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mowglycdb said:

Just recieved the NFB-6 yesterday, I left it burning in at home, hopefully I'll get the balanced cable before new year and I'll give new impressions.
 
It's sounding okay out of the headphone jack   but there's something missing, it sounds a little be veiled and trebles seem a bit brittle. The amp isn't very dynamic,  though they give my LCD-2 a lot of juice. Hopefully I'll change my view with burn in and using the balanced output.
 
¿Is there a diference in power between normal jack and balanced output?
 

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Yes, give it a week of heavy use. 

Thanks for the heads up. Btw I'm using it   USB > NFB-1.32 DAC <->  ACSS cable <-> NFB-6  ,  so it should be fully balanced mode when I get the XLR cables
 

Yep, that's the best operating mode
 
That's a nice setup too ^^

At least for now, it seems okay with head phones, but it sounds real good as an pre-amplifier, using it to feed Edifier T1900III, packs a lot of punch

The difference between the sound of this amp single ended vs. balanced XLR is like night and day.  Unbalanced the sound is exactly as you describe veiled and with brittle treble.  Balanced and with burn in, it's incredibly detailed and uncolored.

Thanks for the info, I was actually starting to "not" like it  because in some frequency ranges there's a lot of detail missing and it's harsh.
 

Here is a new member of the NFB-6 club To answer my own question: NFB-6 sounds significantly more neutral than C-2.1 in the same setup. C-2.1 tends to be more on the warm side. NFB-6 is currently somewhat grainy and imaging is not spectacular. But this is out of the box and using SE. Next week I am planning to go balanced with my D2000 and will post more impressions. Let the burn-in rollercoaster start! 

A question for NFB-6 owners using balanced headphone connection: I have reterminated my headphones with Neutrik NC4MXX but it does not lock to the connector on the amp (it can be unplugged without pushing the lever). Anyone having similar situation? I have no issues with the playback or SQ, but it seems strange it does not lock, because both the headphone and amp connector are Neutrik...

The NC4MXX might not lock due to it's different locking type- the ones I use have a "window" (I use NC4MX with my balanced AGD amps)

Yes, you are right: NC4MX has a window trough the metal barrel and NC4MXX has a pit inside the barrel. No big deal, but I was scratching my head in confusion 
 
I have read somewhere that NC4MXX is of the higher quality than NC4MX, but this might be completely wrong...

Maybe that is audiophoolery- it transmits the signal just as well I would bet.

I'm going to use the pre-amp with a M-Audio Studio Monitors that have a XLR 20Ohm input...     will the pre-amp work well with those cans?
 

Been a while....life has gotten in the way the last 4 months.  
 
Just wanted to post a quick update.  The NFB-6 is wonderful sounding as a preamplifier.  After several hundred hours of usage, I am hearing things that I haven't heard with my other preamps, and it really delivers the detail in a non-clinical fashion - the music seems to flow freely, and I always find my toes tapping.  I haven't had much of an opportunity to listen to the headphone stage yet, but a quick listen single-ended was reasonably good sounding.  I don't currently have a set of balanced cans, but I will be starting the search soon.  
 
King-wa did an excellent job on this preamp.  Even if there was no headphone stage, this preamp would be worth way more than it's asking price.  I have a $3K preamp here that has lost it's position as my main preamp.  Well done.....bravo!  

Sorry to zombie a thread, but I didn't want to start a new thread when this one's already here . 
 
