Chord Qutest

[beerandmusic]

19 minutes ago, barrows said:

The point is, reducing noise is exactly what high end audio is about, it is not easy, or affordable to do so.  Same thing with clocks, even a $1500 NDK DuCoLon ovenized clock still has significant phase noise.  everything matters, the more attention which is paid to these details, the better performance gets, but it costs more to do so.

Besides these factors, you have the design of the digital filter(s) and the dAC conversion it self is never perfect, and then you have the analog output section which is also far from perfect.

 

Again, agree here...but at some point there is "diminishing returns", and what is considered subjectively better....

[opus101]

9 hours ago, barrows said:

In the I2S data there are only two things, the data, and the jitter.

 

Since the I2S isn't perfectly isolated, you also have a commonly-overlooked third aspect to consider - common-mode noise currents in the ground wire.

 

Note - these ground currents are by no means a problem for the digital circuitry, they're way below the level needed to corrupt data. But they end up corrupting the analog signal in many cases.

[barrows]

12 hours ago, opus101 said:

 

Since the I2S isn't perfectly isolated, you also have a commonly-overlooked third aspect to consider - common-mode noise currents in the ground wire.

 

Note - these ground currents are by no means a problem for the digital circuitry, they're way below the level needed to corrupt data. But they end up corrupting the analog signal in many cases.

There is no "ground wire" in this scenario.  There is no ground connection from the USB receiver side to the DAC side.  Not sure what you mean?  Of course the "isolation" may not be "perfect", and may have some capacitive coupling.  

In my system, there is no ground continuity between the USB ground, and the ground of the DAC. 

[opus101]

6 hours ago, barrows said:

Not sure what you mean?

 

I was talking about I2S data - there are four wires, three data and a ground. Perhaps I misconstrued your context as you seem to be talking about USB transmission, not I2S transmission.

[barrows]

Nope, I am talking about I2S.  But the ground from the USB receiver is isolated, that is the point.  The I2S lines are:

 

1. data

2. word clock

3. bit clock

4. masterclock

+ground

 

With isolation on the I2S lines, !,2, and 3 come from the USB receiver through the isolators, 4 comes from the clean side of the interface and goes through the isolator to the USB receiver.  Ground is isolated form the USB receiver side to the clean side.

[opus101]

2 minutes ago, barrows said:

 But the ground from the USB receiver is isolated, that is the point.

 

But no isolation is perfect - you'll have some capacitance forming a high pass filter for noise currents. That's why I said 'since the I2S isn't perfectly isolated'. Practical isolation typically has a few pF of capacitance.

[asdf1000]

7 hours ago, barrows said:

In my system, there is no ground continuity between the USB ground,

 

Hey barrows, how? An Intona type isolation method?

 

[barrows]

I never suggested the isolation is 100% perfect, and I have mentioned some capacitive coupling is likely.  That is no reason to not use an isolated USB interface though.

 

Nothing like "Intona".  An isolated USB receiver inside a DAC isolates the USB receiver circuitry and incoming ground of the source, from the masterclock(s), and the rest of the DAC circuitry.  And also allows one to re-clcok the data lines directly from the masterclock, right before they go into the DAC (chip) for lowest possible jitter at the dAC chip (where it matters).

[asdf1000]

48 minutes ago, barrows said:

An isolated USB receiver inside a DAC isolates the USB receiver circuitry and incoming ground of the source

 

Is this part of newer XMOS USB interfaces? Integrated?

[barrows]

No, what I am describing is the commonly used isolated USB receiver circuit for a DAC.  XMOS is just a USB receiver chip, not a circuit.

[asdf1000]

14 minutes ago, barrows said:

No, what I am describing is the commonly used isolated USB receiver circuit for a DAC.  XMOS is just a USB receiver chip, not a circuit.

 

Ahh ok got it, thanks

[beerandmusic]

3 hours ago, barrows said:

I never suggested the isolation is 100% perfect, and I have mentioned some capacitive coupling is likely.  That is no reason to not use an isolated USB interface though.

