Review and Measurements of Audio-gd NFB28.28 DAC and Headphone Amp

[VintageFlanker]

Maybe the beautiful insides biased lots of them

Oh yes, internals are beautiful. So much components for so poor measurements... That's a shame...

Here are my internal pictures of R2R-2 DAC and NFB-28.38:

R2R-2:

NFB-28.38:

 

[BurritoJustice]

I do believe that Kingwa and Audio-gd could make good measuring products if they really want to, at least from their internal build quality, but they just strictly adhere to an ancient and basic principle (no negative feedback) that makes them measure terrible independent of their build quality.

My question to @amirm is, is it possible to make a "perfect DAC" emulate the performance of a distortion heavy or otherwise inferior DAC? It seems theoretically possible to me, and as a poor DAC can never emulate a transparent one it could allow trying a distortion heavy design without dropping the cash. Or are the artifacts too variable to easily emulate?

 

[maxxevv]

Looks like there will be a major meltdown on some diehard fan forums soon ...

 

[Veri]

I do believe that Kingwa and Audio-gd could make good measuring products if they really want to, at least from their internal build quality, but they just strictly adhere to an ancient and basic principle (no negative feedback) that makes them measure terrible independent of their build quality.

I disagree. Soekris' R2R boards have NFB. No feed back but still miles and miles better than whatever audio-gd outputs
https://www.audiosciencereview.com/...rements-of-soekris-dac1421-multibit-dac.3956/

From soekris:
The line output buffer is a high performance zero feedback design built with discrete parts, the buffer also have a high power mode to drive any set of Headphones. The main power supplies are ultra low loise, low impedance and very fast, also built with discrete parts.

 

[derp1n]

I do believe that Kingwa and Audio-gd could make good measuring products if they really want to, at least from their internal build quality, but they just strictly adhere to an ancient and basic principle (no negative feedback) that makes them measure terrible independent of their build quality.

Basically the Chinese version of Schiit... pushing obsolete tech for mythical reasons.

 

[derp1n]

I disagree. Soekris' R2R boards have NFB. No feed back but still miles and miles better than whatever audio-gd outputs

https://www.audiosciencereview.com/...rements-of-soekris-dac1421-multibit-dac.3956/

Yeah but @soekris knows what he's doing... look at the board layout. It's as good as RME internals, from a one man project.

 

[BurritoJustice]

I disagree. Soekris' R2R boards have NFB. No feed back but still miles and miles better than whatever audio-gd outputs
https://www.audiosciencereview.com/...rements-of-soekris-dac1421-multibit-dac.3956/

From soekris:
The line output buffer is a high performance zero feedback design built with discrete parts, the buffer also have a high power mode to drive any set of Headphones. The main power supplies are ultra low loise, low impedance and very fast, also built with discrete parts.

I stand corrected, I had no idea that Soekris used non feedback designs.

I guess they just do a bad thing badly?

 

[andreasmaaan]

I disagree. Soekris' R2R boards have NFB. No feed back but still miles and miles better than whatever audio-gd outputs
https://www.audiosciencereview.com/...rements-of-soekris-dac1421-multibit-dac.3956/

From soekris:
The line output buffer is a high performance zero feedback design built with discrete parts, the buffer also have a high power mode to drive any set of Headphones. The main power supplies are ultra low loise, low impedance and very fast, also built with discrete parts.

Is there also no global or local feedback at any other stage in the Soekris DACs? Very interesting to see such an impressively low distortion figure if that is the case.

 

[Veri]

Is there also no global or local feedback at any other stage in the Soekris DACs? Very interesting to see such an impressively low distortion figure if that is the case.

From the measurements thread soekris himself said
The output buffer is a zero feedback design so it add a little 2nd and 3rd harmonics at high levels, lower the level a couple of dB and they don't dominate anymore.... Still, they're way below what you can hear.

As for "at any other stage" I'm not entirely sure, maybe the man himself can elaborate @soekris

 

[soekris]

From the measurements thread soekris himself said
The output buffer is a zero feedback design so it add a little 2nd and 3rd harmonics at high levels, lower the level a couple of dB and they don't dominate anymore.... Still, they're way below what you can hear.

As for "at any other stage" I'm not entirely sure, maybe the man himself can elaborate @soekris

Correct, our line of audiophile DACs, the dac1321, dac1421 and dac1541, all have output amplifiers with no negative feedback at all. It's all about the implementation, with careful design you can make some simple and very linear amplifiers.... Our R-2R DAC core is voltage out, we don't need any Current to Voltage converters and can therefore do with just a single stage output amplifier. As you can see from our inside pictures, it still takes a lot of small transistors, but a lot of them are just constant current sources to make sure the active parts operate perfect....

 

[Veri]

Very nice, @soekris thanks for taking the time to answer!

