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NFB-11(2015 )(Since 1th Feb 2015)

Discrete  DAC+ Headphone amplifier / Preamplifier
DSD , DXD support from USB
32bit / 384K Sabre ES9018
32bit / 384K Asynchronous Transfer  USB-32 Chip


        

                
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About ACSS:
         ACSS (Audio-gd Current Signal System) is Audio-gd's system for transmitting audio signals in the current domain. This concept, first seen in 1966, we have used for many years, and since 2006, have evolved the technology to include all audio signals in our systems from the digital source to the power amplifier. Since 2005, ACSS comp5nts have become Audio-gd's most popular products.


 
About NFB?

    
The NFB-11 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 .
       Every amp usually have two gain stages built in so  the ES9018 signal must through total 6 gain stages arrive the output stages .
       The NFB-11 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 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 .
       So our 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-11 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 .
                         
                                            Fully
Discrete ACSS headphone amp.
 
Click image to enlarge.                       

        

        NFB-11 applies the excellent DA chip ES9018 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 average 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 , but with plenteous dedicated DC supply circuits.
         The NFB-11 uses 6 groups of high-quality  PSU with dedicated DC supply. Digital and analog voltages each have separately isolated internal power regulations.
         This massive power supplies design usually only applied in the USD1000+ products .
         The analog power supply is more important for sound reproduce, in NFB-11, the +15V and -15V for the  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.
 Click image to enlarge.            

 

About volume in ACSS circuits:
         For a headphone amp, the volume control is very important.
         In ACSS, it 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-11 is simply a more complete work in terms of the current signal, and technically, it is superior to conventional technology.


                                                     ALPS 27 volume pot     
           1 % tolerance resistors and exact match transistors
  
Click image to enlarge.                       


 

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