 

Nothing like "Intona".  An isolated USB receiver inside a DAC isolates the USB receiver circuitry and incoming ground of the source, from the masterclock(s), and the rest of the DAC circuitry.  And also allows one to re-clcok the data lines directly from the masterclock, right before they go into the DAC (chip) for lowest possible jitter at the dAC chip (where it matters).

 

I am seriously considering the marantz ND8006 (mainly for it's alexa capability), but it does suggest it has "some usb isolation circuitry"

 

Optical and coaxial digital inputs as well as a USB-B port enable you to stream music directly from a PC or MAC, or connect other digital sources. The USB-B works in asynchronous mode to support not only 384kHz/32bits high-resolution audio but also the DSD 2.8MHz, 5.6MHz and even 11.2MHz formats for maximized performance and the most direct way to enjoy excellent quality. To safeguard quality when connected to a computer, Marantz built extended isolation around the USB-B input to eliminate the chance of high frequency noise generated by the computer entering the ND8006

[opus101]

8 hours ago, barrows said:

I never suggested the isolation is 100% perfect, and I have mentioned some capacitive coupling is likely.  That is no reason to not use an isolated USB interface though.

 

Right, but I was only talking about I2S, you said you were too. So back to my original statement, you omitted the small matter (and it certainly is small, but not insignificantly so) of the common-mode noise through the I2S connection.

[barrows]

Common to what?  With the isolated interface I am describing there is no continuity (which is not high impedance, if you will) from the USB receiver side to the DAC side.  Not ground, or on any of the I2S lines.

Yes, there may be some capacitive coupling, and this will depend on PCB layout,  but even with some coupling, noise from the USB receiver will be greatly reduced: I am not sure what you are advocating for here.I have described how having a properly implemented, isolated USB receiver, inside a DAC, is an advantage, that is all.  I am not suggesting that it is a perfect cure for all problems of USB, everything matters, and this is just one aspect of a well designed and implemented USB input in a DAC.

 

The sad thing is, even though the isolated interface which I have described is "common knowledge" and has been in use by companies such as Ayre, since the introduction of the QB-9 USB DAC, there are many DACs which still do not use such an isolated interface.

[jos]

I got it...?..., the new Chord Qutest DAC. Last week, directly from England, and it is up and running after a burn-in period for about 100 hour. And the sound is really fantastic in every way, but we all know that already. No reason whatsoever in my opinion to buy a more expensive DAC. Especially not when you have a good integrated amplifier. I'm feeding the Qutest trough my iMac/Audirvana Plus, Jitterbug, Supra USB 2.0 to my USB Regen (with an Sbooster upgrade for the Regen SMPS). From the Qutest to my Yamaha A-S2100 amp and from there to my Revel F208 speakers. I also played the Qutest without the Regen, but I thought it was just a little bit better with the Regen in the chain, but it could be wish-full thinking too, so I am not sure. I also use an Sbooster 5-6V to feed the Qutest. I did not play it without this Sbooster. 

 

I was looking for a new pure DAC and this one fits all my needs. My old DAC, the Arcam iRdac was a very nice sounding DAC too, in every aspect, but this one is simply better in every way, but more expensive too, so it should be better.

[jos]

I am thinking about buying the UltraRendu to improve the sound even further, but wlll that be the case with this outstanding DAC, is the question? Any thoughts, because it’s a big investment too and I doubt it is worth the money?

[ElviaCaprice]

4 hours ago, jos said:

I am thinking about buying the UltraRendu to improve the sound even further, but wlll that be the case with this outstanding DAC, is the question? Any thoughts, because it’s a big investment too and I doubt it is worth the money?

Without a doubt it will.  Just read in this forum what clean power and clocking, of the source streamer, did for the DAVE.  Same will apply to Qutest.  Although I'm more impartial to SOtM s-CLK EX.

