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

amirm

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#1
This is a review and detailed measurements of Audio-gd NFB-28.28 DAC, headphone amplifier and pre-amplifier. It is on a kind loan from a member and retails for USD $750 plus shipping from China. The unit is quite heavy so I suspect shipping will cost a few dollars.

This is a deep enclosure but half the width of the larger Audio-gd products:

Audio-gd NFB28.28 DAC and Headphone Amplifier Review.jpg

Navigating the unit is maddening. 7-segment LED digits are used to indicate input number, setting, etc. I searched for the manual but could not find any. Instead there is some random text on Audio-gd website that starts to deal with something about a problem they fixed. How a simple device is made so complicated is beyond me. The unit could stand serious cleaning up of the documentation and revamping of the user interface.

There are lots and lots of inputs and outputs. I let you read the documentation for yourself. For my testing I used the USB input and either balanced XLR output for DAC testing and front 1/4 inch for headphone. Thankfully the DAC was plug-and-play compatible with Windows 10 Creators Edition so I did not need to install any drivers.

When I unpacked the unit, there was something metallic rattling in it. I started to unscrew the top to find out what it was, only to notice one of those stickers on it saying warranty void if opened. This is silly since changing DAC filter setting is done by changing jumpers internally! Anyway, I took a chance and powered it up and seems to be working.

EDIT: see this tear down and cause of that rattle: https://www.audiosciencereview.com/...b28-28-dac-and-headphone-amp.5147/post-115292

Previous to this unit, I had tested and reviewed the Audio-gd NFB27.38. The distortion performance of that unit was exceptionally poor. Some suggested then that perhaps that unit was broken. This unit gives us another bite of that apple. So let's get into measurements and see how she did.

Measurements
There is a switch on the back of the unit that forces the line out to be at fixed level. I activated that and that produced this horror show:
Audio-gd NFB28.28 DAC and Headphone Amplifier Measurements.png


We have large and massive amount of second and third order harmonics respectively. Experimenting with alternate mode of variable output and various gain and level settings did not produce anything better. This produces by far the worst SINAD rating of any DAC I have tested regardless of price:
Audio-gd NFB28.28 DAC and Headphone Amplifier SINAD Measurements.png


This is the same problem I saw in Audio-gd NFB27.38. For that device, they had published far better measurements using audio precision analyzer. The same is true here:

1541566489008.png


We actually see some similarities to my graph with respect to distortion/jitter sidebands around the main tone. But theirs shows far less harmonic distortion. My guess is that this is the performance of the DAC subsystem sans the output stage. And it is the output stage that is adding the copious amount of distortion.

Given the fact that I have now tested two Audio-gd products with two different analyzers, I have no doubt that there are design issues in this product and their measurements do not reflect complete units they ship to customers.

Anyway, continuing with the measurements, lets look at jitter:
Audio-gd NFB28.28 DAC and Headphone Amplifier jitter Measurements.png


Nothing really broken here other than higher noise floor and sidebands that get somewhat too high. Fortunately audibility of all of this is very low to non-existent so not a problem.

Intermodulation distortion versus level reveals same problems we see in our dashboard:
Audio-gd NFB28.28 DAC and Headphone Amplifier IMD Measurements.png


We see much higher noise floor but then a sudden rise in distortion to very high levels.

Linearity is decent since the test removes distortion and noise before reading the level:
Audio-gd NFB28.28 DAC and Headphone Amplifier Linearity  Measurements.png


Usually the right side of the graph is ruler flat and at zero but we see a rise there due to distortion issues.

Let's switch to headphone out and measure power using 300 ohm load:
Audio-gd NFB28.28 DAC and Headphone Amplifier Power at 300 ohm Measurements.png


Whether we use low or high gain, noise and distortion levels are substantially higher than other products.

At this point I am in sufficiently bad mood to not do any more testing.

There is no listening test for that reason and for the fact that I am watching the election news on this machine.

Conclusions
These Audio-gd products are complex and have tons and tons of discrete components. They seem to be camping on audiophile myths that things like feedback are bad. As such, they are providing performance that in my opinion is beyond broken. No way are these models of fidelity or what an audiophile should be chasing.

