Topping Centaurus R2R DAC Review

[Mnyb]

R2R NOS DACs were never on my radar before, they were just a curiosity until the Centaurus came out. I started reading a few reviews and measurements and got curious.
The latest fave rave seems to be the Holo Audio May, which throws digital audio theory out with the bathwater in NOS mode, but many love it.

I'm struggling to understand what they're trying to do, and three things are often wrapped together, which doesn't seem right to me. Am I misunderstanding?

1. R2R DACs use a switched ladder network of filters to implement the conversion, which is an old, simple and expensive implementation.
2. Most DACs use digital filters to perform over-sampling, but NOS DACs don't do this, they convert at the native rate. This avoids pre-ringing and post-ringing.
3. NOS DACs seem to necessarily avoid using the low pass reconstruction filter, or at least one that only filters 44.1kHz

These three things are often considered collectively, but I'm sure they're separate.

1. R2R DACs are just a different architecture for performing the DA conversion. It's not very linear, and maybe people are just nostalgic? I don't care.
2. Digital filters have different frequency and time domain responses, depending on whether they're linear or minimum phase, fast or slow. The ringing is usually at 22kHz and shouldn't matter, but some people have preferences for one or another. I think NOS DACs don't use digital filters (or they're just switchable) and they don't have ringing, just lots of HF distortion instead.
3. NOS DACs don't use reconstruction filters, you just get an un-smoothed analogue output and live with that, hoping that the steps are inaudible.

John Atkinson sometimes measures the time domain effect of the different filters. Here are the Holo May in OS and NOS modes, and the MBL N31 with slow filter respectively:
View attachment 413929View attachment 413927View attachment 413928
The NOS time domain response to an impulse is just that - an impulse, without any pre- or post-ringing from the DAC (though the frequency domain response is compromised).
My point is that the NOS impulse response is really very similar to the MBL slow filter response above - not the same but very similar.
Is that where the benefit in a NOS DAC comes from? But can't you achieve much the same thing with a conventional DAC and a slow filter instead?

These impulse curves get misinterpreted all the time .

These are impulses with special test signals . The ringing does not happen with a music signal that are properly sampled and bandwidth limited .
They are realy for the engineers to study how well the filter works , perfectly symmetrical ringing is the expected results for the usual sample theorem compliant filters for example and is not a bad thing.

 

[Roland68]

@Roland68 wrote:
The D90 III Discrete is an r2r DAC and is therefore primarily intended for a different group of buyers, such as the Gustard A26 and R26. So it is an additional option in the same price range.
The first D90 was replaced by the D90SE because AKM DAC chips were not available, the D90LE was just the additional version without MQA (at the customer's request).
In the end, Topping only released a successor to the D90SE after 3 years.

The D90 III Discrete is an r2r DAC and is therefore primarily intended for a different group of buyers, such as the Gustard A26 and R26. So it is an additional option in the same price range.
The first D90 was replaced by the D90SE because AKM DAC chips were not available, the D90LE was just the additional version without MQA (at the customer's request).
In the end, Topping only released a successor to the D90SE after 3 years.

No, my mistake, I was wrong.
@yys310 corrected me a few posts later and wrote that it is not an R2R DAC but a DAC with a 1-bit DSM module.
I am no longer sure whether I got this information from a Topping employee at the trade fair stand or whether I had confused it with another DAC.

The rest should be correct though.

 

[NTTY]

R2R NOS DACs were never on my radar before, they were just a curiosity until the Centaurus came out. I started reading a few reviews and measurements and got curious.
The latest fave rave seems to be the Holo Audio May, which throws digital audio theory out with the bathwater in NOS mode, but many love it.

I'm struggling to understand what they're trying to do, and three things are often wrapped together, which doesn't seem right to me. Am I misunderstanding?

1. R2R DACs use a switched ladder network of filters to implement the conversion, which is an old, simple and expensive implementation.
2. Most DACs use digital filters to perform over-sampling, but NOS DACs don't do this, they convert at the native rate. This avoids pre-ringing and post-ringing.
3. NOS DACs seem to necessarily avoid using the low pass reconstruction filter, or at least one that only filters 44.1kHz

These three things are often considered collectively, but I'm sure they're separate.

1. R2R DACs are just a different architecture for performing the DA conversion. It's not very linear, and maybe people are just nostalgic? I don't care.
2. Digital filters have different frequency and time domain responses, depending on whether they're linear or minimum phase, fast or slow. The ringing is usually at 22kHz and shouldn't matter, but some people have preferences for one or another. I think NOS DACs don't use digital filters (or they're just switchable) and they don't have ringing, just lots of HF distortion instead.
3. NOS DACs don't use reconstruction filters, you just get an un-smoothed analogue output and live with that, hoping that the steps are inaudible.

John Atkinson sometimes measures the time domain effect of the different filters. Here are the Holo May in OS and NOS modes, and the MBL N31 with slow filter respectively:
View attachment 413929View attachment 413927View attachment 413928
The NOS time domain response to an impulse is just that - an impulse, without any pre- or post-ringing from the DAC (though the frequency domain response is compromised).
My point is that the NOS impulse response is really very similar to the MBL slow filter response above - not the same but very similar.
Is that where the benefit in a NOS DAC comes from? But can't you achieve much the same thing with a conventional DAC and a slow filter instead?

