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

[andreasmaaan]

Well you just don’t want to burn ya arse...

What novel use of tubes are you referring to here, Thomas?

 

[Thomas savage]

What novel use of tubes are you referring to here, Thomas?

Well I just assumed what with guys fascination with all the diffrent shapes,, my bad .

 

[andreasmaaan]

Qutest is the one that outputs at 2V, ~1 dB louder over the ADI 2 should make it sound better but @VintageFlanker said he preferred the ADI 2.

That's true, but given the test was done sighted, it's a moot point.

 

[mshenay]

The ADI-2 should sound no different from the Hugo 2. They both have a SINAD of well over 100dB, so any distortion/noise they produce could not possibly be audible. The only possible difference will be the RME's higher output power, although it sounds unlikely you'll need it given you're coping ok with the NFB 10ES set to low gain.

Are both Dacs FPGAs?

Also implementation varies from dac to dac, so I doubt they will sound alike as I imagine each has a slightly different implementation and each handles power differently. Part of why I didn't like the Hugo 2 could have been noise, as I could never quite "silence" it even with a power conditioner

though I didn't have the Etir so there could have been some noise via USB

 

[andreasmaaan]

Are both Dacs FPGAs?

Also implementation varies from dac to dac, so I doubt they will sound alike as I imagine each has a slightly different implementation and each handles power differently. Part of why I didn't like the Hugo 2 could have been noise, as I could never quite "silence" it even with a power conditioner

though I didn't have the Etir so there could have been some noise via USB

I don't know whether these DACs use FPGAs. But although these questions are important from a designer perspective, they are irrelevant in terms of the end product. Noise and distortion below -100dB can't be heard, regardless whether it comes from the power supply or elsewhere.

I'd be surprised if the noise you heard was coming from the Hugo though. I can't see how a power conditioner could help with this. Was the noise present when you used other DACs without making any other changes to the setup?

 

[maverickronin]

Are both Dacs FPGAs?

The ADI-2 DAC uses an FPGA for some of it's DSP functions (it also has a standard DSP chip as well) but the actual conversion is handled by an AK4490.

 

[mshenay]

I don't know whether these DACs use FPGAs. But although these questions are important from a designer perspective, they are irrelevant in terms of the end product. Noise and distortion below -100dB can't be heard, regardless whether it comes from the power supply or elsewhere.

I'd be surprised if the noise you heard was coming from the Hugo though. I can't see how a power conditioner could help with this. Was the noise present when you used other DACs without making any other changes to the setup?

I believe the noise was a combination of the system. As when I fed the Hugo into my Tube I got literally FM reception, but when I run the same amp with any other dac portable or not No noise... soo the Noise was unique to my system. An ironically I had a similar issue with some iFi Products while in that location as well...

The ADI-2 DAC uses an FPGA for some of it's DSP functions (it also has a standard DSP chip as well) but the actual conversion is handled by an AK4490.

Ahh well then I guess the Hugo 2 an ADI-2 Dac must just measure similar. Still different I'm sure the circuit design and firmware are different, so no reason to expect that each would sound the same even though the have similar objective performance

 

[Krunok]

Ahh well then I guess the Hugo 2 an ADI-2 Dac must just measure similar.

And how exactly do you think FPGA can affect SQ?

 

[mshenay]

And how exactly do you think FPGA can affect SQ?

Depends on how it's programmed, do all FPGA operate the same in every circuit? I imagine the design team would program the FPGA to respond to the needs of that circuit.

You also quoted only a portion of what I wrote, another member mentioned the Hugo 2 and ADI-2 Dac should sound the same, to counter his point I asked if both were based entirely around FPGA implementations.

An they are not, the ADI-2 Dac has the AK 4490 at it's core with a FPGA handling some of the DSP functions in addition to a dedicated SOC for it, where as the Hugo 2 from what I understand is entirely an FPGA based DAC. So how can the sound the same? How could this member even reach that conclusion, I assumed that MAYBE the have similar measured outputs or results. So my point was to dismiss any notion that the Hugo 2 and ADI 2 dac sound "the same" as he presented no real reason. Maybe if he had measurements of both and some subjective listening WITH both, I'd entertain the thought. But he didn't and that's ok!


