as well with the DAVE and Mojo and I agree with Rob. While the DAVE has more overall impact across the spectrum than Mojo it didn't specifically raise the bass to levels like you seem to be referencing with other gear.

    A lot of gear is tuned with second harmonic distortion to fatten up the bass. It's common and a lot of people like it but it isn't transparent to the source. Not saying that is exactly what's happening with your case, just a possible answer to your question.
     
  3. GreenBow

    It makes a strong case for shielded cables.
     
    It confuses me at 1.00 minute in where the USB cable is unplugged but the interference continues. Must be picking it up from the short USB cable still on the Mojo.
     
    It would however be interesting to see one of the expensive quality cables on test plugged straight into Mojo. (Without that mini USB cable on the Mojo.)
     
    I am having trouble though working out what it's doing to the music. Meaning is it creating 0s and 1s of its own and distorting the digital signals. Or is it just analogue mush mixed in with the signal out.
     
  4. earfonia
     
    Excellent observation! Thanks!
     
    I agree with you, I shouldn't have used the USB cable when taking the picture of the ifi micro iDSD ground connection measurement. I have checked the micro iDSD USB ground directly without USB cable before taking the picture, so I know that the digital ground is isolated from the analog ground.
     
    As for the short USB cable in the video, I honestly not sure, which is better, to use 2 different USB cables, one for Mojo and the other for micro iDSD, or to use short cable as what I did in the video. I decided to use the short USB cable as adapter and stick with the same cable exposed to the EMI, as I think it is more make sense that way.
     
    Anyway, the measurement was inspired by an 'incident', and was not planned as to test the USB ground isolation. I was measuring Mojo using QA401, to check noise floor, SNR, etc. And I saw the abnormal harmonic distortion during the measurement. Then I learned that those abnormal harmonics came from EMI on the USB cable. I will do more test on this. 
     
    20170201_164927.jpg
     
  5. earfonia
     
    Yes, I also notice that the noise continues for a while after the USB was unplugged. I have no idea why, but the video and the recorded noise sound was not cut or edited. I only add the intro text and picture. When I have the time, I will do more testing with other USB cables, and share it here.
     
  6. music4mhell
    This explains why different USB cables sounds so different with Mojo ..!!
     
  7. Arpiben
     
    You will probably notice also that when USB cable is unplugged what you seem to remove is the high frequency noise part.
    Now is the remaining noise a residual noise or a residual noise added with EMI/RFI only you can tell. Removing also the jumper will avoid it to act as possible antenna for Mojo. 
    Rgds.
     
    Edited:typo
     
  8. earfonia
     
    Ok. I wanted to try today, but after checking all my longer micro USB cable that I have, all are unshielded, as those are mainly meant for charging. I have to buy good micro USB cable with proper shielding to do the test. Will look around.
     
    Btw, anyone with DECT cordless phone at home, could you please try it? Connect your Mojo or any other USB DAC to your PC, and get the USB cable to touch the cordless phone, and try to listen the EMI noise using sensitive IEM. I'm curious to hear other people experience with EMI noise. Thanks!
     
  9. rkt31
    try a good usb cable like this https://www.amazon.com/Oyaide-NEO-Class-Cable-Orange/dp/B003TNFCQW with micro adapter https://www.amazon.com/Audioquest-USB-B-Micro-Adaptor/dp/B00M0H4J6C/ref=pd_bxgy_147_img_2?_encoding=UTF8&pd_rd_i=B00M0H4J6C&pd_rd_r=3NKJ4H06S1Q3HJBCY9R6&pd_rd_w=NmcYD&pd_rd_wg=FRYkV&psc=1&refRID=3NKJ4H06S1Q3HJBCY9R6 . the cable is though more suited  for desktop set up but it easily beats the cheap micro usb cables .
     
  10. GreenBow
     
    I have wondering about getting the QED Reference Audio. http://www.qed.co.uk/hdmi-and-digital/digital-data/reference-usb-a-b-micro.htm
     
    (I don't envy you having to pay out to test though. It would be good if someone could let you use one without having to buy.)
     
  11. earfonia
    Probably the issue is not about shielding, but common ground of USB and Analog circuit. I will look around for micro USB cable with good shielding later. Meanwhile, I have Elfidelity USB ground isolator. It's main function is to isolate USB ground from input to output, and to use external 5V power supply and filter it to provide cleaner 5V DC on the USB output.

    I just did some test, using the same USB A extension cable that I used in the previous video, and a super short USB A to micro B as adapter to Mojo. I've tested that this short micro B USB cable is shielded. Here is the test, fresh from my camera, no post processing at all:




    What I want to see is if ground isolation is effective to block EMI noise. From the test above, it seems quite effective. I've used the Elfidelity USB Booster (that's the name of the gold color device in the middle) for quite sometime. I've tested that It is compatible to all sampling rate as well as DSD up to DSD256. Not sure if it is compatible with DSD512, I don't have the file to test.

    Mojo seems limit the USB handshake to 2 times disconnection. After 2 times, I have to switch it off first to get the USB connection LED ON.

    Please take note, I have no intention to discredit Mojo. I really like it, and it is my go to DAC. This EMI on USB will happen to any USB DAC with common ground, not only Mojo.

    Anyway, let me know what you think.


    I bought the Elfidelity USB Booster here:

    https://www.aliexpress.com/item/Music-Hall-Elfidelity-USB-Boosters-USB-audio-interface-Hi-Fi-Power-Filter-for-PC-DAC-AMP/32397141841.html?spm=2114.13010608.0.0.XAaeHL

    It was less than $50 when I bought it in 2015.
     
    maxh22 and cpauya like this.
  12. Maru10
    Hello,

    Please did anyone here noticed problems with usb data port of the mojo? My first mojo had a problem from day one ( bad connection, would register music source and play via usb only if cable was gently but constantly pushed down near connector), my second unit developed similar problems after two weeks of gentle usage (only at home, haven't travelled with it yet, no accident...). Do we have same sort of bad batch here in Czech?
     
  13. GreenBow
     
    Often people found that was down to the cable. However sometimes it is the port on the Mojo, and some owners had to get theirs replaced.
     
  14. GreenBow

    What's different this time, is that the noise is not present in the Mojo when you unplug the cable. Before it appeared that the short USB cable on the Mojo was making noise.
     
    It does make me think this is what folk who use Jitterbug are doing. Some praise the Jitterbug and if I am not mistaken Rob Watts likes it too.
     
    Thank you for making and uploading these videos. They are eye-opening. I hope you can do more stuff and show, if there's anything left to do.    
     
  15. Music Alchemist
     
    I was asking primarily about how much harder the snare drums hit on the DAVE compared to the Mojo. (Not whether they hit harder at all.) This concerns higher frequencies more than lower ones.
     
    But on the topic of bass, I did also notice that the Mojo actually has less audible bass than many other DACs and amps. It does seem likely that this is more accurate, and that the other ones are exaggerating things because they can't reach nearly the level of quality the Mojo does. I don't want to say that it's harmonic distortion per se, because you can measure that and seemingly all of them are a tiny fraction of a percent there.
     

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