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NFB-27(Version 2014 )(DSD / DXD )(Since 1st May 2014)
Fully Discrete  DAC+ Head amp / Preamplifier

DSD , DXD support from USB
32bit / 384K Sabre ES9018
32bit / 384K Asynchronous Transfer  USB-32 Chip
5 groups digital & 3 groups analogy inputs

OCC
wires and TCXOs built in


                  

              
Summarize Use Manual Specs Technology Detail Custom Option Shipping Cost

Detail of the Current Conveyor (ACSS) Technology

 
About NFB?

    
The NFB-27 applies the newest ESS high-end Sabre32 DA chip ES9018 which can support up to 32Bit/384KHz input .
       
To be achieve  the best performance of ES9018 , must work in current output model,  in voltage output model, there is -12DB THD+N worst .
       The standard current model  design usually need 3 amps (OPA) , the first amp implement I/V conversion, conversion the ES9018 output current signal to voltage signal .
       The second amp is the difference amp, conversion the balance signal to single-ended signal and implement the low pass analog filter , then through  volume control  feed to the third amp, the headphone amp or preamp .
       Every amp in the standard design usually have two gain stages built in, so  the ES9018 signal must through total 6 gain stages arrive the output stages .
       The NFB-27 applies Non-feedback ACSS design. The ES9018 feed to the ACSS circuit without any OPAs .
       The ACSS circuit naturally working in current model and have design difference current input , it can process the I/V conversion, signal difference and headphone amp in current model in one ACSS amp . And this ACSS amp only have one current gain stage , the ES9018 output signal only through one gain 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 ES9018 , users will know why the ES9018 had become popular in short time after release .
       So the ACSS design is the best combo with ES9018 achieve the best performance .
                                          Upside in the picture is the standard ES9018 headphone amp design. The bottom is the NFB-27 design .
 Click image to enlarge.        


        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 ES9018 .
                         

        

Power supply:
         NFB-27 applies the excellent ES9018 with  excellent analog output amps, 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-27 uses 11 groups of high-quality class A parallel connection PSU , which can offer very clear DC power for the DAC and amps, producing a very black background and neutral sound characteristic. The class A  PSU is very important for digital parts. Some designs may have very low jitter in theory, but if the power is supplied by a dirty or low-speed power supply, it will increase the jitter and pollute the data, and degrade the sound quality obviously.
        The class A parallel connection PSU has very high input impedance to avoid pulse through the PSU from affecting the DAC and low output impedance with very fast speed and high linearity, so it is a very clean power supply. In my experience, its sound is better than battery power supply, better human sound and neutral.
        The NFB-27 uses three high performance transformers. More than 50,000uf audio grade NOVER capacitors are used to ensure ample and smooth power feed. A total of 11 groups class A SPUs and 2 groups linear PSUs are used to purify the power supply. To achieve high S/N, the control circuit is powered with separate regulator.

      

Volume control:

           The volume control is also different from conventional technology. Conventional volume control technology is the volume control implement in the analog amp input stage through a volume pot to reduce the signal  . The volume pots quality effect the sound quality direct , the low quality volume pot cause lost the detail and channels imbalance cause the soundstage distortion  . Even the high performance volume pot still cause the detail lose. Whatever quality volume pots, must cause the S/N worst .
   
       But in the NFB-27 , we applied the I/V conversion volume control , the volume control just  a variable passive I/V conversion place at the ACSS amp 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 R-2R D/A chips output passive I/V conversion)  It can keep the signal frequency band flat and not lost any detail.
It can't degrade on sound quality in every volume level . After the volume , there are four groups  diamond non-feedback buffer output stages offer the very low output impedance  .
            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 implement the volume control , and then change back to voltage signal (V) again. But NFB-27 is simply a more complete work in terms of the current signal, and technically, it is superior to conventional technology. The less conversion bring much neutral sound .
            The volume control quality is much important in the real balance gear . It must guarantee the four channels signal control exact to achieve the performance of the real balance gear .  If the cool and hot of the balance signal can't guarantee exact, the balance output will has large distortion cause the sound quality and performance even much worst than a single end gear waste the  balance gear  design and the cost.
            In NFB-27 is applied a four channels digital control relays based volume control. .NFB-27 has total four channels through changing the DALE resistors to control the volume for avoid channels imbalanced ,achieve the best performance and sound quality of the gear.
           NFB-27 have 100 steps volume control, control range achieve 90DB (usually the steps volume ports, potentiometer volume port, relays base volume control all have around 70DB range  ), very smooth control range on first 50 steps , cooperate with 13DB high gain, so can very easy adjust the volume for  both high / low sensitivity headphone and speakers. While users change the volume, the different relays break or close, it may had slightly switch sound on output and disappear while stop change the volume.
             
NFB-27 Supper Exponential volume characteristic      The Volume steps comparison to normal volume knob       
                                                                                                      
Shield: 
         NFB-27 has complete separation of left, right amplifier channels, power supply, and transformer.
         NFB-27 uses heavyweight all-aluminum alloy chassis to prevent the eddy current of transformers from interfering on circuit board. 
         NFB-27 applies optical couple isolation for the MCU and the control implementations to prevent the MCU affecting the audio parts.

Static storage mode control software:
          In most control softwares design, the MCU will continuously output data to the perform parts , the MCU had the very high speed, so the output data become high frequency impulses disturb the audio signal circuits make the sound worst .  This product had applied static storage mode control software  , the MCU output once control data and save in the perform parts while just power on and users operate  ,then stop output data until users next operation. This design make the sound quality improve on the clear and transparency .


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