Now, to answer you question which has no baring or context on my point,

How do I think an FPGA can affect sound quality? I think how it's programmed will likely have an impact on sound quality, I also think how power is handled by the System as a whole will also affect how the FPGA operates and ultimately how it can affect the sound quality.

 

[Deleted member 65]

I had one of those at one point actually. I think it was Ref 7, maybe Ref 7.1. Anyway, the original one that had 8 x PCM1704.

I quite liked it. Very weighty, solid kind of sound was my impression, although not the cleanest/clearest (that's obviously to be taken with a grain of salt so many years later). It seemed to suit my system well at the time, which was a bit lean due to the room/speaker combination I had, but I wouldn't particularly recommend it in general.

Also had one (Ref-5 w. 4*1704's), not bad but now in the possession of my son. Adaptive USB made me look elsewhere.

 

[Veri]

@mshenay I think you are a little misguided about what defines how something will sound.

Once devices output >100db (possibly much lower!) signal over noise, with of course little harmonics in the signal, these devices should sound theoretically very damn near identically similar, we aren't bats! If there is no 'color' = distortion added to the signal, there should be no audible difference, but instead be transparent.

As long as there no obvious flaw such as EMI noise or vibration(think chord Mojo) affecting sound, you should really just shop for the features, convenience and/or power a device offers

 

[andreasmaaan]

@mshenay what @Krunok and I are pointing out is that both units produce no distortion or noise that is louder than 100dB below the signal. It’s not possible to hear anything that low in level due to the noise floor of any domestic listening room, the noise floor of recordings, and above all, the limits of the human auditory system.

I guess there was an issue with the way your Hugo interacted with your tube amp or some other device in your system, so of course in that case you were able to hear noise that shouldn’t have been present. I’m not sure why that was the case, as all measurements I’ve seen of the Hugo 2 have shown a noise floor below any level that could be audible under normal circumstances.

 

[mshenay]

@mshenay I think you are a little misguided about what defines how something will sound.

Once devices output >100db (possibly much lower!) signal over noise, with of course little harmonics in the signal, these devices should sound theoretically very damn near identically similar, we aren't bats! If there is no 'color' = distortion added to the signal, there should be no audible difference, but instead be transparent.

As long as there no obvious flaw such as EMI noise or vibration(think chord Mojo) affecting sound, you should really just shop for the features, convenience and/or power a device offers

@mshenay what @Krunok and I are pointing out is that both units produce no distortion or noise that is louder than 100dB below the signal. It’s not possible to hear anything that low in level due to the noise floor of any domestic listening room, the noise floor of recordings, and above all, the limits of the human auditory system.

I guess there was an issue with the way your Hugo interacted with your tube amp or some other device in your system, so of course in that case you were able to hear noise that shouldn’t have been present. I’m not sure why that was the case, as all measurements I’ve seen of the Hugo 2 have shown a noise floor below any level that could be audible under normal circumstances.

I still have to disagree to an extent, I've had experience where firmware updates make noticeable changes in sound as do "filters" and I believe Rob Watts has a some very cool but unique idea's about how sound is processed. So again I imagine how their processing that basic signal also has an impact on how things sound. there's also the matter of the output voltage, on the Hugo 2 it's... fixed but you can technically adjust it since there's no "amp" in the traditional sense on the Hugo 2. An going back to filters as a matter of fact I did run the Hugo 2 with one of it's variable filters.

But I see and agree with your "theoretical" point, but you know that things tend to differ in practice than in theory or in a lab

Going back to the noise your are correct. It was unique to my system, but others have also had an issue with the Hugo 2 having noise in their systems. So my problem with the Hugo 2 is entirely related to how it operates in my system, when introduced to noise unique to my system. I also feel it's portable and stay at home design has some unnecessary limitations as the unit I used also ran incredibly hot, yes it was "supposed to" cool down after 24 hours of continuous use but did not. I had even more noise when charging it as well.

Since then, I've made some major changes in my home system and I'm not living in my old Apartment building that was a quarter mile or so from a Radio Station.

