Audio-GD NFB-28.28 Balanced DAC/Preamp/Headphone amp (ES9028PRO)

    Audio-GD NFB-28.28 Balanced DAC/Preamp/Headphone amp (ES9028PRO)

    RM 3,471.70

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    Product ID : 206935590 Brand : Audio-GD Model / SKU : NFB-28.28 Conditions : New

    Audio-GD NFB-28.28 Balanced DAC/Preamp/Headphone amp (ES9028PRO)

    Hai Wei
    ** Facebook http://m.me/StarsPickerAudio
    ** WhatsApp https://goo.gl/GsPFak

    NFB-28.28 (ES9028Pro)

    Discrete DAC+ Headphone amplifier / Preamplifier
    With XLR / RCA analog inputs
    DSD , DXD support from USB & I2S Input
    32bit / 768K Sabre ES9038Pro
    32bit / 384K Asynchronous Transfer Xmos U208
    Built in OCC

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

    Amanero combo 384 Intruduce and driver download
    Xmos U208 Introduce and drivers download

    Different between NFB-28.38 and NFB-28.28:
    The different is the NFB28.38 had built in ES9038 Pro, NFB28.28 had built in ES9028 pro, other parts are exact same. In sound quality, NFB28.38 had slightly better on transparency.

    Different to the NFB-29.38:
    The NFB-29 is a single ended DAC with headamp and preamp (+/- 30V DC high voltage power supply ), The NFB-28 is balance DAC with headamp and preamp (+/-15V DC power supply ). So They had same output power specs can drive most headphone as well.
    If customer like to keep your headphone with single ended connector (6.3MM), choice the NFB-29 get better performance than the NFB-28.
    If customer had the balance connector headphone or can modify the headphone with balance connector, choice the NFB-28.

    Fully balanced design built by discrete analog stages without any OPA and coupling caps in the signal channels, built in real balanced DAC. Output for headphone (4-pin XLR or 1/4") and DAC (fixed output) with preamp (variable output)
    Non- feedback ACSS analog output stage .
    Large R-core transformers and Hi-fi grade parts like DALE resistors, WIMA caps .
    Total of 6-group PSUs are used to purify the power supply , the analog amp has discrete PSU power supply
    Four-channel 100 steps digitally controlled relay-based volume control avoids channel imbalance and improves sound quality .
    Supper Exponential Volume Characteristic with Fast / slow selection, easy match the volume with very different sensitivity headphone / speaker .
    4 digital inputs: USB / Optical / Coaxial RCA / I2S
    2 analog inputs: XLR / RCA (The RCA input can conversion to XLR output native without extra convertor )
    DAC output: XLR / RCA / ACSS
    Headphone output : 4 pin XLR / 1/4" (6.3MM) SE
    User can change the digital parameter setting
    4 types gain modes , drive the high and low sensitivity headphones as easy .

    Modification guide on headphone jack for 4-pin balanced headphone output.
    Click here to read: modification guide


    Detail of the Current Conveyor (ACSS) Technology

    Impedance matching:
    The NFB-28 had one group analogy RCA and one group analogy XLR inputs ,can connect external DACs , working as a decent headphone amp .There are a lot different DACs in worth, they had different design and output impedance . For avoid the sound quality effect by different DAC's output impedance, in the NFB-28, it had design 4 groups expensive class A FET buffers in the input . All the analogy input signals through these FET buffers, the output impedance had become very low, even the source had high or low output impedance.
    The FET buffers working on pure class A state, and it is so short signal journey , it can keep the sound quality without coloration ,dry and harsh .

    Simple and short signal transfer is best:
    The NFB-28 applies the newest ESS high-end Sabre32 DA chip ES9038Pro which can support up to 32Bit/384KHz input .
    ES9038Pro in voltage output model , there is -12DB THD+N worst , to be achieve the best performance of ES9038Pro , must work in current output model .
    In some other ES9038Pro built in DAC design , ES9038Pro output signal have to through 3 step OPAs implement analogy signal process .
    The NFB-28 had different design , applies Non-feedback ACSS design. The ES9038Pro feed to the ACSS circuit by balanced model without any OPAs .
    The ACSS circuit naturally working in current model and have design difference current input , it can transfer the ES9038Pro current signal to output and implement the I/V conversion in current model in one ACSS amp . And this ACSS amp only have one current gain stage , the ES9038Pro 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 ES9038Pro .
    So our ACSS design is the best combo with ES9038Pro achieve the best performance .
    Upside in the picture is the standard ES9038Pro headphone amp design. The bottom is the NFB-28 design .

    Super low THD (Test by AP SYS-2722,0DBV output level) Flat frequency response (Test by AP SYS-2722)

    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 ES9038Pro .

