Chord Qutest

[Superdad]

On 4/2/2018 at 6:53 AM, barrows said:

The Qutest is available at the price it is precisely because it eschews all of those features.

 

I try to eschew a lot of features myself, but they get stuck in my teeth.  

[Superdad]

2 hours ago, ecwl said:

I live in an apartment. I didn’t want to turn my living room into a hi-fi shop. 

 

?!!

[Superdad]

11 hours ago, ecwl said:

That said, having tried many USB DACs, I still find DAVE’s USB galvanic isolation to be amongst the best. But ultimately, if you want to get the very best USB performance out of Qutest, you still need to optimize your USB source.

 

Please remember that all DACs with digital isolator chips ("galvanic isolation") place them on the I2S lines AFTER the USB input PHY/processor.  Hence noise and leakage still affect the USB input stage.

Only current exception to this is the new $5,700 Auralic Vega G2--and some of PeterSt.'s Phasure NOS1a DACs. Those both use the same Silanna USB isolation chip--right at the input--as we use in the ISO REGEN.

[Superdad]

4 hours ago, Em2016 said:

The new iFi Pro iDSD? Or have they gone a different direction from their iGalvanic (which uses the same Silanna isolator)?

 

Based on photos of the boards that turn up in a Google search, it seems clear that the Pro iDSD has its digital isolator chips on the I2S/DSD lines at the output of their input board—just as is done with many other DACs/DDCs.  Nothing wrong with that.  Just means that the USB input stage still shares the same ground domain with the computer—unless one adds a GI device before the DAC.

[Superdad]

13 hours ago, Miska said:

Why would that matter as long as the clock is at the DAC side? USB interface just shovels data around and clock should run at the DAC side, on the other side of the isolation barrier. That way whatever happens at the USB side doesn't matter as long as there's no data corruption.

 

Well without opening up the usual can of worms, or getting too deep into why DAC USB input stages—even post-isolated ones— generate their own ground-plane noise and are affected by upstream variations in signal integrity, let me just pose this question:

If the digital isolators on the I2S/DSD lines in many DACs are truly effective, then why do users of those DACs still widely report hearing differences with various USB cables, as well as USB hub-based regenerators and galvanic isolators? 

[Superdad]

52 minutes ago, Middy said:

I work for Rolls Royce Aero so this is maybe my endgame for a good few years but i am glad i have it as its still very pleasurable and feel i got more out than the just ticket price.

Good luck gents and thank you

Dave

 

Hi Dave:

Rolls Royce Aerospace? Wow, that must be interesting work!

Your post sound a bit like a sign-off from the forum. If that's what you intend I just wanted to have the chance to say goodbye and let you know that I have enjoyed your many posts these past 4 years or so.  Wishing you good heath and great sound!

Warmly,

--Alex C.

[Superdad]

1 hour ago, jos said:

Right now, I am using the Chord Qutest with the new iFi iPower X, and before with the old one. To be honest: I can't hear a difference with my old ears.

 

Do you have a modest linear PS to try with your Qutest?  Lots of leakage (common-mode AC traveling over DC connections) from those iFi iPower SMPS units. (Same with all SMPS.)

[Superdad]

21 minutes ago, Miska said:

Not with the medical grade ones I use...

 

Those do still have 'Y' capacitors and have a form of leakage. See:

 

[Superdad]

16 hours ago, Miska said:

Unless you are using wrong type of Ethernet cable, it doesn't have any ground connection. Only transformer isolated differential signals.

 @ecwl was incorrect to refer to “ground loop leakage.”  The leakage currents blocked by the EtherREGEN are common-mode differential AC, which sail right through the port transformers.

[Superdad]

3 hours ago, The Computer Audiophile said:

Ayre uses optical isolation inside the QB-9

As with virtually any DAC with digital "galvanic" isolators (of whatever stripe), those are on the I2S lines--AFTER the USB input stage.  They do not isolate the USB input stage itself from what comes before. Just sayin'... 

[Superdad]

8 hours ago, Womaz said:

Ok I am considering both of these options , the powerbank seems the easiest as I think I understand how it would work.

Forgive my lack of knowledge as this is a sort of first attempt at tinkering.

Keep in mind that a typical “power bank” battery is comprised of several cells of lower voltage in series and that their output is derived from DC-DC switching regulators with little regard to noise or output impedance performance.  So while such units will provide a completely “floated” isolated power source, the quality of their output will not equal that of a well done LPS. 

Some folks using power banks follow them with an LT3045 regulator module, but since all LDOs need some drop to regulate the voltage from the battery feeding the regulator stage would need to be at least 5.7V.

[Superdad]

Wow! Guess it’s time to dig out from the attic my old bowling ball. Now if only you can give a recommendation as to where in my hi-if to repurpose the dorky-looking bowling shoes.