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Chord Electronics Qutest DAC - Official Thread

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  1. HumanMedia
    Apologies, the response was mainly for the original poster ayang02 and the other poster using the default midi tools in macOS.
    And the ‘isolation’ in galvanic isolation is not isolation from noise but isolation of electrical current via a magnetic field in a transformer. if you are lucky it will give you maybe 40 or 50db noise attentuation across a certain frequency range. Low level noise in the signal will get transferred just like the signal is transferred, some high frequency noise is attenuated and other high frequency noise capacitatively couples across the windings. The better USB decrapifiers will do a lot better than this. There are many many fantastical assumptions about galvanic isolation on forums such as this and I think the misinterpretation of the word isolation Is where it comes from.
     
    Last edited: Mar 11, 2019
    ayang02, Arniesb and Triode User like this.
  2. Arniesb
    Absolutely agree. Tried 2qute which have same galvanic isolation as Qutest with simple usb cable then with Wireworld Starlight 7 usb then Wireworld + Ifi nano usb 3.0
    2qute with simple usb cable is no comparison to Ifi nano usb 3.0 + Wireworld Starlight 7... With just simple cable it sound much less 3rd, much more fatiguing, less lively, less extension in bass and highs. I would imagine Just how much more it can improve with Sotm Usb Ultra...
    Anyone who think that any chord dac is immune to usb problems is delusional... Better use Optical if you want to save money.
     
  3. betula
    That's true for the 2Qute. Much less for the Qutest for whatever reason. I found the iFi iPurifier 3 improved clarity a lot on the 2Qute. Did nothing to Qutest.
    It also depends on the noise level of your system I guess.
     
    Baten likes this.
  4. Arniesb
    Very interesting. My dealer even said that Dave benefits greatly from these decrapifiers. I heard Dave, but it was with Optical input though.
     
  5. OctavianH
    I think the effects are also depending on a lot of other factors. For example, I tried the 1st gen of iPurifier on Qutest and had to remove it quicly since it sounded much worse that without it. Then I had the chance to try an ISO Regen and the same situation. The after some time I changed the interconnect cables (so output to the amp, not input) to some better ones (with much better isolation) and only by curiosity I mounted again the ISO Regen and now the improvements are there, and the sound from USB is much closer to the one I have on the optical input which is connected to a CD transport. Which I would say can be considered a reference. But there is another problem I'm facing, since Qutest is always powered on, from time to time (for example if I shut down the PC during the night and restart it in the next morning) the Qutest is not seen in the USB connections. It seems the ISO Regen hangs and I have to reboot it to fix this problem. More than this, the ISO Regen becomes quite hot during playback, and it is not getting completely "colder" in idle, so I guess it has some idle power consumption.
     
    Last edited: Mar 11, 2019
  6. Baten
    Of course, it makes sense for him to tell you that..
     
  7. Arniesb
    Why? You can just compare inside of the any chord dac vs complex usb decrapifier and easily see the difference. Good solutions cost a lot and takes more space which result in more expenses for casework. Nothing is perfect.
     
  8. Baten
    But good solutions for what? What needs a 'solution'? As mentioned above the 2Qute vs Qutest, the latter already has very good power filtering, jitter rejection, ...
    There is next to point getting an additional decrapifier. There is no crap. None. Like @betula says the iPurifier3 for example does nothing with it. Why spend $300 or more on nothing??
    And if you are really OCD about 'nasty' power, just simple toslink provides absolute galvanic isolation.

    I just don't understand why people would attach crazy audiophile gizmo stuff on something that is already properly engineered. At ~$1800, I'd expect it to..
     
    Last edited: Mar 11, 2019
    bikutoru, OK-Guy and Deftone like this.
  9. Macaron
    Hi,

    Had great improvement on Qutest with an Allo Usbridge, same improvement using the Usbridge on the M Scaler compared to my fanless PC (hdplex, ssd....).

    I had the iPurifier 2 on the Qutest before trying the Usbridge, the Usbridge is far more better for a little more money.

    Galvanic isolation helps but didn't solve all the issues with USB connection and noise. Try it yourself, you'll be surprised.
     
  10. jwbrent
    Thank you for clarifying galvanic isolation and its purpose.
     
