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

JJB70

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Maybe I'm the odd one out here, but in terms of audible, as opposed to measured, performance I find it difficult to find a DAC that isn't transparent. Even the DAC on my mobile phone is excellent (the only criticism I have of the music output is that the headphone output levels can be a bit weak, but that's nothing to do with the DAC). If doing a double blind level matched test I'm guessing most would struggle to discern differences.
 
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Pages and pages of this back and forth devoted to @Bluespower and his a superhuman hearing. @Bluespower, have you considered started a dedicated thread on this subject?

Not trying to be rude, but I'm having trouble finding a polite way to deal with this. After the first few pages, these equipment reviews start to devolve into inane arguments that fly in the face of the spirit of this forum. Maybe review threads are destined to turn to irrelevant rubbish (in relation to the review of the product).

@Thomas savage maybe you have a better way to deal with this, but at this point, what does any of this have to do with the Audio-gd NFB28.28? At what point do we say, "This is a legitimate topic, but this is the wrong place to have this discussion?"

7/17 pages of this "review" are now devoted to @Bluespower and his theories.

@Thomas savage, please, please, please help clean these review threads up.
 

amirm

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I think you are right,
I guess also i'prefer when there is less processing.
On tv also i disable'all,processing on the picture i find it ugly lol :)
Please take further discussion of new tests to a new thread.
 

Thomas savage

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Pages and pages of this back and forth devoted to @Bluespower and his a superhuman hearing. @Bluespower, have you considered started a dedicated thread on this subject?

Not trying to be rude, but I'm having trouble finding a polite way to deal with this. After the first few pages, these equipment reviews start to devolve into inane arguments that fly in the face of the spirit of this forum. Maybe review threads are destined to turn to irrelevant rubbish (in relation to the review of the product).

@Thomas savage maybe you have a better way to deal with this, but at this point, what does any of this have to do with the Audio-gd NFB28.28? At what point do we say, "This is a legitimate topic, but this is the wrong place to have this discussion?"

7/17 pages of this "review" are now devoted to @Bluespower and his theories.

@Thomas savage, please, please, please help clean these review threads up.
Iv deleted 22 posts ( including mine) , yes your right but unfortunately we had a guy asking questions who seemed genuinely to want to know the answers. Iv left the more useful exchanges in tact .

These threads will always attract individuals with varying understandings of Audio and misconceptions will be challenged. Really once the review has been published and the results checked and expanded ( normally the first 10 pages) the rest will probably be irrelevant to a guy like you if it’s hard data your after. Expecting the threads to carry on delivering highly valuable content after their natural conclusion is unrealistic.

I’d have to work 24 hours a day to do that rather than 20 hours a week.
 
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Iv deleted 22 posts ( including mine) , yes your right but unfortunately we had a guy asking questions who seemed genuinely to want to know the answers. Iv left the more useful exchanges in tact .

These threads will always attract individuals with varying understandings of Audio and misconceptions will be challenged. Really once the review has been published and the results checked and expanded ( normally the first 10 pages) the rest will probably be irrelevant to a guy like you if it’s hard data your after. Expecting the threads to carry on delivering highly valuable content after their natural conclusion is unrealistic.

I’d have to work 24 hours a day to do that rather than 20 hours a week.
I hear that, and I'm not trying to hijack this thread for another tangent. I know some forums can split/combine threads, maybe that's an answer?

I understand that there is a limit to technical discussions, but the DX3 thread (not without it's own drama sadly) shows that there can be other issues related to the product that aren't purely technical measurements, but are very valuable to someone actively considering the device.

Whatever the approach, I very much appreciate the work young are doing moderating this forum, and I don't want to discourage @Bluespower from asking these questions as they seem genuine in their curiosity. Thanks for taking time to respond and address the issue.
 

Thomas savage

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trl

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[...]
How about this?:

Go to a recording studio with a highly praised R2R DAC and a good measuring DS DAC. Record some complex music with the mixer set for maximum transparency and dynamic range. Play back the captured file via the DACs and record the output with the same mixer settings. Do a digital nul-test.
This is possible, actually somebody already did that, but for audio streaming services. Seems that there's nothing "in the air" that can beat the original WAVE/FLAC files:
. I like that guy that he has a very good sense on how audio files should sound and he's good enough to prove the differences he's hearing. I believe DACs can be measured in a similar way and the files could be compared in Audition (or invert one of them, then listen to the diff. only).

P.S.: Hope this will not start a new thread like the above DSD one. :) If someone still wants to reply, here's the original post and the thread: https://www.audiosciencereview.com/...udio-content-delivery.5834/page-6#post-131653.
 