Impulse of a NOS relates to zero hold function of a DAC. It generates tons of aliases out of band, which also come back disrupt in audio band by IMD.
If someone is into trying to destroy their tweeter, it's a good option.
Of course, this is not to mention the -3.92dB roll off at 20kHz of a NOS DAC, because of the sin(x)/x envelope related, again, to zero function of the DAC.

There are many DACs with a "pseudo NOS" filter, that is a super slow filter mimicking NOS, again for those into unwanted useless noise at high frequencies.

The representations of John above are one way to look at the characteristics of a filter (you can achieve the same with a square or looking at white noise in wide band). Avoid the one in the middle (and probably right too, it seems super slow filter).

All of this is unrelated to R2R conversion, it applies to 1bit as well.

 

[totti1965]

No, my mistake, I was wrong.
@yys310 corrected me a few posts later and wrote that it is not an R2R DAC but a DAC with a 1-bit DSM module.
I am no longer sure whether I got this information from a Topping employee at the trade fair stand or whether I had confused it with another DAC.

The rest should be correct though.

Ah, I thought: If in the converting process no chip is included, then it is automatically R2R. So Topping has 3 Different DACs with exact same $ 999 price and 3 different techniques: D90 III / D90 III Discrete / Centaurus.
To complicated for me: I will go with the Holo Audio Cyan II.

 

[welwynnick]

These impulse curves get misinterpreted all the time .
These are impulses with special test signals.

Just like a 1kHz sine is a special test signal, but opposite case. An impulse is a vertical line in the time domain and a sine is a vertical line in the frequency domain.

My point was impulse response might be the advantage that NOS fans were clinging to, considering that all the other measurements are worse.

 

[Roland68]

Ah, I thought: If in the converting process no chip is included, then it is automatically R2R. So Topping has 3 Different DACs with exact same $ 999 price and 3 different techniques: D90 III / D90 III Discrete / Centaurus.
To complicated for me: I will go with the Holo Audio Cyan II.

Take a closer look at the Topping DX9, an exceptional device in many areas.

 

[oleg87]

Serious question: how do we think that R2R DACs got their audiophile status?

This is a question for students of social psychology, suggestibility, and marketing.

 

[Mikig]

What makes it justified against a cheaper and unflawed DS DAC?


I'm attracted by real engineering merits. For instance, by products that are built to last and have a long lifecycle and adequate aftersales support processes. By manufacturers who make an effort to provide comprehensive documentation. By products that have really useful features instead of gimmicks and that are not only not subject to planned obsolescence, but kept up to date long after the initial release. This is what makes "fascinating engineering" in my book.


Yes, for them these are indeed giant steps.


From people who only recently learned to read IC implementation notes and discovered the existence of the AP555 analyzer? From those who are struggling to produce an amplifier that does not kill your headphones? Good joke.

this Dac is in the excellent part of the measured performances so it does not seem defective to me ... regardless of its price it is a device with excellent performances. If it bothers you that it is R2R with excellent performances, it is a subjective thought of yours, objectively here there can be no criticism. ...
what you say in the rest of the post is sadly common to EU, USA, GB products and brands ... I'll give you a list of how many problems I've had in recent years with German cars, washing machines, smartphones, boilers, computers, which are produced behind the house??
if you want I'll also tell you that no one has ever given me spare parts or even bothered to resolve frankly embarrassing situations ...
it seems to me anyway that a good part of the noble hi-fi brands essentially sell technologies and products made and designed in China in luxurious boxes and with plenty of "communication" and marketing ...
the technology comes from there ...

 

[dtaylo1066]

Unless I listened and my subjective mind took over and told me I was being blown away by the magical sound, I see no reason to pay the price for this excellent performing DAC. I would be interested to see how the new, inexpensive FIIO R2R offering measures.

 

[unpluggged]

this Dac is in the excellent part of the measured performances so it does not seem defective to me ...

The IMD and the FR graphs alone are sufficient to look elsewhere for "engineering excellence".

what you say in the rest of the post is sadly common to EU, USA, GB products and brands ... I'll give you a list of how many problems I've had in recent years with German cars, washing machines, smartphones, boilers, computers, which are produced behind the house??

How cars, washing machines and other consumer commodities are relevant here? I have experience of dealing with vendors who stand behind their products and with "vendors" who don't care. And the latter are mainly those guys who try to push gimmicks and release a new half-baked product each week.

if you want I'll also tell you that no one has ever given me spare parts or even bothered to resolve frankly embarrassing situations ...

So you then insist on continuing giving your money to such manufacturers, just to other ones?

it seems to me anyway that a good part of the noble hi-fi brands essentially sell technologies and products made and designed in China in luxurious boxes and with plenty of "communication" and marketing ...

Then avoid such manufacturers.

the technology comes from there ...

One should not confuse technology with producing facilities.