  11. Rob Watts
    Qutest is isolated, and you are correct in that the term galvanic isolation historically implies transformers but actually does not mean solely transformers at all; however the actual implementation in Qutest is not via transformers, as the isolation via transformers is, as you state, inadequate. It is actually with high speed RF digital isolators; the reason I use the term galvanic isolation is simply that people are familiar with that term, and is de facto implied that it is completely isolated from low frequency noise - with completely seperate grounds - which this categorically is, plus effective isolation at RF, as the coupling capacitance from the USB to DAC is only 2pF in total across the isolating device. No competent designer in their right minds would employ transformer isolation, as this is inadequate.

    Indeed, looking at the Wkipedia page for galvanic isolation we get:

    "Galvanic isolation is a principle of isolating functional sections of electrical systems to prevent current flow; no direct conduction path is permitted.[1] Energy or information can still be exchanged between the sections by other means, such as capacitance, induction or electromagnetic waves, or by optical, acoustic or mechanical means.

    Galvanic isolation is used where two or more electric circuits must communicate, but their grounds may be at different potentials. It is an effective method of breaking ground loops by preventing unwanted current from flowing between two units sharing a ground conductor. Galvanic isolation is also used for safety, preventing accidental current from reaching ground through a person's body."

    The page then goes on to state the various ways of achieving galvanic isolation and these are: transformers, opto-isolators, capacitive, Hall effect and magnetoresistance. The isolation used in Qutest is similar to opto-isolation, but offers lower propagation delay, lower coupling capacitance, and better skew characteristics than opto-isolators; the process involves modulating an RF carrier in the GHz region, which is picked up internally by an RF receiver.

    Surprisingly, the device I use has lower coupling capacitance than opto-couplers; but of course we still have a coupling capacitance of 2pF. That may not sound much, but at GHz frequencies it becomes significant. So to ameliorate that issue, extensive GHz isolation is performed with chip ferrites and capacitors designed for GHz isolation, so that Qutest is effectively isolated from DC to many GHz frequencies.

    So you are fundamentally incorrect in suggesting that Qutest has only 40 or 50 dB of isolation; moreover USB devices will not improve the isolation, but will actually degrade overall performance as overall system RF noise levels will increase due to the unnecessary circuitry being added.
     
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    bikutoru, Anaz, Triode User and 7 others like this.
  12. OK-Guy
    firstly you have to understand that snake-oil improves your hearing, you progress from there, kapish :wink:
     
    Baten likes this.
  13. Paul Bjernklo

    These 2 previous posts of mine may help re optical cable suggestions;

    https://www.head-fi.org/threads/chord-electronics-dave.766517/page-868#post-14804287

    https://www.head-fi.org/threads/chord-electronics-dave.766517/page-869#post-14809348
     
    Last edited: Mar 11, 2019
  14. HumanMedia

    @Rob Watts Huge thanks for more information on how the Qutest filters noise.

    My bristling at the mention of galvanic isolation is a response to the widespread assumption that just because a device has this on their features list then the device is impervious to USB noise when in the vast majority (all?) cases it isn’t.

    My comment on 40-50db was for a generic transformer, I actually assumed that the Qutest employed quite a few tricks to reduce noise and went well above and beyond a simple transformer. Again really welcome your reassuring details.

    Also agree that poor decrapifiers can make the sound worse. And if some actually add noise, and that this noise ‘makes the sound worse’ then noise is still an issue? Which suggests that the Qutest is not impervious to incoming USB noise? Part of my previous point was that reducing noise before it gets to the dac is better than assuming it is all removed at the DAC. Ideally this means a lower noise source however general purpose computers are high noise sources.

    A better suggestion from myself and perhaps an easier solution than finding the gems in the wide range of decrapifier products is to get a lower noise source. Personally I use a Sonore UltraRendu. Anecdotally the Intel NUCs are even better. The ultraRendu is audibly better than my macOS computer over USB.
     
    Last edited: Mar 11, 2019
  15. Ragnar-BY
    @Rob Watts

    Rob, can you help me with advise, please?
    Right now I have Chord Qutest with Violectric V200 headphone amp. I do like both amp and DAC, but thinking about an upgrade. The obvious way would be to buy Chord TT 2 + M Scaler, but I can`t afford both right now. Would it be better to buy M Scaler for my Qutest, or I should change Qutest for TT2? I tend to buy M Scaler, because it is an interesting new technology and I`m actually quite happy with my V200 amp. But maybe I underestimate how good TT2 is? What improvements could be expected from one or another upgrade?
     
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