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

Discussion in 'Portable Source Gear' started by Mython, Oct 14, 2015.
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  1. georgelai57
    Now that I've seen The Holy Grail a.k.a. white DSD light on my Mojo, I doubt I'll continue to use it that way. Except once in a while just for fun.
  2. Hawaiibadboy Contributor
    That 10th guy...[​IMG]
  3. Rob Watts
    I understand those concerns to - after all the data is the same. But there are solid scientific reasons why they can make a difference.

    In the 1980's, people started talking about mains cables making a difference to the sound quality - and I didn't believe it either - particularly as my pre-amp had 300 dB of PSU rejection in the power supply. But I did a listening test, and yes I could hear a difference. Frankly I still could not believe the evidence of my own ears, so did a blind listening test with my girl friend. She reported exactly the same observation - mains cables did make a difference to SQ.
    To cut a long story short, I proved the problem was down to RF noise. RF noise inter-modulates with the wanted audio signal within the analogue electronics, and if the RF noise is random, then the distortion is random too and you get a increase in noise floor with signal. This increase in noise floor is noise floor modulation, and the brain is very sensitive to it; you can perceive tiny amounts of noise floor modulation as a brightening or hardening of the sound. By tiny I mean the noise floor modulation needs to be well below -200 dB, so the brain is very sensitive to it. With the right test equipment, you (APX5555 is only test equipment that has no innate noise floor modulation) can easily measure the effect.

    The RF characteristics of the cable can change the RF noise that gets injected into Mojo's ground plane, and this is the mechanism for changes in smoothness. You may say why can't you make it insensitive to it; well I go to silly lengths to RF filter and decouple, and use dual solid ground planes on the PCB, but you can't remove the problem. For Dave, Hugo TT and 2 Qute I have galvanic isolation, and this eliminates the problem (along with other SQ problems such as sound-stage depth). But I can't do this with portable devices, as it draws power from the 'phone. That said it's less of an issue with portable electronics as they are less power hungry and create less noise.


    So what are the best USB cables? Firstly, be careful. A lot of audiophile USB cables actually increase RF noise and make it sound brighter, and superficially impressive - but this is just distortion brightening things up. Go for USB cables that have ferrites in the cable is a good idea - it may also solve any RF issues from the mobile that you may have too.



    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/
    onsionsi, Pokemonn, masterpfa and 3 others like this.
  4. LouisArmstrong
    How do you put DSD file into iPhone? I thought iTunes doesn't allow it?
  5. tkteo
    Dear Mr Watts,
    if there is a "Rob Watts approved" list of USB cables, I am sure I am not the only Chord DAC owner who would love to know what this list comprises.
  6. Roybenz
    Im using iphone 6s, with tidal. How would mojo compare to oppo ha 2 and the larger oppo ha 1 or the Hugo?

    Using the audeze Lcd3f
  7. salla45
    Sorry Im not savvy enough to advise, but sticking my necking i would say it's more likely that your 4 pole cable is set up to take  a line out + coax signal to just coax RCA type. Rather like the freebie I got with my Fiio. I think you need something like this, but I'm sure there are cheaper options.
    A fellow member on HeadFi did my cable for my fiio for a fraction of this, and it works great!!! If you get stuck, Ill put u in touch.
    Angular Mo likes this.
  8. equedadoii

    i can understand not wanting to play favorites,
    however, i wouldn't mind this list either. :)
  9. Rob Watts
    I promised some time ago that I would show some measurements showing Mojo's performance. My reasoning for this was that Mojo does things that no other (non Chord) DAC does at any price; I was kind of annoyed that some people were comparing it to $100 DACs when the true competitors were $100K - and I kind of get that, its difficult to take Mojo seriously given its size and price. But if you could see the design complexity that goes inside Mojo then one could appreciate how much better it is; it really is vastly more complex than other DAC's, and this complexity is needed to recreate the original analogue signal accurately.
    But I can show you that something special is going on from measurements. Take a look at this plot. This is a FFT of a 1kHz output at 2.5v RMS into a 300 ohm load (blue trace) and then with no signal (red trace):
    Now what is very interesting is the noise floor at -175dB - it does not change at all with 2.5v or nothing which indicates a complete absence of measurable noise floor modulation. Noise floor modulation is extremely important subjectively - you perceive the slightest amount as a brightness or hardness to the sound. When it gets bad, you hear glare or grain in the treble. All DAC's (apart from Chord DAC's) suffer from measurable noise floor modulation - typically the noise floor would be -160 dB with no signal, and -140 dB at 2.5v RMS. Some Class D amps are awful with noise floor at -120 dB (one reason why Class D often sounds so bad).
    To get this measurement is a massive challenge, as ADC's themselves have large amounts of noise floor modulation, way bigger than my DAC's. The only test instrument that has noise floor modulation that can actually measure Mojo's performance is the APX555. This uses a novel approach to solving the issue - 4 ADC's and an analogue notch filters. The outputs are combined in the digital domain, so this means one ADC is handling the fundamental sine wave, another ADC looks at the noise via the notch filter. So you will only be able to measure Mojo's true performance using the APX555. 
    Many posters have commented on how smooth and musical sounding Mojo is - and its in part down to the absence of measurable noise floor modulation. Actually getting this performance is very complicated, as within the DAC there are a enormous number of mechanisms to create noise floor modulation. One reason why its taken me 20 years of DAC development to do it!
    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. tkteo
    A list sorted in alphabetical order. Then again brands with "A" as first letter of brand name would be the happiest haha.
  11. Sound Eq
    any companies make ferrites micor usb- otg micro usb, that is ultra short, as the last thing is i will want to add brightness to the sound
    so please help telling which company is making such cables with ferrites 
  12. spook76
    If you are using Onkyo HF Player, you can simply drag and drop it from your music library on your home computer to Onkyo app when you have iTunes open on your desktop.
  13. karmazynowy
    Has anyone tried Mojo with Oneplus X? Does it work without any problems?
  14. imattersuk
    I don't know how many times I have to tell you guys this....... 
    "Reference USB cable is designed to transmit high definition digital audio between USB audio components (such as a computer or storage devicen and a high performance DAC) with ultra low jitter. It utilises a carefully engineered geometry including an integral Ferrite jacket, electrically isolated power conductors and an impedance controlled data lane to reduce timing errors within the digital signal, for cleaner audio transmission."
    All I keep hearing on this forum is I want cheap cheap cheap, well you get what you pay for, simple really. 0.3M is as short as you will get if you want a ready made well built cable with a Ferrite jacket unless you can get someone to make a custom cable for mucho $$$$$
  15. RamblerBoy

    thank you for explaining it to me.
    as for the fiio x3ii, i won't be using it anymore and i'll be putting them up for sale online, hopefully not the dustbin because i need the cash, after getting it repaired under warranty. will be using my phone with the mojo else i might get a pioneer xdp100r.
    i wasn't talking about fiio in particular. what about the output from android phones? they are usually connected to external dacs using usb cables right? i'm guessing usb out from the phone to the usb input of mojo
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