Audio-gd products had design and test based on the AP SYS-2722 (The top-drawer professional equipment in world)

Since 4th. April 2018,   the model had upgrade the volume ports:
The upgraded volume ports had built with Vishay or KOA resistors with dual resistors parallel ,  tolerance low to 0.05% .

Different to the C-2 ( 11th Anniversary Edition ):

          The C-2 is a single ended head amp and preamp (+/- 30V DC high voltage power supply ), The NFB-1AMP is balance head amp and preamp (+/-15V DC power supply ). So They had same output power specs and can drive most headphone very well.

          If customer like to keep your headphone with single ended connector (6.3MM), choice would be C-2 you get better performance than the NFB-1AMP.

           If customer have balanced connector headphone or can modify the headphone with balance connector, choice would the NFB-1AMP.


Summarize
Fully balanced class A design built by discrete analog stages without any OPA or coupling caps in the signal channels.

Non- feedback ACSS analog output stage.

8000mW at 40 ohm output, 16DB gain can drive the low sensitivity headphone very well.

Class A PSU's for DC supply.

Uses most Hi-end grade parts and exactly matched transistors, OCC wires.

Four-channel 100 steps digitally controlled relay-based volume control avoids channel imbalance and improves sound quality .

Supper Exponential Volume Characteristic, easy match the volume with very high headphone / speaker without change the gain mode.

5 groups input: RCA X2, XLR X2, ACSS X1

Preamp output : XLR / RCA / ACSS

Headphone amp output: 4pins XLR X1 / 6.3MM X1

　

Technology detail

Detail of the Current Conveyor (ACSS) Technology

Impedance matching:
              There are a lot different quality DACs. They have different design and output impedance . To avoid negative effect on sound quality by differences in DAC's output impedance, in the NFB-1 we have design a pair single-ended class A FET buffers in the input . All the RCA input signals go through these FET buffers, the output impedance become very low, even if the source have high or low output impedance.
        
              The FET buffers working in pure class A , and it has a short signal journey. this way we can keep the sound quality without colouration ,(dry and harsh) .
             

Core:
             NFB-1AMP have the same ACSS design with our top grade model Master 9 . It is a pure class A design built by discrete analog stages without any OPA or coupling caps in the signal channels.

              They seem complex , but in fact they are the most simple design the world has ever had .The simplest and shortest signal journey brings out the most neutral and least coloured sound.

              The ACSS is a non-feedback technology made with 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 ears. Here is a conflict of the classic circuits.
  
              But the ACSS opens a new field, it can offer a least colouration to the sound which is more neutral with very low distortion and high linearity. So it can retain the dynamics, detail and neutral sound (not bright or harsh.)
 
              All signal gain is in current mode all transistors work in class A mode.
The NFB-1AMP has all components exactly matched before installation.

                        Super low THD                                                 Flat frequency response
                                                                 

Strong class A output stages:
             The NFB-1AMP has in its design a pare of diamond differential output stages, every parts have been exactly matched before assembly .

              The output stages had four pair 15W transistors ,they also work in class A . (Drive most headphones)

             

Power supply:    

           The class A parallel connection PSU has very high input impedance to avoid pulse through the PSU from affecting the preamp and low output impedance with very fast speed and high linear, so it is a very clean power supply.

           The NFB-1AMP applies separate linear PSUs for the display and control parts, to avoid noise going through power line and affecting the amplifier.
           

Volume control:
           The volume control is also different from conventional technology. Conventional volume control technology is the volume control implemented in the analog amp input stage through a volume pot to reduce the signal . The volume pot will affect quality of the sound directly , The low quality volume pot can cause loss of the detail and cause channel imbalances . Even the high performance volume pot still cause the detail loss. Whatever quality volume pots, will still cause the S/N being adversely affected .

            But in the NFB-1AMP , 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 loose any detail. It want degrade sound quality at any volume level . After the volume , there are four groups diamond non-feedback buffer output stages with 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-1AMP 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 .

              In NFB-1AMP is applied a digital control relays based volume control. .NFB-1AMP has total four channels through changing the DALE resistors to control the volume avoid channels imbalances and achieve the best performance and sound quality.

               NFB-1AMP have 100 steps volume control, which offers very smooth control for both high / low sensitivity headphone and speakers. While users change the volume, the combine relays break or close, it may had slightly switch sound on output and disappear when you stop changeing the volume.
              NFB-1AMP Supper two sets Exponential volume characteristic  
                                                   

Shield:
               The NFB-1 design has no compromises , it's built fully with aluminium , the transformer interference can't travel through the aluminium chassis and be transferred to the analog amps, and there are two shielded boards to insulate the transformer and the power supplies.
          

Components:
              Uses all Hi-end grade components, including DALE resistors, WIMA caps, custom order NOVER (UK brand)  caps.