Now as for the ADI 2 Dac, it's design seems to be focused on functioning in existing system in addition to having it's own headphone out. So I'm more confidant in it's performance because of how well it's been reported on from a variety of people, in a variety of systems and rigs it consistently get's praise. So it would seem the design of the ADI-2 Dac is maybe better at preserving the quality of said signal especially outside of very carefully crafted measurement environments. Where as the Hugo 2 in my an others' experience was more susceptible to degradation unique to the individual rig

But maybe it won't matter, maybe I won't like the ADI 2 Dac either! I'll have to get it and play around with it, though I think I'll have a better experience with it based purely on it's design. I couldn't even run the Hugo 2 via Coaxial at the time I reviewed it since I didn't have a 3.5mm Coax Cable, only RCA.

 

[Jimster480]

It's very hard to know I guess. I'd be extremely surprised if there's any actual peaks in the Qutest's frequency response, that is very unusual in a DAC and is certainly not Chord's style.

In most of these cases psychology or level imbalances between the two units (not necessarily loud enough to be consciously perceived as a difference) tend to be the decisive factors IMHO (I apply this thinking to myself too btw).

1.8V vs 2V is a difference of almost a decibel which is definitely enough to make one sound better than the other.

I do have to say that I have been able to hear differences in hardware. Between Amps and DAC's even (although most DAC's sound the same as long as they perform well) going back and forth between the two you can sometimes hear something that is different in specific songs.
It could be due to the output stage, etc but there are differences in products, because SINAD is just one number.

 

[Addicted to music]

All of those through hole film capacitors (Wimas?) for supply decoupling on SMD chips also puzzles me. Sure, the red caps on a black PCB looks pretty, but high quality ceramic SMD caps would be a far better choice.

Can I ask,

Why a high quality ceramic or any SMD ceramic would be a better choice for audio? Not exactly a fan of ceramic caps unless it’s for RF.

 

[andreasmaaan]

I do have to say that I have been able to hear differences in hardware. Between Amps and DAC's even (although most DAC's sound the same as long as they perform well) going back and forth between the two you can sometimes hear something that is different in specific songs.
It could be due to the output stage, etc but there are differences in products, because SINAD is just one number.

Ok, but are you doing this blind and level-matched? What are some examples of DACs you and amps you can hear differences between?

SINAD is just one number, but that still doesn't explain how someone could be able to hear something 100dB below something else, a feat which has never been demonstrated to be possible under controlled conditions.

 

[andreasmaaan]

I still have to disagree to an extent, I've had experience where firmware updates make noticeable changes in sound as do "filters" and I believe Rob Watts has a some very cool but unique idea's about how sound is processed. So again I imagine how their processing that basic signal also has an impact on how things sound. there's also the matter of the output voltage, on the Hugo 2 it's... fixed but you can technically adjust it since there's no "amp" in the traditional sense on the Hugo 2. An going back to filters as a matter of fact I did run the Hugo 2 with one of it's variable filters.

Of course adjusting filters and firmware could impact on sound quality, but it really depends on the device and the settings. Have you taken steps to be sure that these noticeable changes were not psychological?

Rob Watts' ideas about how sound is processed are certainly unique, but there's no sound theoretical basis to them and no experimental evidence of their validity to boot (and there probably never will be since his theories are incoherent, to be frank).

Now as for the ADI 2 Dac, it's design seems to be focused on functioning in existing system in addition to having it's own headphone out. So I'm more confidant in it's performance because of how well it's been reported on from a variety of people, in a variety of systems and rigs it consistently get's praise. So it would seem the design of the ADI-2 Dac is maybe better at preserving the quality of said signal especially outside of very carefully crafted measurement environments. Where as the Hugo 2 in my an others' experience was more susceptible to degradation unique to the individual rig

But maybe it won't matter, maybe I won't like the ADI 2 Dac either! I'll have to get it and play around with it, though I think I'll have a better experience with it based purely on it's design. I couldn't even run the Hugo 2 via Coaxial at the time I reviewed it since I didn't have a 3.5mm Coax Cable, only RCA.

I agree, that ADI-2 DAC is a superb device when it comes to interface and features. By far my favourite DAC/headphone amp.

