It's early days so I'll come back and update this review later, but having just picked up and tested out my new NFB-5.2 I'm very impressed!
Out of the box, the sound from the NFB-5.2 is clean, well separated and layered and laid on a beautifully dark background. Every sound steps forward beautifully through each set of headphones I've tried so far.
In: Coax, Optical, USB
Out: Stereo RCA (i.e. can be used as DAC only)
HPO: 6mm stereo jack
The front panel presents only a few buttons and a large, brushed metal volume knob. Other than the power button, there are four other buttons:
Filter (called "Flavor" on the NFB-5) - alters the filtering used for high frequency roll-off, etc.
DAC/HP - selects the use of the HPO or RCAs. Each can be used with or without the OPA engaged (i.e. straight-thru or with OPA "colouring")
Gain - simple hi/lo option for a +0dB or +12dB output
Input - selector for optical, coax, or USB input
I'm not trying to use all "C" headings, it's just turning out that way!
The NFB-5.2 works with sampling up to 192kHz. I have only tested it with 44/16 and 96/24 and haven't really had time to do any thorough listening, but can confirm seemless operation running USB out of my Windows 7 (64-bit) laptop.
Before the computer would recognise the NFB-5.2 I had to install the 64-bit drivers which were kindly supplied by the team at Addicted to Audio where I bought the NFB-5.2. From some previous reading, I believe some systems might automatically recognise the NFB-5.2, but not 64-bit systems it seems.
What It's Driven So Far...
So far I've tested the NFB-5.2 with:
Ultrasone HFI-680s (75 ohm). It drives these happily on low or high gain (volume at around 50% on low gain for an energetic, but comfortable volume).
The control that the NFB-5.2 brings to the HFI-680s is excellent. They can tend to get a bit "soft" around the edges from lower quality outputs, but the NFB-5.2 sounds tight, controlled, accurate and detailed - really brings the HFI-680s alive.
HiFi-Man Re272s (20 ohm). On low gain, the Re272s sound great at just 25-30% volume.
The NFB-5.2 opens up the soundstage of the Re272s and helps to unleash their beautiful ability for details and smooth musicality. It doesn't do much for the bass response, but that's exactly how it should be. The power, separation and control is improved, but there doesn't seem to be a perceptible shift in the sound signature when using the NFB-5.2.
Shure SE535 Ltds (36 ohm). On low gain it's hard to comfortably get above 25-30% volume.
The hyper sensitivity (119dB) of the Shure's can be as much a blessing as a curse and with the NFB-5.2 it's a mixed bag. The NFB-5.2 brings the magic out of the 535s once the music's cooking, but there's a distinctive background hum when the sound level drops. To give an indication of what I mean, when I first plugged in the 535s I was listening to Dave Matthews Band "So Much To Say" (from Crash). I heard the hum during the beginning and had to turn the volume right down to work out if it was background amp hum from their guitars in the recording or from within the NFB-5.2. Unfortunately it was the latter...
The SE535s really benefit from amping (for the sake of precise sound, not a need for power), but the NFB-5.2. is probably overcooked for the 535s - I'll stick to the portable amp for them.
Recognising that it's early in my journey with dedicated headphone amps, the NFB-5.2 definitely strikes me as great value for a versatile DAC/amp combo. At under $500, the sound quality is outstanding and it brings great texture, clarity and control to my headphones without altering the sound signature in any noticable way. Once I play with the OP stage and filtering I might add more, but for now I'd still be 100% satisfied even if it didn't have that feature!
UPDATE: 9th August 2012 - noticing a sharp electronic "crack" coming through the NFB-5.2 anytime I alter settings on my mdeia player (MediaMonkey). I never had this issue with my Sound Blaster X-Fi so this seems to be an issue brought about by the NFB-5.2. I think the issue may be in the computer hardware/software, but the NFB-5.2 is "reporting" it where the X-Fi doesn't.
UPDATE: 17th August 2012 - with further testing, this is a WASAPI driver issue. ASIO drivers solve this issue and work better.
After several years of break, recently I have re-discovered an audiophile in myself. Needles to say, I am completing my set of gear from scratch and have no alternatives for reference. I wanted the dac/amp combo to drive Denon AH-D5000s, as I felt my PC's soundcard was not doing them any justice.
Luckily I was able to find a local store that stocks quite a lot of high-end equipment and managed to listen to several amps within my price range. The NFB-5.2 sounded as good as some amps twice the price, so I ended up getting it.
What I took home was the display unit that I listened to - that gave me a considerable discount, but also the suspicion that the set is incomplete: apart from the power and USB cables there was nothing else in the box, not even the optical cable that Audio-gd typically includes. Looks like it's the vendor's fault though. But in reality nothing else was needed: I plugged it in and that was it: Windows 7 has recognised it instantly and did its thing without needing any drivers.
The difference it made is worth every penny: the sound is spacious and detailed, the amp doesn't produce any audible noise or distortions even at deafening sound levels, the dac works very well with all the sampling rates I could find, including 24/192. The only drawback is that it makes all the recording flaws more obvious, especially distortions introduced by signal clipping.
I have re-wired also my active speakers to feed off the line-outs. Even that made a massive difference that was instantly obvious, even though the speakers are quite ordinary.
Inputs (USB/optical/coax) are selectable from the front panel. I have tried them all, but couldn't tell any difference. This may be handy if one has multiple sources, otherwise whatever works.
Overall I'm very happy with this combo: it does what I need it to do and does it very well.