I was initially looking at an NFB-28, but since it looks like I might be able to swing for a Lynx Hilo, I just wanted to get an amp for balanced operation only (and not have to sell off any organs to do so), and I've got to say I'm pretty intrigued by the NFB-6. I've read everything I can find here and anywhere else Google can take me (including trying to read the Google Translate versions of the actual Audio-gd forum in Chinese), and I had a couple of quick questions if anybody might be able to help out: 
 

1. I read somewhere that the NFB-6 was based on the amplifier section of the Master 6. Is that correct? 
2. I know that there is a large discrepancy between the performances of the SE and XLR headphone outputs-- but is there a similar discrepancy on inputs? If everything works out, I'm hoping to run a few different sources into this to compare, and half of them are RCA only. So is there any performative disadvantage to using the RCA inputs (converted to XLR HP out, of course)? 
3. Has anybody had a chance to compare this with the other popular, less-than-astronomically priced balanced amp, the Mjolnir? If so, may I ask for your thoughts on how the two compare? 
4. If I have enough bread left after the Hilo to snag one of these, I'm intending on asking Kingwa to go with the voicing that provides the most neutral, transparent sound signature. (I read that he changed it after Frank's review). I read that this simply a matter of changing the biasing of some of the components. First, anybody heard both the original and the changed, 'warmer' versions and care to comment on the differences? Second, is my request a reasonable one to ask of Kingwa, or would it require some major overhaul to do? 
5. Lastly, it seems like this thing is an absolute goldmine for someone looking for an excellent balanced amp at upper-entry-level pricing, but there just aren't many impressions out there (and I've re-read them all several times at this point). Anybody want to share any additional thoughts they've had about the NFB-6, good or bad, since they've had it? 

 
Thanks in advance for any wisdom you gents feel like sharing!! Look forward to reading your comments! 

Hello Theo. 
 
Feel free to zombie the thread anytime.  You are welcome. 
 
I have had the NFB-6 in my system for a short while, about 1 1/2 years ago, so it probably means that I was one the earlier buyers, although not as early as Frank-I's first -and only- Head-Fi review. I believe, although I cannot be 100% certain, that the unit I purchased had already undergone that said fine tuning of the SQ. Either way, I have found the NFB-6 to be essentially neutral, quite transparent and dynamic, with just a hint of the -supposedly- trademark "Audio-GD warmth". It is very mild, and certainly not your typical Valve (read: Tube) warmth, resulting of large amounts of harmonic distortion. It would probably be best described as smoothness, rather than warmth. 
 
As a Pre-amp, as many others have also found, it is a veritable bargain and performs well above its price point, comparing favourably to some very high quality and considerably more expensive Pres such as the fully Balanced Onkyo P-388f/ P-3890, one of the very best classic Japanese designs. I no longer own it, but it has left me with many fond (aural) memories. In that role alone it is more than worthy of its modest admission price. I have run it with at least one Balanced and various Unbalanced sources and I have frankly struggled to perceive any substantial qualitative gap between them. If I understand it correctly, Audio-GD's more recent designs apply their Proprietary ACSS circuitry to the Unbalanced sources after Input, effectively balancing them internally and thus narrowing any performance gap between these and the ACSS proper and XLR inputs. 
 
So why haven't I kept it? Quite simply, I have found its Single-ended Out (6.3mm) much too weak to feed High-impedance Headphones, especially in the case of my 600 Ohm Beyerdynamics. It just does not have the power -and voltage swing- required to drive such Phones. Even with 250/300 Ohm, High-gain is mandatory and one is not left with a lot of Headroom, although admittedly I do listen fairly loud most of the time. I cannot vouch for the Balanced (4-pin XLR) Output, since I have never had any Balanced headphone. I am quite convinced that it will perform much better in that mode, and its power ratings would point to that, being Four times more powerful than in Single-ended mode. Users repeatedly report that it sounds far better in Balanced mode and I am quite sure that it is indeed the case but I am quite confident that the difference is mostly attributed to the vast difference in Output power. I have tested it with a lower-impedance headphone, the Shure SRH-840, and the NFB-6 provided the best performance from this popular model that I ever listened to. I wasn't able to replicate this quality from it since -or before- therefore I have sold it. Had I kept the NFB-6, I would surely still own it...
 
Just to be clear, all the (few) negatives apply only to the 6.3mm Output, not the Single-ended Pre-amp Ins and Outs. 
 
I hope you will find this helpful.
 
All the best,
 
Leonel