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New figure :
1,   2X / 4X / 8X digital filter oversampling users setting by hardware .
What's advantage of setting the digital filter characteristic:
Except the NOS DACs , all DACs have applied the digital filter, the digital filter characteristic effects the sound quality and flavors. Most DACs have the fixed digital filter characteristic maybe not the best taste for the users. The NFB-10WM have 3 types  digital filter characteristic for users find the best sound of personal sense.

NFB-10WM
Dual WM8741 inside
Fully Balanced Dedicated DAC +  Fully Balanced HP/Pre amp

Dedicated DAC with RCA / XLR / ACSS output with variable and fixed line level
24Bit / 96KHz USB input and
24Bit / 192KHz Coaxial/Opitcal support
Applies ACSS


Price: Version A : USD780
Weight: Approximately 9.5kg
Dimension:  W240 X L360 X H83 (MM)
Accessories: Stock power cable X1,USB cableX1, optical cable X1

Summarize: Fully discrete amp without any OPA , couple caps ,non- feedback analog output stage and strong power supplys .
        The NFB-10WM uses 80W high performance transformers. More than 23,000uf audio grade NOVER capacitors are used to ensure ample and smooth power feed. The NOVER capacitors are specially custom order from NOVER (U.K.) according to Audio GD's requirements. Total of 7 PSU groups are used to purify the power supply. To achieve Silent operation, the control circuit is powered with separate regulator.
        The NFB-10WM uses high grade DALE resistors (1% tolerance) and WIMA caps, which offers a very neutral sound. RCA sockets are custom ordered and 24k gold-plated, XLR output sockets and headphone output sockets are Neutrik. All transistors are exact-matched Toshiba and Hitachi.
        The NFB-10WM applies the A-D (analog to digital) type relay-based volume control to avoid channel imbalance and improve on sound quality .


Sound Characteristics:  "Neutral but smoothness sounding ,it doesn't sound skeletal or digital (or metallic). There's meat aplenty on them bones . It's a sigma-delta DAC chip implementation without the dryness, neutrality without the emotional disconnection" - John Darko

Note: The S/PDIF interface default applied WM8805 (192KHz support), if you want replace the  DIR9001 (96KHz support) by free ,tell us  while place the order please.

What's different between these popular chips
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ก@ Dual WM8741 ES9018 AD1955 AD1852 WM8740
SNR 128 DB (Mono) 120 DB 120DB 114DB 117DB
DYNAMIC RANGE 128 DB (Mono) 129 DB 120DB 114DB 117DB

                                         
                             
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Please note:
All audio-gd products have change to new ACSS sockets as below ( expect the Master series ) , some photos maybe not update yet.

            

Illustrations on how to modify the headphone so that it can be connected to the NFB-10WM 4 pins HP amp output.
  
Click here to read:   modification

The parts of the headphone modification price is USD30, (includes one female 4 Pins plug and one male 4 Pins plug, some tapes and some WBT tin solder.)


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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.

Oversampling setting :            

Please note:
     Please shut down the NFB-10 and pull off the power cable then make the setting change.

Push into the jumpers between 192 and 96 : 2X oversampling , Linear phase 'brickwall' filter. Up to 192KHz support. 
    
Pull off the jumpers  : : 4X oversampling , Linear phase 'brickwall' filter. Up to 96KHz support.   
    
Push into the jumpers between 96 and 48 : 8X oversampling , Linear phase half-band filter for backward compatibility.
Up to 48KHz support.      
                                  
   
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About NFB?
      
NFB means Non-Feedback.
        The NFB-10WM version applies the newest  high-end dual WM8741 which can support up to 24Bit/192KHz input (Coaxial and optical input support up to 192KHz , USB support up to 96KHz/24bit). Similar to other WM8741 designs, Our NFB-10WM version applies Non-feedback ACSS output stage. The dual WM8741 feed to the ACSS output stage without any OPAs so it can achieve very neutral sound quality.
        The ACSS 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.
        The 24/96 USB interface outputs a I2S signal to dual WM8741.
        Applied the WM8805 as the SPDIF interface , its sound characteristic is same with the WM8741 which is detail but smooth, and it can support up to 192KHz input.  The WM8805 had quite low jitter (50PS),much less than the CS8416 ( 200PS ).
        Real fully balanced discrete design.
        Fully
Discrete ACSS headphone amp.
                       