Amir's measurement environment is not carefully crafted btw. He just uses his pretty standard laptop, cheap cables, standard wall socket, no power conditioning, etc.

 

[Jimster480]

Ok, but are you doing this blind and level-matched? What are some examples of DACs you and amps you can hear differences between?

SINAD is just one number, but that still doesn't explain how someone could be able to hear something 100dB below something else, a feat which has never been demonstrated to be possible under controlled conditions.

No there is realistically no way to do blind or perfectly level matched testing. It requires having multiples of each piece of gear with a complex set of quick-switches and also special gear to know the voltages are exactly the same.

For me I just get a tone in a song or just a tone file and then I level match between the two devices. Then I'll play a specific part of specific songs for a few seconds and switch to the other component and then play the same few seconds again. And I'll go back and forth and see if I can notice anything different between the two.

I can tell you that in switching OpAmps in my A30 (I have 2x A30) the sound quality can degrade where complex parts of certain songs lose details.
I tested a $10000 Tube amp that supposedly had a "huge soundstage" and I was able to tell the difference between it and my A30/O2 and figure out that the "magic 10k amp" was just rolling off certain frequencies and smoothing out a few lower level details.
I also tested the Soundaware P1, and its hard to say what it sounds like because its "pleasant" but it sounds nothing like my A30 or O2.
The sound simply is just different overall, seemingly more forward maybe? I couldn't detect any frequency rolloffs though using any of my test tracks or tones.
In testing the Massdrop Liquid Carbon I found that it simply creates a more bassy tone in music. We tested this with my Aeon, my friends Auteur, HE-6, and my Oppo PM-2 & Denon Ah-MM400. Every song had more bass with this amp somehow, although I didn't detect any roll offs either with my test tones or tracks.

See when it comes to my method of testing, while I'm not using testing hardware... my ears have so far been right based on Amir's measurements that have come later
I remain objective and really don't have any bias based on price, claimed performance, etc
I simply try to listen for details, dynamic range, etc
Since I have read about our brains only being able to remember upto around 7 seconds of audio I usually try to keep my tests around 5-10 seconds and switch quickly (or have someone else switch for me).

 

[Krunok]

Depends on how it's programmed, do all FPGA operate the same in every circuit? I imagine the design team would program the FPGA to respond to the needs of that circuit.

You also quoted only a portion of what I wrote, another member mentioned the Hugo 2 and ADI-2 Dac should sound the same, to counter his point I asked if both were based entirely around FPGA implementations.

An they are not, the ADI-2 Dac has the AK 4490 at it's core with a FPGA handling some of the DSP functions in addition to a dedicated SOC for it, where as the Hugo 2 from what I understand is entirely an FPGA based DAC. So how can the sound the same? How could this member even reach that conclusion, I assumed that MAYBE the have similar measured outputs or results. So my point was to dismiss any notion that the Hugo 2 and ADI 2 dac sound "the same" as he presented no real reason. Maybe if he had measurements of both and some subjective listening WITH both, I'd entertain the thought. But he didn't and that's ok!


Now, to answer you question which has no baring or context on my point,

How do I think an FPGA can affect sound quality? I think how it's programmed will likely have an impact on sound quality, I also think how power is handled by the System as a whole will also affect how the FPGA operates and ultimately how it can affect the sound quality.

Heh, "needs of the circuit"..

Do you have an idea what actually FPGA does in DAC device? What is its role?

Or even better, take a look here and try to imagine what possible effect could FPGA ahve on SQ..

 

[andreasmaaan]

See when it comes to my method of testing, while I'm not using testing hardware... my ears have so far been right based on Amir's measurements that have come later
I remain objective and really don't have any bias based on price, claimed performance, etc
I simply try to listen for details, dynamic range, etc
Since I have read about our brains only being able to remember upto around 7 seconds of audio I usually try to keep my tests around 5-10 seconds and switch quickly (or have someone else switch for me).

Fair enough, you're being rational and realistic about all this and maybe not testing things in a way that's scientifically rigorous but doing a few things you can do without turning your home into a test lab

The issue for me still remains this one though: how can a person possibly hear anything 100dB below the signal?