[jos]

1 minute ago, ElviaCaprice said:

Without a doubt it will.  Just read in this forum what clean power and clocking, of the source streamer, did for the DAVE.  Same will apply to Qutest.  Although I'm more impartial to SOtM s-CLK EX.

ElviaCaprice, Thanks! I think the SOtM is even a little beter, but I heard it can’t work with Audirvana Plus.

[jos]

7 minutes ago, ElviaCaprice said:

Without a doubt it will.  Just read in this forum what clean power and clocking, of the source streamer, did for the DAVE.  Same will apply to Qutest.  Although I'm more impartial to SOtM s-CLK EX.

In addition: I have clean power and Jitterbugs already.

[ElviaCaprice]

1 minute ago, jos said:

In addition: I have clean power and Jitterbugs already.

Jitterbugs is like a darkage voodoo fixer.  In this thread, many great approaches to Chord DAC source streaming.  

 

[jos]

9 minutes ago, ElviaCaprice said:

Jitterbugs is like a darkage voodoo fixer.  In this thread, many great approaches to Chord DAC source streaming.  

 

Thanks again, I will look into it this evening.

[barrows]

@jos, Glad you are liking the Qutest!  I recommended it to my brother and he is patiently waiting for his to arrive.  I designed a kick ass power supply for his, so he will have perfect power.

I use A+ here streaming with the Sonore Signature Rendu SE, and love it.  I suspect you would have a nice improvement with the ultraRendu and the Qutest.  It is really nice to get the commercial computer gear well away from the audio system.  We recommend the sBooster as a nice, cost effective power supply for the ultraRendu, and you are familiar with those, so all good there.  With the ultraRendu running on decent (sBooster) power you may find no need for any of your USB gadgets, I prefer not to use any in my system, just the best USB cable you can find.

[jos]

18 hours ago, barrows said:

@jos, Glad you are liking the Qutest!  I recommended it to my brother and he is patiently waiting for his to arrive.  I designed a kick ass power supply for his, so he will have perfect power.

I use A+ here streaming with the Sonore Signature Rendu SE, and love it.  I suspect you would have a nice improvement with the ultraRendu and the Qutest.  It is really nice to get the commercial computer gear well away from the audio system.  We recommend the sBooster as a nice, cost effective power supply for the ultraRendu, and you are familiar with those, so all good there.  With the ultraRendu running on decent (sBooster) power you may find no need for any of your USB gadgets, I prefer not to use any in my system, just the best USB cable you can find.

Thanks too, Barrows, but first I will try to sell some stuff; my USB Regen and a few Jitterbugs. By the way: I can connect the UtraRendu in two ways, close to my audio-system with Ethernet and an Uptone USB-connector directly into the Qutest, or about 6 meters away connecting it to the DAC with my Supra USB Cable. In both situations with an Sbooster. Any thoughts about this? Further away will save the cost of an good. Ethernet cable. As a standard I use Supra Cat8 in my house.

[barrows]

Keep the USB short.  At Sonore we use recommend Blue Jeans cable CAT 6A, which is not expensive.  But we are so busy testing things we do not get around to testing high end Ethernet cables.  Most tests I have seen have not usually tested the fancy Ethernet cables vs. a good commercial cable like BJC CAT 6A, but someday I will get around to it!

[jos]

3 hours ago, barrows said:

Keep the USB short.  At Sonore we use recommend Blue Jeans cable CAT 6A, which is not expensive.  But we are so busy testing things we do not get around to testing high end Ethernet cables.  Most tests I have seen have not usually tested the fancy Ethernet cables vs. a good commercial cable like BJC CAT 6A, but someday I will get around to it!

Okay, clear. Just a good Ethernet cable will do the job, I agree. BJC is a fine cable, but the Supra also and not expensive too. How about MQA? That will be a killer app with the UltraRendu! I have been reading it is coming soon, true?