 

[Kaameelis]

But can't you achieve much the same thing with a conventional DAC and a slow filter instead?

No, any filter have influences on impulse response, regardless is filter on digital or on analog side, all filters will add pre or post ringing, depending of filter type.

 

[Martin]

I think I'll keep my E70.

Martin

 

[Sokel]

On a different but somewhat related topic (if not, I hope our mod will delete it for me), I wonder if there exist a device that could easy add a variety of harmonics to get the effects that antcollinet described in post#38? NP, iirc had a sort of DIY, prototype one but I really want to buy one that is a finished off the shelf product that can be readily wired into some point of my preamp/dac/dsp signal chain, and the harmonics addition should be reasonably variable and the adjustments visible on its own display or at least a PC. If such a device doe not exist, I hope it will, in the near future.

It seems to me frequency response and THD, and may be its frequency dependence too, are probably the main reason for audibly and obviously measurably different sound quality, as other metrics such as linearity, FR, DF, IMD, DR/SNR, multitone inputs, (usually very low if THD is very low), cross talk, and all the stuff that Amir has been measuring tend to be transparent enough for most devices that are on his recommended list.

I think this is sort of still on topic because there must be members who are interested in why R2R DACs sound different, assuming some do sound different in blind listening tests.

You can play around easily with the new DAC's "sound color" options and get from 120dB SINAD to 40dB SINAD with a click,SMSL,Topping,etc has this mode.

 

[Sir Sanders Zingmore]

All tests are in default 4 volt mode instead of 5 volts (and "PRE" mode).

Given that most buyers of R2R DACs are “purists” who probably listen in NOS mode, it be would be great to see the full suite of measurement in that mode.

 

[Sokel]

As a side note,disregarding Centaurus,what differences one expects comparing a good 118dB SINAD Holo May R2R with a 120dB SINAD whatever?
I could design a scenario where playing levels along with recorded levels can bring some DAC's flaws to audible regions with special signals but that's it.
Good luck discriminating them with music.

 

[Soria Moria]

Serious question: how do we think that R2R DACs got their audiophile status?

The old audiophile adage of "It's old, outdated, clunky and expensive, therefore it must be good".

 

[NTTY]

As a side note,disregarding Centaurus,what differences one expects comparing a good 118dB SINAD Holo May R2R with a 120dB SINAD whatever?

None

I could design a scenario where playing levels along with recorded levels can bring some DAC's flaws to audible regions with special signals but that's it.
Good luck discriminating them with music.

Make it 60dB worse and I can participate, else no way I can discriminate anything

 

[Mikig]

The IMD and the FR graphs alone are sufficient to look elsewhere for "engineering excellence".


How cars, washing machines and other consumer commodities are relevant here? I have experience of dealing with vendors who stand behind their products and with "vendors" who don't care. And the latter are mainly those guys who try to push gimmicks and release a new half-baked product each week.


So you then insist on continuing giving your money to such manufacturers, just to other ones?


Then avoid such manufacturers.


One should not confuse technology with producing facilities.

given the past experience of R2R at discrete, I would say that the test indicates that this Dac is competent in all respects with some excellent points.

"The objective performance of Centaurus seems to be the best that can be done with R2R technology."

I think that regardless of personal tastes it is a good goal for Topping and an excellent point of arrival for this technology that, if performed with care, can have its say. If you want, instead of cars, washing machines and boilers I can tell you that I was lucky enough to lend a hand to a friend who had a hi-fi shop for years. Even "noble" brands have problems, and don't believe that distributors jump for joy when you call them to tell them that the device or speaker in question has problems ... on the contrary!!

I buy what I happen to buy, what I need, but above all what I like. Regardless of everything: I have no preconceptions or prejudices. Normally I happen to buy used devices, if you want let's call them vintage. I keep my Hi-fi collection alive, so when I find something that interests me…..I take it!!

 

[NTTY]

given the past experience of R2R at discrete, I would say that the test indicates that this Dac is competent in all respects with some excellent points.

For what I can see, it’s crazy good for discrete R2R. I’d have never thought it would be that good.

"The objective performance of Centaurus seems to be the best that can be done with R2R technology."

Obviously.

I think that regardless of personal tastes it is a good goal for Topping and an excellent point of arrival for this technology that, if performed with care, can have its say.

I concur with that.

I buy what I happen to buy, what I need, but above all what I like. Regardless of everything: I have no preconceptions or prejudices. Normally I happen to buy used devices, if you want let's call them vintage. I keep my Hi-fi collection alive, so when I find something that interests me…..I take it!!

Welcome to the club

 

[Mikig]

For what I can see, it’s crazy good for discrete R2R. I’d have never thought it would be that good.

Obviously.

I concur with that.

Welcome to the club

I have my own little shop!!
I am currently using in my second system, the one for games, a Dac with double PCM63, I found it, bought it for a few euros, brought it home, cleaned it, and restored it: I restored a Rotel integrated, and the result makes me happy. I took back a tube power amp, cleaned it well too, made two changes, changed all the tubes, it is a little gem…..

I have a list of devices that I would like to have……with time!!!!