Audio Gd has been a favorite manufacturer for headphone fans having developed a reputation of building amplifiers and other products to very high standard at a reasonable price and the NFB6 follows in the same tradition. The NFB6 is built to a price point but it appears to have been designed in the same tradition as all Audio GD products.
It has 5 inputs and is fully balanced. It can be used either with a DAC or CD player in either balanced or single ended mode. It can also be used as a standalone preamp. The retail price is $400.00 without the remote control and for $50.00 extra you can have get a remote control. The case is the traditional black heavy duty case Audio GD uses in most of their products. It also has an 80 step volume control which Audio Gd describes on their web page in detail. For the price it would be difficult to find products built like the NFB6 with all the features described. Audio GD is packed with features unheard of in this price range.
The NFB6 has two gain modes designed into the unit. The low setting is set at 0 db and high has gain of 9db and my auditioning was done primarily using the low setting as I found the high setting very hard and aggressive and edgy to a point where I always wanted to stop listening. Single ended mode which most users in this price range would be using the amplifier is hard and grainy most of the time with a single ended source and is better in all ways and a significant step up in balanced mode. Single ended most $250.00 amplifiers and many even less priced would be a better option. The full description of all the power ratings are listed on the website and power for any headphone will not be an issue. The unit is fully discrete design with no opamps and all quality parts. I had to keep reminding myself to review this amp I also had to consider its price point and that all my other headphone amplifiers are two or three times more expensive than the NFB6
The NFB6 sounds better in balanced mode. It drives the HD800 and the HE500 very easily. It is clean and neutral. It had pretty much all balanced flavor to the bass and midrange. The treble at first was brittle but it did get better used balanced and with some hours on the unit. Most of my time using the NFB6 has been with the HD800 using a Norse balanced cable provided by Trevor for this review. The cable is outstanding and really provided a clear window into the music and allowed me to evaluate this amplifier and hear both the amplifiers strength and also to hear what the amplifier did not do as well. I have also struggled to write this review as my time with the NFB6 has been a mixed bag of ups and downs. I think most users using this amplifier would be using the orthodynamic headphones offered by HiFiman and for those headphones this would be a nice low cost alternative
The NFB6 in balanced mode is clean. It is also very neutral. Soundstage is excellent. It is both deep and wide. There is no noise as the amplifier is very quiet. Bass is not tipped. It goes deep but does not hit hard. Treble is as it should be balanced and is brittle single ended. The amplifier is not as dynamic as others I have heard in this price range and some priced less. High gain makes it hard and aggressive low gain requires the amplifier to be listened to at higher volume settings but it also the best way I found to use the NFB6. Single ended was and is too hard and edgy. Most of all it is very fatiguing and balanced is really where this amplifier is best suited to play music. The NFB6 does not favor any genre all are played equally. Vocals are clean and not sibilant. Instrument tone is good.
As most can see this has been a very difficult review for me to do. The NFB6 has been a very mixed bag over the last four weeks. It is a $400.00 amplifier built well and loaded with features. It also need to be used balanced which for many will make this a harder choice as headphone and sources can get expensive. In single ended mode this amplifier is outclassed by lower priced amps. In this price range there are not too many balanced amplifiers. I would only recommend this amplifier for balanced use and in that context it is a three star performer. It is good solid well built amplifier by a manufacturer known for building battleship products. I can see this being used by people as a stop gap owning expensive headphones that want to experience balanced but cannot yet afford a reference amplifier. It does not excite as the much more expensive amps I have. It is also not the last word in detail or extension. I also recommend this for the users of the HE500 as it has gobs of power and it can be used to power the orthodynamic headphoneseasily. To sum it all up it’s a very clean and quiet headphone amplifier that will please many and can be a good stepping stone for people who want to build a balanced system and to be used as a stepping stone for the HD800 until you funds for the more expensive audio gd balanced amps or other amplifiers on the market. A good value based on price and recommended only for balanced use.