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Differences in sound: DAC vs. DAC + Pre-amplifier


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On 6/6/2020 at 9:41 PM, barrows said:

The above is not possible, the clock frequencies required for Ethernet transmission and audio data are different.

 

While I agree that a direct ethernet connected DAC is a desirable thing, in practice it is very difficult to implement a good Ethernet interface inside a DAC.  By no means am I suggesting it is impossible to do so, but doing so does require paying attention to a lot of details.  Decoding Ethernet data to digital audio samples requires quite a bit of processor power, quite a bit more than, for example, USB audio processing to digital audio data.  And even USB interfaces inside DACs benefit a lot from careful implementation and isolation.  For example, a typical USB interface requires around only 200 mA of power at around 5 VDC, whereas even a less capable (sample rate limited) Ethernet interface requires at a minimum 500 mA of power at 5 VDC, and a better Ethernet interface (like Sonore's optical) requires well over 1 A at 7 VDC to work with higher sample rates.  This power requirement transfers fairly directly into processor noise, inside the DAC chassis.

Currently, most DACs (not all) with inbuilt Ethernet interfaces are both sample rate limited, and not adequately isolated from the DAC circuitry.  Mostly this is because most DAC companies are quickly adding Ethernet interfaces using relatively affordable, off the shelf modules, of limited performance.  One exception is Lumin, and another is Linn, although while the Linn Klimax DS provides superb performance, it is still sample rate limited.

 

The way to do it right:

 

1. Design your own Ethernet interface (preferably with optical input for noise isolation), capable of all sample rates to PCM 768 and DSD 512 (or higher).  And be sure to use high end design approaches all around, many low noise regulated supplies, high precision ultra low phase noise oscillator, etc, etc.  Not an affordable off the shelf module.  Designing such a module requires an engineer highly skilled in high speed circuit engineering, preferably someone with extensive computer mother board design expertise, typical engineers at audio companies do not have the required expertise for this, so the dAC manufacturer will likely have to sub-contract a suitable engineer for the project.

 

2. Make sure the digital audio output (I2S) from he Ethernet interface is fully galvanically isolated from the rest of the DAC.  Note that to provide full galvanic isolation it is also necessary to supply power to the Ethernet interface from a dedicated supply, preferably from a separate dedicated transformer.

 

3.  Make sure the Ethernet interface is physically shielded in a separate sub enclosure to reduce the amount of airborne RF pollution on the inside of the DAC chassis which can couple into the analog outputs.  Note that both Lumin X-1, and Linn Klimax DS do appear to address this need, as does the Mola Mola Tambaqui.

 

I would expect to pay around a $2K USD premium for a really good Ethernet interface inside a DAC, all other things being equal. This can come at some savings if the DAC maker is willing to forgo other inputs altogether, which would be my preference for best sound quality: simple has its advantages.  An Ethernet only input might be able to come with a $1.5K USD premium over the same model DAC with only typical inputs.

 

 

 

How do you ensure "perfect galvanic isolation"? With what technology?

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1 hour ago, barrows said:

 

A lot of stuff there I put in quotes, usually when I put "perfect" anything regarding electronics i put it in quotes.  Perfect in this sense is a concept, which may never be achieved, or it might be in some instances,

 

In any case, different engineers have different preferences when it comes to which isolation technologies to use.  These are used to isolate USB interfaces from the rest of the DAC as well.  Some are GMR based isolation chips (these are magnetically based on a chip), some choose optical isolation chips, some use capacitive isolation chips, and some might choose to use larger magnetics (non chip based transformers).  I am not a high speed circuit designer, and have no opinion on which approach might be best in any given situation.  But I have plenty of experience comparing isolated USB interfaces to non-isolated USB interfaces, and isolated is superior, and does result in a large degree of noise reduction from the USB interface to the DAC conversion and analog stages, nothing is perfect though.  But, the point being that if one wants an Ethernet interface inside a DAC (and I am one who does), best practice would be to isolate it by using one's favorite/best isolation approaches and maintain that isolation by powering it from a dedicated power supply, including a dedicated transformer.  Additionally, i would prefer an Ethernet interface to be physically shielded from the DAC circuitry in its own sub enclosure to avoid airborne RF interference.  Take a look at internal photos of the Lumin X-1 DAC, for example, it follows these design implementations

 

None of these isolation measures is going to be perfect though, nothing is (consider that there may be noise crosstalk at the AC input itself, for example), but such measures when done well have proven to improve DAC performance to levels where further efforts in this direction are probably not going to result in any actual audible change.