 

[BurritoJustice]

Correct, our line of audiophile DACs, the dac1321, dac1421 and dac1541, all have output amplifiers with no negative feedback at all. It's all about the implementation, with careful design you can make some simple and very linear amplifiers.... Our R-2R DAC core is voltage out, we don't need any Current to Voltage converters and can therefore do with just a single stage output amplifier. As you can see from our inside pictures, it still takes a lot of small transistors, but a lot of them are just constant current sources to make sure the active parts operate perfect....

If I ever were to buy a R2R dac, it would definitely be yours! Cheers

As was posed when the question was asked, is it likely that the Audio-gd units use a non-feedback design on areas that your DACs do not? I might be off base (I'm not familiar with the specifics of DAC design) but it is stated that your output stage is feedback-free, while audio-gd likes to say that there is no feedback in any stage of the design.

 

[soekris]

If I ever were to buy a R2R dac, it would definitely be yours! Cheers

As was posed when the question was asked, is it likely that the Audio-gd units use a non-feedback design on areas that your DACs do not? I might be off base (I'm not familiar with the specifics of DAC design) but it is stated that your output stage is feedback-free, while audio-gd likes to say that there is no feedback in any stage of the design.

Audio-GD and me are probably saying the same thing using different words.... It's the implementation they have problems with, they also use an ESS chip so they need additional stages for the current to voltage converter and filter stage, those additional stages also adds distortion....

 

[sbsj]

omg... been seriously considering the NFB28.38 to pair with the HD6XX. Some even say the NFBs sound "tube-ish". After reading lots of good reviews on NFB , with these measurements I now feel so lost and confused.

Coming from a non audiophile like me ( i am not an electrical engineer, I just love listening to music ), may i ask
- are measurements the ultimate guide on how good or bad a DAC / Amp sounds ? Would a dac / amp with the best measurements sound the best ?
- are "distortions" what makes the "tube sound" which a lot of people enjoy ? I recently tried the Felix Audio Echo tube amp. I have read alot of people say that the HD6xx / 650 sound best with tubes. I found this to be true with the Echo tube amp.

By the way Amir, have you measured any tube amps ? Do tube amps measure bad in general ?

As always, thank you Amir for your reviews !!!

 

[flipflop]

- are measurements the ultimate guide on how good or bad a DAC / Amp sounds ? Would a dac / amp with the best measurements sound the best ?

Yes and yes. Under blind listening conditions, people prefer high fidelity playback. This is true regardless of age, gender, cultural background, etc.
That said, it's not guaranteed that if an amp or DAC measures better than another one, it will sound better, because both could be audibly transparent.

- are "distortions" what makes the "tube sound" which a lot of people enjoy ?

That's an ongoing debate. I'm inclined to believe it's the high output impedance typically found in tube amps, which makes headphones with an impedance swing in the bass, such as the HD 650, sound muddier than they normally would be.

 

[Ron Texas]

Shittier than Schiit.

 

[andreasmaaan]

Coming from a non audiophile like me ( i am not an electrical engineer, I just love listening to music ), may i ask
- are measurements the ultimate guide on how good or bad a DAC / Amp sounds ? Would a dac / amp with the best measurements sound the best ?
- are "distortions" what makes the "tube sound" which a lot of people enjoy ? I recently tried the Felix Audio Echo tube amp. I have read alot of people say that the HD6xx / 650 sound best with tubes. I found this to be true with the Echo tube amp.

These are the big questions

IMHO measurements are a very good indicator of how something will sound, although most DACs measure well enough that there will be no audible differences between them (i.e. all distortion falls comfortable below known thresholds of audibility).

Distortion seems to be part of what makes the "tube sound", and there is some evidence from studies that many listeners prefer a just-audible amount of distortion over no distortion.

However, I doubt this alone accounts for the preference among many audiophiles for tubes, which I'd largely put down to psychology in most cases.

Here is an example of one study in which under properly controlled double blind conditions it was found that most listeners preferred a just audible degree of distortion over no audible distortion. And here is another.

Note however that neither of these studies were directly interested in distortion preferences. So I think while there's some evidence that many listeners prefer some audible distortion, it's fair to say that the jury is still out.

 

[sssn]

Looking at their website, you might think they're more obsessed about making pretty cirtcuitboards over well-measuring ones.
As NwAvGuy has said, electrical performance has nothing to do with components being arranged in neat, symmetrical rows and columns.

 

[Killingbeans]

- are measurements the ultimate guide on how good or bad a DAC / Amp sounds ? Would a dac / amp with the best measurements sound the best ?

I'm no expert, but here's my two cents:

Any DAC/Amp with distortion, noise and jitter below audibility will sound the same if they have the same frequency response and the same output impedance. Most of the time when a reviewer says a well designed Amp has a certain "color", it's down to impedance matching and/or a lumpy frequency response. The rest of time it's all make believe (psychoacoustics).

It's the kind of questions that poke a massive hornets nest

 

[Jkdjedi]

Devastating.

I have the 11.28 and knew i was listening to some distortion...just been in denial..until now!