   

       NFB-10WM 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-10WM uses 7 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-10WM, 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.

     NFB-10WM use ACSS technology, which is very different from conventional technology.
    In conventional technology the gain is fixed, like 3DB or 6DB.

        But in ACSS technology the gain changes with volume, and when you turn off the volume, the gain is -80DB or -100DB (in conventional technology it can't work lower than 0DB).
        While you are listening in normal volume, the gain may be around -50DB, or between -80 to +12DB.
        The volume control is also different from conventional technology. Conventional technology volume control is placed in the input, and attenuates the signal.
        But 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-10WM is simply a more complete work in terms of the current signal, and technically, it is superior to conventional technology.

 About the A-D type relays based volume control:

        In NFB-10WM is applied an exact A-D (analog to digital) type relays based volume control. It has a built-in CPU to pick up the analog volume pot position, through a ADC change to digital signal for the CPU count and control two relays volume boards through changing the DALE resistors to control the volume.
        This A-D type relay-based volume control has 32 steps, and with the High/Low gain switch is just like a 64-stepe, wide-range volume pot which can suit most users requests.
        This A-D type relay-based volume control can avoid channel imbalance and sound better than normal volume pots.
        For long long life, we apply a ALPS 27 volume as the analog position volume pot.  
            ALPS 27 analog position volume pot         
Exact volume control board  
           
              

 The NFB-10WM Functions:
    Front plate:
    
Power switch: Power ON/OFF the NFB-10WM.
     Balance Headphones socket
: Output for balance headphones.
    
Gain switch: Select gain between low gain (+0DB) and high gain (+12DB).
    
Volume knob: Control the volume level of the headphone and variable DAC output.
     1/4' headphone socket : For single-ended headphones.
     Preamp button: Select the NFB-10WM output between
dedicated DAC output or headphone output ,the dedicated DAC output level can be chosen between variable and fixed .
    
Selector switch: Select source between USB, coaxial and optical.

     Rear:
     USB socket: For USB input.
     Opt socket: For optical input.
     Coax socket: For coaxial input.
     Line out sockets: For dedicated DAC output.
(The DAC output level can be chosen between variable and fixed , see below).

 How to set the NFB-10WM DAC output as variable line level only?

      
The NFB-10WM has dedicated DAC output for RCA ,XLR and ACSS.  In default its output level setting is at variable only (if yours amp or active speakers without volume control, we advice setting to variable output only). But owners can set it to can select between variable and fixed or output variable line level only . See the photos, pull off the jumper to set the DAC output to variable only.
     Please note, the ACSS output is only variable at fixed level mode. ( The NFB-10WM always working with ACSS in every modes, in variable output mode, the ACSS signal just separated between ACSS modules and the ACSS output sockets , so can't degrade on sound quality, just choice what mode you wanting . )
          
Setting the Fixed and variable output       

                                        

 If we only use the RCA or 1/4' headphone output, is the NFB-10WM wasted or not fully utilized?

           The NFB-10WM is a real balanced output DAC and headphone amp, it has balanced (ACSS, XLR and balanced headphone output), single-ended output (RCA and 1/4' headphone output). There are 4 ACSS modules in the NFB-10WM for balanced output, and all the ACSS modules have balanced input, so even through single-ended output, the WM8741 DA chips will perform fully.  

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Improvement may result in changes in specifications and
design without notice.
S/N Ratio
118DB
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 Output Level
 Headphone output : 21V RMS  (balance)
Variable output : 12V RMS (balance, volume max)
Fixed output: 5V RMS (balance)
Fixed output: 2.5V RMS (RCA)
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Output power
Only for headphone.

 4W  /  100 ohm
700mW  /  600 ohm

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Output impedance 2 ohm /  Headphone output
2 ohm / DAC output
Input Sensitivity
0.5 Vp-p(75 Ohms, Coaxial)
19 dBm (Optical)
USB1.1 ,USB2.0 (Full Speed)
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Frequency Breadth
20Hz - 20KHz
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Power Requirement
1 Version  100-120V  AC 50/60 Hz
2 Version  220-240V  AC 50/60 Hz
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Power Consumption
17W
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Transformer Power
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80W
Package Weight
Approximately 9.5KG
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Accessories
AC power cord            X1
USB cable                X1
Optical cable            X1
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Operating Temperatures
+5 ขXC to +40 ขXC
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Operating Humidity
5 % to 90 % (without dew)
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