Bluespower

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@trl i think the mastering of the file he tests is very compressed. It would be intersting to do the same test with a song that has greater dynamic range. There will be more differences i guess because lossy codecs are compressing the dynamic range. It's easier for them with already low dynamic record.
 

amirm

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I like that guy that he has a very good sense on how audio files should sound and he's good enough to prove the differences he's hearing. I believe DACs can be measured in a similar way and the files could be compared in Audition (or invert one of them, then listen to the diff. only).
You can't test DACs the same way because there, you have to capture analog and with analog, each one will drift differently making any synchronous testing impossible. For his test, he is capturing the uncompressed digital streams so he doesn't run into that.
 

trl

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I though we can do that, as we do with REW, after all we hear the analogue signals and not the digital? I was referring to testing the RCA/XLR output of DAC units, not the SPDIF/TOSLINK ones.
 

Thomas savage

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Please read this https://www.audiosciencereview.com/...d-discussion-and-moderation-please-read.5936/

Iv no clue where this DS vs R2R discussion originated on this thread, if you want to carry it on give me all the post numbers and I will transfer it out to a appropriate thread.

Otherwise it’s now over and we are getting back to the OP. I’m issuing a reply ban for member @Bluespower as clearly there’s no intrest in talking about the review .

Edit.
Iv moved a bunch of the DS vs R2R to here https://www.audiosciencereview.com/...”-what’s-the-big-deal.5359/page-6#post-132945

Iv gone through the whole thread and moved a bunch more , about 20 of the DS vs R2R moved out now .
 
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I measured the rear fixed output on my NFB-28.38 with an oscilloscope and it was indeed shockingly bad, but I wasn't surprised, because it was 30V (on S mode), which is an insane amount. You can fully drive most power amps with 1.4 Volts. Before I sell my 28.38 (!) can the OP confirm that you did testing with the rear button not enabled, that is, in variable mode, and on a sensible gain and volume (for example, high gain (H) at 40 volume, or something like that)?

Also if this distortion does exist at power levels that would be reasonably used, could it have damaged my headphones or speakers or power amp? I'm guessing and hoping not.

By the way I disagree, I think the device is easy to use.

Thanks
 

trl

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@concorde would you mind uploading some pics with how signal looks alike on the outputs?
Also, power rails would be interesting to visualise as well, not only the 3.3V and 5V, but also the +/-12...15V (don't know what voltages are inside this NFB-28.38 to power the discrete "opamps").
Ideally would be to limit scope's measurements to less than 1MHz...100KHz perhaps, but any measurements will be fine anyway.
Thanks!
 

amirm

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I measured the rear fixed output on my NFB-28.38 with an oscilloscope and it was indeed shockingly bad, but I wasn't surprised, because it was 30V (on S mode), which is an insane amount. You can fully drive most power amps with 1.4 Volts. Before I sell my 28.38 (!) can the OP confirm that you did testing with the rear button not enabled, that is, in variable mode, and on a sensible gain and volume (for example, high gain (H) at 40 volume, or something like that)?
I have the scope output in my review:



It is 5.5 volts RMS which is a bit hot relative to 4 volt output we see on most devices. But should not cause saturation especially since the manufacturer had programmed the level.

Here is Benchmark DAC3 at far higher levels with superbly low distortion figures:




Output is twice as high yet distortion is a whopping 55 dB lower!

Headphone measurements were done using the appropriate jack and from low to high levels.
 
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@trl Hi, I don't think I have the equipment necessary to look at signal quality properly. I was just looking at peak to peak voltage, using test frequency tones, and at 30V output it was a very distorted graph, but at <10V it looked like a good sine wave. I did the measurements several months ago by the way. I don't really want to set it up again right now sorry.
 
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@amirm Thanks for that, looks like I'm gonna replace the unit with something else.

I will need a DAC; and a HP amp with balanced/nonbalanced HP outs; and pre-amp with balanced/nonbalanced pre-outs. Whether the DAC and amps be separate units doesn't matter to me. But I want at least the HP amp and pre-amp to be the same unit. Also I need a way to know when I've reached 1.4V (line level) on the pre-out, so that I don't hurt my power amp (Crown with a sensitivity of 1.4Vrms). Budget is about 1100 USD. Any suggestions?

The RME ADI-2 DAC looks really promising (it can drive inefficient headphones I believe?) and it has XLR outs, but it doesn't seem to have a balanced headphone out? I have the TH900 headphone with a balanced cable so I'd like balanced out.

Note: (For my nfb-28.38 I measured, with an oscilloscope, that on high gain, the pre-out reaches 1.3-1.4 V at a volume of "34", so I made a note to never turn it above 34 when using as a pre-amp.)
 

amirm

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For the amp, looking into massdrop THX AAA 789. It has both balanced and unbalanced (for inputs and outputs). Not sure if it meets your requirement for a pre-amp so look at that functionality. For a DAC, SMAL SU-8 V2 is a good pairing with balanced output. Combined it is less than $600.
 
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