Review and Measurements of Audio-gd NFB-27.38 DAC and Headphone Amplifier

[Krunok]

And who is it that once was responsible for audio in Windows?????

LOOL

 

[trl]

These words, at least in my eyes, are perfectly explaining the truth behind subjective listening tests vs objective measurements: not only that the difference, that is so obviously shown on measurement equipment, can easily be overlooked during listening tests, but can also be found to be more appealing to some people.

More harmonics sometimes mean better sounding, same applies if a bit of distortions occur. That means "better sounding to my ears" is on top of your measurements.

 

[Krunok]

More harmonics sometimes mean better sounding, same applies if a bit of distortions occur. That means "better sounding to my ears" is on top of your measurements.

I believe that is true as most of my friends prefer the sound of tube amp to that of SS amp. But still, in that case we're not talking "High Fidelity" any more..

 

[trl]

[...] in that case we're not talking "High Fidelity" any more..

So true!

 

[Veri]

I believe that is true as most of my friends prefer the sound of tube amp to that of SS amp. But still, in that case we're not talking "High Fidelity" any more..

You telling me feeding the clean signal of a super low distorting, super linear great performing DAC,

into a much dirtier 0.2-0.5% THD distorting tube amp full of second harmonic distortions is not high fidelity? (I'm half joking half serious here lol, I guess the benefit of the clean DAC signal is totally lost in this case. Or... not?)

 

[Krunok]

You telling me feeding the clean signal of a super low distorting, super linear signal of a great performing DAC,

into a much dirtier 0.2-0.5% THD distorting tube amp full of second harmonic distortions is not high fidelity? (I'm half joking half serious here lol, I guess the benefit of the clean DAC signal is totally lost in this case. Or... not?)

It's "tube fidelity"!

No, benefit of the clean DAC is still there allowing you to fully enjoy that sweet harmonic distortion that tubes produce. Oh yes, and that glow as well, especially if you're in good company, holding a glass of wine.. I believe you've got the picture.

 

[Frank Dernie]

I think some of Menno's toroids will do pretty well in that respect. And of course, Berning's "virtual" transformers work as well as claimed. See figure 2 here, for example:
https://www.stereophile.com/content/linear-tube-audio-zotl40-mkii-power-amplifier-measurements

I'll show some similar data in my upcoming review of the Linear Tube Audio Ultralinear.

The output impedance is still too high though. My guess is that anybody noticing a difference in sound between one of these and a modern conventional SS amp is as likely to be hearing the effect on the frequency response of their speakers of their high output impedance as any distortion products.
Several expensive SS amps have output impedances which will make them sound different on audition. For those for whom very expensive implies better any difference may well be perceived as an improvement.

 

[Krunok]

The output impedance is still too high though. My guess is that anybody noticing a difference in sound between one of these and a modern conventional SS amp is as likely to be hearing the effect on the frequency response of their speakers of their high output impedance as any distortion products.
Several expensive SS amps have output impedances which will make them sound different on audition. For those for whom very expensive implies better any difference may well be perceived as an improvement.

Heh.. "with 32Wpc (12dBW) available at 1% THD+N". Modern SS amplifiers would have less than 0.01% at this power. High end speakers will have <0.1% (above 200Hz). From that perspective I believe it is obvious which distortion will be mostly heard.

 

[rebbiputzmaker]

Also, the drivers are sent from a third-party, using .rar

RAR has been used since the 90s and has advantags over zip. Winrar is available and is not malware. I am supprised someone with your computer expertese has not used this.

https://www.rarlab.com/download.htm

 

[Frank Dernie]

Heh.. "with 32Wpc (12dBW) available at 1% THD+N". Modern SS amplifiers would have less than 0.01% at this power. High end speakers will have <0.1% (above 200Hz). From that perspective I believe it is obvious which distortion will be mostly heard.

Are you aware of the frequency response errors one gets from one's speakers when driven by a high output impedance amplifier?
It obviously depends on the impedance characteristics of the speakers, and will have the biggest effect around the crossover frequencies.
It is not only the distortion which makes these valve amps sound different, the alteration of the frequency response is well above audible limits (whereas it is often debated whether 1% is audible with music rather than pure tones).

Also whilst there are speakers with <0.1% distortion in the mid band they are not common and some of them are not "high end", I know of a car speaker used on a mass produced car which is this good over a broad range and costs less than £1 each.

 

[Krunok]

Are you aware of the frequency response errors one gets from one's speakers when driven by a high output impedance amplifier?

I don't think anybody mesure's that. And why do it - it is amplifier's task to drive the speakers properly, not vice versa. Anyway, if that will cause non linear response it would anyhow manifest as harmonic or IM distortion.

It obviously depends on the impedance characteristics of the speakers, and will have the biggest effect around the crossover frequencies.

