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NFB-15(Version 2014 )(Since 20th May 2014)

Discrete  DAC+ Headphone amplifier / Preamplifier
32bit / 384K Asynchronous Transfer  USB-32 Chip
Built in 2 Pieces Hi-end grade WM8741 Chips


Summarize Use Manual Specs Technology Detail Custom Option Shipping Cost

About ACSS technology:
         ACSS (Audio-gd Current Signal System) technology is Audio-gd's signature technology for transmitting audio signals in the current domain. This concept, first seen in 1966, has been adapted by us for many years. Since 2005, we have been evolving this technology to include it into all audio signal transmissions in our systems from digital source to power amplifier. Since 2006, ACSS technology became Audio-gd's signature technology and gains a lot of popularity.

About NFB?

The NFB-15 applies the newest  high-end dual WM8741 which can support up to 32Bit/192KHz input .
       The standard current model  design usually need 3 amps (OPA) , the first amp is the difference amp ,  conversion the 4 channels output signal from WM8741, become a single ended signal  .
       The second amp  implement the low pass analog filter , then through  volume control  feed to the third amp, the headphone amp .
       Every amp usually have two gain stages built in so  the WM8741 signal must through total 6 gain stages arrive the output stages .
       The NFB-15 applies Non-feedback ACSS design. The WM8741 feed to the ACSS circuit without any OPAs .
       The ACSS circuit conversion, signal difference and headphone amp in current model in one ACSS amp . And this ACSS amp only have one current gain stage , the WM8741 output signal only through one stage can arrive the output stages .
      The shortest signal journey can reproduce the best detail and dynamic, and almost without sound coloration , It can show the  real performance of the WM8741 .
       So our ACSS design is the best combo with WM8741 achieve the best performance .
                                          Upside in the picture is the standard WM8741 headphone amp design. The bottom is the NFB-15 design .

         The ACSS also is a non-feedback technology made with fully discrete amplifiers. Most people know the global feedback design can offer better specs in test measurements, and non-feedback can't do well in test measurements but can offer better sound for the human's ears. Here is a conflict of the classic circuits.
        But the ACSS opens a new field, it can offer a least coloration sound which is more neutral with very low distortion and high linearity. So it can retain the dynamics, detail and neutral sound but not sound bright or harsh.
        The output buffers are Non-feedback. For low impedance, we applied a diamond output stage which is quite less colored than most conventional circuits.
        The DAC is without couple caps to avoid coloration. There are two OPAs built in as the DC serve  to keep the DC offset .
        The 32bit / 384K USB interface outputs a I2S signal to dual WM8741 .
Discrete ACSS headphone amp.


         NFB-15 applies the excellent dual WM8741 and excellent analog output stages, but these are not the only keys of the best sound. The power supply is most important. Even applying the best DA chip and the best amp, if matched to a normal power supply, the total sound may still be average or sound musical but can't be neutral and detailed. That is why it is easy to find hi-end grade gears maybe without the best chips or amp stages, but with plenteous dedicated DC supply circuits.
         The NFB-15 uses 6 groups of high-quality PSU with dedicated DC supply. Digital and analog voltages each have separately isolated internal power regulations.
         The analog power supply is more important for sound reproduce, in NFB-15, the +15V and -15V for the ACSS analog output stages are high speed Discrete PSU. They can offer pure and quick power supply for driving the headphone exactly. The high voltage power supply can drive most headphone from 15 to 600 ohms as well.

        Strong power supply.

About volume in ACSS circuits:
For a headphone amp, the volume control is very important.
uses ACSS technology, which is very different from conventional technology.
            The volume control is  is placed at the ACSS modules output, where the output is the current signal, not the voltage signal. The volume control is I/V conversion, and the volume depends on the current (I) conversion to the voltage (V). (Like D/A chips output I/V conversion)
            As you can see, ACSS circuits have no gain, as it is a completely different circuit.
            The sound quality benefits from I/V conversion volume control. Mark Levinson also knows that current volume control has great benefits, so in their Top End preamp NO.32 volume control, they use many components to change the signal to current signal (I), then through the R-2R network to control the volume, and then change back to voltage signal (V) again. But NFB-15 is simply a more complete work in terms of the current signal, and technically, it is superior to conventional technology.



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