 

So tell me if I understand correctly:

 

- you are not specialized in this field

- you acknowledge that you are basing your claim on comparing what could very well be "imperfect" solutions

 

Yet you go around claiming in all threads the superiority of a given architecture? 

 

"such measures when done well have proven to improve DAC performance to levels where further efforts in this direction are probably not going to result in any actual audible change." 

 

Hmmm

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1 minute ago, barrows said:

Isolation of USB and Ethernet receiver circuitry is a well understood and fairly mature technology, and there is not much debate about how to do it properly, it is accepted tech

 

There actually is debate about its efficacy! 

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12 minutes ago, barrows said:

I am really unsure as to what your motivation is here?  It is generally accepted that it is proper engineering to isolate noisy digital audio interfaces which include high speed processing chips (USB or ethernet qualify for this) and most well implemented USB DACs, and some Ethernet DACs do exactly that: I am not exactly advocating for anything controversial here.  Is there some other approach which you would advocate for or something, or are you just looking to create Internet based tensions?

 

Why are you questioning my motivation ? 

 

I am not challenging the fact that isolating noisy digital audio is "proper engineering" - please don't misquote me. I am challenging the fact that you are "selling" in most of your posts a given "architecture" based on solutions which are unproven and debated.

 

The fact that you have worked 20 years in audio changes nothing to that. Sorry :)

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17 minutes ago, barrows said:

I questioned your motivation because I had no idea why you would challenge what is fairly basic, accepted, best practice for implementing digital receivers without citing any other approaches of note.

 

I did not misquote you, any quotes i posted were taken directly from your posts?

 

OK, so experience counts for nothing with you, I must say i do not really get that: say your getting a heart transplant, woudl rather have a surgeon who has done the procedure before, or a first timer?

 

I will take a look at the thread you reference.

 

And by the way, i am not "selling" anything here.  I currently have no affiliation with any company which produces any commercial DAC for sale.  My opinions are my own, as the result of my experiences and the experiences of the engineers I have discussed the subject with over the years.

 

I would disagree that isolating USB (as well as ethernet) interfaces is an "unproven" approach.  It is actually well proven by many, many companies making DACs.  In fact, most of the better DACs available use this approach, and if one measures carefully, for things like USB packet noise, for just a single example, one can show in measurements that well engineered isolation reduces noise in a DAC's output.

 

 

Once again. I am not challenging the NEED to isolate, but how it is done and what results it achieves. 

 

If i were to get a heart transplant I would prefer going with a surgeon who has a proven track record. 

 

I am not saying experience NEVER counts (please stop putting words in my mouth), I am just trying to understand how you substantiate your claims, since every other thread on digital audio in this forum seems to be a platform for you to express them. Digging a little deeper is not a crime. 

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8 minutes ago, barrows said:

 

@hopkins, are you associated with EC designs?  If so, you probably should reference such in your signature.

 

I took a quick look at their website, and I find it kind of confusing that at first they criticize USB, but then their interface is just a D-D converter form USB to toslink?  Weird way to go if you think USB is problematic in the first place.

 

I have zero interest in anything that has anything to do with Toslink, there are MUCH better optical interfaces available, and even if their interface has incredibly good output, it will be compromised by the cheap Toslink receiver on any DAC (I assume they make something better on their own DAC).

 

Also, interfaces which are sample rate limited are of no interest to me.  I prefer higher rate DSD so all this and R2R PCM specific DACs hold no interest for me as well.  Although if one must use PCM, a really good R2R approach can sound nice.

 

Measurements do not show most of the problems they claim there can be with USB when good isolation is implemented, they just seem to claim such and offer no evidence.  I would expect their optical isolation of USB to work well if they implemented it well, such an approach could be used inside any DAC of course.  And it could be applied to an Ethernet interface as well: i look forward to seeing actual measurements showing that this approach improves on already accepted approaches in wide use.