I am also unhappy that the company provides no usable documentation and continues to show measurements that don't relate to products being sold. Bending the truth in advertising is something, but under-reporting distortion by so many miles is not correct or ethical.

Needless to say, I cannot in any form or fashion recommend Audio-gd NFB28.28. Or frankly any other product they make at this point.

-------------

As always, questions, comments, recommendations, etc. are welcome.

If you like this review, please consider donating funds using Patreon (https://www.patreon.com/audiosciencereview), or upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
 
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BurritoJustice

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#3
Their whole shtick is No Feed Back (NFB in the name) so it isn't super surprising how much of a measurements traincrash they are. They do acknowledge that they will measure poorly but it is very disappointing that they have graphs that are straight up lies.

Audio-gd are insanely popular amongst the audio community so this will disappoint many people. I kinda want to try one as they seem like the solid state equivalent of a tube amp, huge amounts of introduced distortion that people seemingly enjoy. Can't image ever buying one though.
 

bunkbail

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#5
Thanks for the review @amirm. 2 Sabre offerings from Audio-gd measured very badly so it is clear that these measurements weren't a fluke. Do you have any R2R based Audio-gd DACs lined up for review?
 

amirm

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#6
Do you have any R2R based Audio-gd DACs lined up for review?
I don't have any other in the pipeline. But would welcome measuring one of those.
 

BurritoJustice

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#7
Thanks for the review @amirm. 2 Sabre offerings from Audio-gd measured very badly so it is clear that these measurements weren't a fluke. Do you have any R2R based Audio-gd DACs lined up for review?
I feel like the combination of R2R and feedback free design will reach levels of distortion not thought possible by mankind.
 

gvl

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#9
I feel like the combination of R2R and feedback free design will reach levels of distortion not thought possible by mankind.
Well, the probability that distortions from the DAC and the amplifier sections can cancel each other isn't 0.
 

JJB70

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#11
I think I will buy one as anything that measures that badly must sound heavenly if we apply the law of inverse relevance and article 2 of the audiophile code which tells us that all good hifi measures badly. However, we must understand that the potential of a high performance and precision audio master piece such as this can only be realised by hooking upa $1000 USB cable and a $15,000 power chord.
 

Veri

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#12
I think I will buy one as anything that measures that badly must sound heavenly if we apply the law of inverse relevance and article 2 of the audiophile code which tells us that all good hifi measures badly. However, we must understand that the potential of a high performance and precision audio master piece such as this can only be realised by hooking upa $1000 USB cable and a $15,000 power chord.
Don't forget the rubidium word clock.
 

VintageFlanker

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#13
Hum... That's devastating. I owned some AGD products these last two years: DAC 19, NFB 28.38 and R2R-11. I kept none of them (though I have to admit I really liked the warmish "tube" sound of R2R-11). Now, I'm running with an ADI-2 DAC and it's like I just discovered what a clean and neutral sound is.

My experience, in addition to these measurements make things clearer : I will never buy any unit from them again.
 
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#16
Amirm looks quite convinced to see the world burn, I like that. ;)

Thanks for another snake oil advice...
 

restorer-john

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#17
When I unpacked the unit, there was something metallic rattling in it... This is silly since changing DAC filter setting is done by changing jumpers internally...
Are you sure whatever was rattling around inside wasn't a vital shorting jumper for the filter settings and that has compromised the test results?
 

Tene

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#18
Hum... That's devastating. I owned some AGD products these last two years: DAC 19, NFB 29.38 and R2R-11. I kept none of them (though I have to admit I really liked the warmish "tube" sound of R2R-11). Now, I'm running with an ADI-2 DAC and it's like I just discovered what a clean and neutral sound is.

My experience, in addition to these measurements make things clearer : I will never buy any unit from them again.
Same, even though I've never owned one, over the years people made me believe AGD was the holy grail of "budget" audio.
Maybe the beautiful insides biased lots of them :p
 

Grave

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#20
Another shit audiophile brand I have heard of, no surprise here.
 
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