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Author Topic: Audio-GD NFB2 DAC Measurements  (Read 1590 times)

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firev1

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Audio-GD NFB2 DAC Measurements
« on: February 16, 2014, 12:23:44 PM »
One of my audiophile friend was generous enough to lend me a couple of DACs to hear and measure. According to him, its a warm and analogue DAC and I agree(to me a little tubey like?). This DAC is the first batch or version of the NFB2 without filter jumpers and it has been set for 4x OS with a soft knee linear phase filter.

http://www.audio-gd.com/Pro/dac/NFB-2/NFB2EN.htm

Test Setup:
Fujitsu Lifebook-> usb-> SB1240->optical cable(reasonably built it seems) -> NFB2 loopback
and
Acer Aspire V5 122P Win8 laptop->printer cable -> Audio-GD NFB2-> shielded RCA cables-> SB1240 line in-> usb cable with a ferrite choke on the device side-> Fujitsu Lifebook (for jitter test of USB)

Test conditions:
AC power in laptops, no tweaks except for service shutdowns
0dbFS at 2040mV was used for the test. Highest signal levels used for most test are -3dbFS

24 bit 48khz sampling rate unless stated otherwise, all test run@48khz

Jitter: For a dac today, I think its pretty poorish? Sidebands at -105dbFS can be seen. Poor jitter rejection of the Tenor 7022 as well reminds us that DACs back then have shitty usb implementations, clearly the optical outperforms it.

I could test the coax performance but I don't have a 75ohm digital coax cable on me right now and also no "low jitter" transport. Does a Sony BDP-S380 count :P ?

Distortion: Not really good in todays standards but with lower signal levels, I could extract much better THD performance out of the unit by not stressing the output stage. Also the benefits of a non feedback design can be seen here; virtually zero D6+ distortion. Too bad I could only test this sometimes as Steps or this method requires that the clock from output to inputs be the same  :)p12

Low resolution performance: As you guys can see, pretty noisy plots but I wonder sometimes whether it matters, need to hear more of this DAC. Some DC shift(is it) can be seen in the zoomed out plots, did not notice this with the SB1240 and Herus. I think the Stoner Acoustics UD100mk2 shows this phenomenon as well. Wonder how it impacts sonic performance.

CCIF High frequency performance: Pretty decent looking, I really expected it to be worse considering the filter.

RMAA test files below, the SMPTE test disagrees with ARTA, wonder why.
« Last Edit: February 16, 2014, 12:59:43 PM by firev1 »
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Re: Audio-GD NFB2 DAC Measurements
« Reply #1 on: February 16, 2014, 03:28:25 PM »
Interesting! Right away, I see measurements have that slightly "noisy" quality to them much like my NOS1704. Do you hear any background noise/hiss with this DAC? And the page you linked says it has selectable filters. Do you know what the DAC is currently set at?
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Re: Audio-GD NFB2 DAC Measurements
« Reply #2 on: February 16, 2014, 11:10:28 PM »
Not to sure I heard it in the brief time I had listening to it (via optical). The dac itself has pretty marginal noise performance due to its use of nearly all through hole components.

The filter settings are mentioned in the first para, linear phase soft knee 4X oversampling.  Frequency response show that it has early rolloff somewhat.

On another note, my friend found what seems to be the jumpers >_< so I might be able to change filters.
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Re: Audio-GD NFB2 DAC Measurements
« Reply #3 on: February 17, 2014, 04:52:59 AM »
LOL, my bad for overlooking that. I'm curious to see if you can indeed change the filter settings.

The NOS1704 I have has noise that can be heard with sensitive headphones and amps if you turn the volume up beyond where you'd normally listen. In that sense, it's not much of an issue, but measurements show it does seem to impact its ability to resolve the -90dB 1KHz sine wave test. However, it's hard to get the NOS1704 measurements perfect, because the unit outputs at either 1.25V or 2.5V. It becomes an issue with voltage/volume matching, especially when using ASIO doesn't always give you control of volume settings. I get noisier measurements at the low voltage setting, generally, but the high voltage setting can be hard to match...without matching, it just adds tons of distortion at the ADC.
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