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Chord Electronics Qutest DAC - Official Thread

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  1. Ragnar-BY
    Thank you for clarification. I assume further questions should be asked in a TT2 thread.
     
  2. Jon L
    In the spirit of more direct connection, I have now managed to get rid of both USB cable and spdif cable from my digital setup. CAPS v.3 server->USB A-B adapter->DXIO usb-spdif converter->RCA to BNC adapter->Qutest.
    I can say two things: I no longer need Qutest's "Warm" filter; It can be depressing to be able to compare a cable with "no cable."

    [​IMG]0313191326 by drjlo2, on Flickr
     
    Ragnar-BY likes this.
  3. Qute Beats
    no cable is the best cable. Now, how short a USB cable could you use there and how would it compare I wonder? Since isn't this set up still USB based as in USB from PC, so does not USB-USB do away with the converter?? Just curious as those SPIDF boxes are expensive.
     
  4. ATXKyle
    The UpTone Audio USPCB is another way to get rid of the cable via the USB. It’s cheap and for me sounded better than my expensive Curious USB cable. Trick is dimensions ... it’s short so your streamer/server USB out has to sit very close to the DAC USB in.
     
  5. Qute Beats
    just had a look at that, interesting, though certainly is short.
     
  6. Jon L
    I just tried to order the UpTone USPCB and it was over $40 after tax (CA) and cheapest shipping option. :triportsad:
    The USB adapter I used has even shorter signal path and is sturdier, and it comes free in the box of original UpTone Regen, which many of you probably already have...

    [​IMG]REGENadapter by drjlo2, on Flickr
     
  7. OctavianH
    Anyone had the change to compare ISO/USB regen with the JCAT?
     
  8. Baten
    JCat is just an intona in another casing. Maybe you can find comparison between regen and intona more easily
     
    OctavianH likes this.
  9. OctavianH
    As far as I knew Intona was just providing isolation, the ISO Regen and JCAT are also reclocking. Maybe I am wrong.
     
  10. Baten
    Jcat/Intona is the same technology :) both reclock the usb data stream.

    From Intona:
    The 7054-based USB Hi-Speed Isolator is a phy-level receiver/isolator/reclocker/repacketizer working at a bidirectional bandwidth of 480 MBit/s.
    It receives and transmits USB data using a dedicated ULPI-transceiver, buffers and translates by our proprietary logic using FPGA technology and isolates using industry-leading RF-type isolators by Silicon Labs with least possible capacitance.
    It does not translate or distort data packets like a hub but does reproduce and reclock the original data by 100%.

    Is there any customization possible, for example using a better oscillator?
    What would you expect by using a “better” oscillator?

    We measured 12.5ps of RMS jitter on the USB packet clock. A more or less jittery oscillator would not make any difference on this, because of the very low tuned lp-filter in the transceiver’s PLL.

    We use four clocks in our design, all shifted slightly in phase and affected from natural spread spectrum of the isolator chips and other sources. This really helps to bring EMI down and to spread current peaks – e.g. to lower the packet noise.
    If we would tune everything inside to least jitter, this would rise packet noise and also EMI radiation.

    One need to distinguish between

    • sample clock in an ADC or DAC: low jitter is the most important, because only the right sample at the right time is the right sample
    • transmission clock of a serial system: BER (bit error rate) or eye mask to be specified
    • clock passing integrated logic: setup and hold times to be met
    We decided to go for low noise, so spreading clocks and accepting inter-logic-skew was the way to go. Further, clever design of return currents and also a good and low impedance decoupling network of the power supplies are by far more important to meet your needs than looking for the oscillator.
     
    Last edited: Mar 14, 2019
    OctavianH likes this.
  11. STR-1
    I’ve used both USB adapters, and the USPCB is clearly better. For those you have the USPCB and haven’t tried this, do try with the 5v power switched off when used between the source and USB regenerator (e.g. ISO Regen). It sounded even cleaner in my system.
     
    Last edited: Mar 14, 2019
  12. OctavianH
    I tried this and had a problem. When Vbus was OFF on the USPCB the Qutest was not seen on my PC. Are you able to use Qutest via USB with Vbus OFF?
     
  13. STR-1
    I do not have a Qutest. Using either DAVE or Hugo TT 2 as the DAC, both of these need the 5v on the USB input for handshake purposes. I assume this is the same for the Qutest. So if I am running USB straight from my Innuos Zenith SE server to the DAC, 5v must be switched on (actually the USPCB is too short for me to use as a connector in this configuration, but it would be the same for any USB cable). However, if I use a USB regenerator between server and DAC (I have both ISO regen and tX-USBultra - currently using the latter) I can switch 5v off between server and regenerator, as long as 5v is switched on between regenerator and DAC.
     
    OctavianH likes this.
  14. miketlse
    To reinforce what @STR-1 posted, the chord dacs tend to use the 5V VBUS to indicate that the USD data port is active.
    If the VBUS reads 0V, the data port is identified as inactive, and then switched off. This will be the point at which your PC can no longer see the Qutest.
     
  15. Jon L
    So Chord DAC's are unlike some DAC's that only require 5V VBUS for initial handshake but will keep on working if 5V is turned off later?
     
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