I do believe ground loops can be a problem with USB: this depends the source used: I prefer a USB source which is floating for the USB output for this very reason: some DACs will be sensitive to this, some will not-certainly with DACs which have non-isolated USB interfaces ground loops can be an issue.  But if the USB source is floating, there is no problem.

 

No, I am not associated in any way with ECDesigns. I am a consultant, like you, but in IT - nothing to do with audio.

From the summary you give, I suggest you spend a little more time reading the link I gave you.

 

P.S. If you are not affiliated with any audio companies, why does your profile state "Product Development Consultant with SONORE" ?

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23 minutes ago, barrows said:

Yeah, i read the entire post.  Lots of words, but zero measurements.  Like i said, it might be interesting to use their approach to isolate the Ethernet or USB input in a DAC, and then measure compared to conventional approaches using isolation chips.  I would like to see that comparison.  So far, the measurements I have seen of conventional isolation approaches do not exhibit the large amounts of high frequency noise and poor ground isolation which EC Designs claims.  But if their approach is really that superior in terms of isolation, I am all for it and getting it in a package which can be reasonably implemented to isolate the Ethernet or USB input inside a DAC.  Optocouplers are already used for this by some companies of course, but increasing the distance of the input side to the output side should reduce capacitive coupling, whether this actually results in a meaningful difference needs to be proven.  

 

I assume there is a good reason why their optical isolation is placed at the DAC's input, and that the USB processing is done before the optical signal is send to the DAC. You can enquire about that with them, I cannot comment on your speculations.

 

As for "sample limited" versus DSD, perhaps you should keep an open mind about that as well, given that you have probably only heard digital with "less than perfect" isolation (to quote you). 

 

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Actually I did listen briefly to the Mola Mola Tambaqi, which does internal conversion to DSD, in a good setup at a reviewer's house. While it is a good DAC, in comparison to another high end DAC that was being used that day I would mot say it was a night and day difference. There are so many aspects in which a DAC can go wrong or do things right... 

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35 minutes ago, barrows said:

Exactly, and by using Ethernet you keep noise from the server coming in.  Specifically, best practice is to use optical fiber Ethernet.  No matter what extremes one goes to trying to make a server as silent as possible, that server will never be as silent as well designed Renderer.  I suggest, that the better approach, is not bother about making the server silent.  Put it in another part of the home, and do not let its electrical noise to get to the audio system, by sending the music to the audio system over Ethernet (which is isolated by transformers), or even better, with optical fiber Ethernet (which does not pick up and carry electrical noise at all).

The the only noise which gets to the audio system is that generated locally, in the audio system.

 

There is another big advantage to Networked Audio as well:  You can do as much processing in the server as you may want, run room correction, for example, or much more sophisticated oversampling programs like HQPlayer (which can be a big sonic advantage, especially HQPlayer oversampling and a simple DAC which does no additional processing onboard, reducing noise in the DAC even further).  All this processing in the server makes a lot of noise, but by isolating the server away form the audio system, connected by only an optical fiber cable, the noise never gets to the audio system.  

 

Using optical fiber and thinking it actually provides isolation is complete nonsense because you are still putting an ethernet chip inside the DAC. 

 

There are no measurements to back up the fact that this is a superior solution. 

 

 

 

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Once again

 

"such measures when done well have proven to improve DAC performance to levels where further efforts in this direction are probably not going to result in any actual audible change"

 

Peace. Will no longer reply here. Have a great day! 

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Keep in mind that you have several layers  to the equation:

 

- the computer that converts the music files to a USB or Ethernet data stream

- the conversion of that data stream to a digital audio signal

- the DAC itself

 

In the setup that Barrows recommends, the data stream is handled in a two step process, with heavy lifting on one computer, and then passed on to a second through an optical fiber network. The "renderer" is then connected to USB directly to the DAC. There is nothing really new here. 

 

Since USB isolation is less than perfect, you are still getting noise into the DAC. Barrows believes that you can get that noise down to levels that are not audible...That's purely speculation.

 

There is no theory to back this up, no measurements either and no "listening" can prove it either because by definition you are comparing several setups which are all flawed. 

 

In a system where the DAC is "exposed" through USB input its a very risky proposition to believe that you can achieve any breakthrough  by tinkering with the sources. 

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