Low impedance points of the speakers doesn't correlate with crossover frequencies.

It is not only the distortion which makes these valve amps sound different, the alteration of the frequency response is well above audible limits (whereas it is often debated whether 1% is audible with music rather than pure tones).

Oh, and what else beside harmonic and IM distortion makes them sound different? Orange glow?

Also whilst there are speakers with <0.1% distortion in the mid band they are not common and some of them are not "high end", I know of a car speaker used on a mass produced car which is this good over a broad range and costs less than £1 each.

Very interesting! Can you please post a link to the measurements proving that?

 

[Frank Dernie]

I don't think anybody mesure's that. And why do it - it is amplifier's task to drive the speakers properly, not vice versa. Anyway, if that will cause non linear response it would anyhow manifest as harmonic or IM distortion.



Low impedance points of the speakers doesn't correlate with crossover frequencies.



Oh, and what else beside harmonic and IM distortion makes them sound different? Orange glow?



Very interesting! Can you please post a link to the measurements proving that?

Stereophile ALWAYS measure the effect of the amplifiers output impedance on the FR of a simulated loudspeaker load in every amp test they have done for decades. Didn't you look at the link to the ZOTL amp test I was replying to before making your comments?
It is the impedance variations which cause the FR inaccuracies, it is not the fact that it may be low.
There are some very knowledgeable people posting on this forum. You are not one of them.
The car speaker is a proprietary design done by a friend of mine and fitted as standard to a large range of a certain manufacturer's cars, It's characteristics are commercially confidential. If you feel the need to disbelieve it, feel free.

 

[amirm]

RAR has been used since the 90s and has advantags over zip.

Those "advantages" (better compression) in the 90s don't mean jack today when we are talking about a small driver package with fast Internet everyone has.

am supprised someone with your computer expertese has not used this.

Thanks for the jab. Let me tell you what that computer expertise tells me: zip decompression is built into Windows. Forcing someone to go hunt around for another decompressor to download and install prior to getting the driver expanded and before you can get the DAC working is bad, bad, practice. There is a thing called "usability" in computer software development. And that is what I am commenting on, not any competition between rar and zip.

 

[Veri]

Wait until amir bumps into a driver that is supplied into a .7z file

I do agree though, when I do a fresh OS install and end up with some .rar that I cannot open without further software installation is not really the way to go to distribute something.

 

[Krunok]

There are some very knowledgeable people posting on this forum. You are not one of them.

I kindly ask Moderator to teach @Frank Dernie how to communicate in a civilized manner as obviously his parents failed to do so.

 

[Thomas savage]

Those "advantages" (better compression) in the 90s don't mean jack today when we are talking about a small driver package with fast Internet everyone has.


Thanks for the jab. Let me tell you what that computer expertise tells me: zip decompression is built into Windows. Forcing someone to go hunt around for another decompressor to download and install prior to getting the driver expanded and before you can get the DAC working is bad, bad, practice. There is a thing called "usability" in computer software development. And that is what I am commenting on, not any competition between rar and zip.

Amir slips the jab , great lateral movement from the fleet footed Iranian opens up the angle for a body head combo ..,

“No Maas , no mass “ can be heard coming from the opposite corner ..

 

[amirm]

There are some very knowledgeable people posting on this forum. You are not one of them.

Mod: No reason to resort to this kind of commentary especially from our senior members. Let's let the facts speak.

 

[SIY]

The output impedance is still too high though. My guess is that anybody noticing a difference in sound between one of these and a modern conventional SS amp is as likely to be hearing the effect on the frequency response of their speakers of their high output impedance as any distortion products.

In order: yes, but it's unrelated to the (virtual) transformer.
And yes, absolutely. Speakers with stupidly varying impedance curves (I'm looking at you, Wilson) are touted as "particularly revealing of amplifier differences."

 

[Krunok]

Speakers with stupidly varying impedance curves (I'm looking at you, Wilson) are touted as "particularly revealing of amplifier differences."

Indeed - can't help to remember Magnapan .7 when you said that. But they can still be driven correctly and provide excellent sound as long as amplifier's output stage can provide enough current. But if you have an amplifier which cannot handle when impedance falls below 4, or even 3 Ohms, than you better be careful when choosing your speakers in order not to upset your "delicate" amp.

 

[Krunok]

Btw, I'm pretty sure that the +-0.9 dB of the non linearity measured here (black line) before adding the Zobel network to the speaker simulator would also be masked by speaker's own non linearity which is typcaly at least +-3dB in that region, so it won't be heard. What could be heard however are distortions coming from the fact that amp ran out of steam when driving speakers with low impedance, and that is exactly why distortion is raising sky high as delivered power is raising.

When I see this pitiful excuse of a tube amp I have to swear I'll never complaint of my tube amp as comparing the specs mine is a true HiFi reference monster!