    Strong diamond difference output stages:
    The NFB-28 had design 4 groups diamond difference output stages as the balance output drive stages, every parts had exact matching before assemble so don't need any human adjustment .

    The output stages had built in 4 pair 15W transistors for offer strong drive ability , the balance output mode had 4X times power than the same state single-ended mode, so no matter drive the high and low sensitivity headphones . The diamond different design can avoid switch distortion , it working as the class A but don't want large idle current . The balance drive mode can kill the noise and distortion in the end of the headphone, much improve the sound stage, background and the transparency ,ect.

    Multi-ply power supplies are the key of sound :

    NFB-28 applies the excellent DA chip ES9038Pro 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-28 uses A total of 6 groups PSU power supply for all digital and analog circuits.
    To achieve high S/N, the control circuit is powered with separate regulator.

    Strong power supply.

    The I/V conversion volume control without sound degradation:

    Usually the volume control can be implemented in the DAC + amplifier combo in two methods
    Method 1: The volume control is implemented into the digital stage. The major drawback is that 1 bit of the D/A conversion is lost in every 6DB volume reduction. So, even though the built-in DA chip is 32 bit, in fact, only 16 bit may be left at low volume level.
    Method 2: The volume control is implemented in the analog amplifier input stage through a volume pot to reduce the signal level. However, the volume pot affects the sound quality adversely. A low grade volume pot loses the details and creates channels imbalance resulting into soundstage distortion. Even a high grade volume pot inevitably loses the details. Both methods degrade the sound quality.
    The NFB-28 applies the I/V conversion volume control, the volume control is just a variable passive I/V conversion being placed at the ACSS amplifier output, where the output is current signal but not voltage signal. I/V conversion is to change the volume level from the current (I) signal to the voltage (V) signal. (Like R-2R D/A chips output passive I/V conversion) It can keep the signal frequency band flat while not losing any detail. It does not degrade the sound quality in every volume level. In front of the volume control, there are four groups of diamond non-feedback buffer output stages that offer very low output impedance.
    NFB-28 applies digitally controlled relay-based volume control in 100 steps. It has 90DB control range ( most other volume control only had around 70DB range, so the device want to design the gain switches ) allow users to control the volume level smoothly. NFB-28 has two relay-based volume control channels through changing the DALE resistors to control the volume to avoid channel imbalance, achieving the best performance and sound quality of the gear. While change the volume, the combine relays break or close, it may had slightly switch sound on output and disappear while stop change the volume.

    Precise digitally controlled relay-based volume control. Fast / Slow two volume control characteristic


    The NFB-28 had built in Multi-ply shield boards, to separate the transformer, power supply, digital parts and analogy parts for avoid the different parts had disturb . Even though the power input IEC socket, it had hide in a copper shield box .

    Uses all Hi-end grade components, including DALE resistors, WIMA caps, custom order NOVER (UK brand) caps, Neutrik headphone output socket, ect .

    Discontinued the analog idle input short circuit function:
    The unit had design the analog idle input short circuit (In 5 and In 6) for avoid the disturb between different sources.
    This design also applied in a lot high end
    brand devices.
    The working theory :
    Without the idle input short circuit ,if the input 5 and input 6 had connect two extra DACs, while users select the either input 5 and input 6 , the another input signal will fire through the circuits and mix into the using signal, even though this signal is weak but still can degrade on the sound quality.
    With the idle input short circuit function : if user select either the input 5 and input 6, the another input signal will short circuit then no any signal fire through circuits , can keep the sound quality had not degrade.
    Below case users want to discontinued the idle input short circuit function, pull off the 4 jumpers as mark on the photo:
    1, The same extra source not only connect the
    unit analog input, but connect with other amps simultaneity.
    2, The same extra source connect to the
    unit input 6 and input 5 at simultaneity.

    I2S-RJ45 input format:
    ( 3.3V level , we can't guarantee the I2S input can cooperate with all I2S output devices.
    ( The I2S transmit want to take care the transmit cable )

    Pin 1 : SDATA
    Pin 3 : LRCK
    Pin 5 : SCLK
    Pin 7 : MCLK
    Pin 2,4,6,8 GND
    Customer can custom order the different define of the I2S pins free .

    Please note: Don't hot push / pull of the I2S cable. Any time must power off the units then push or pull the I2S cable.


    Gain button:
    Select the Fast / Slow volume control characteristics.
    H: Fast. 64 steps range.
    L: Slow. 100 steps range.
    F: (Full ) High gain mode.
    100 steps range. (For the low sensitivity headphone like the HE-6 or the source had low output voltage level)
    S: (Super)High gain mode. 64 steps range. (For the low sensitivity headphone like the HE-6 or the source had low output voltage level)

    The button on rear : Pull out for the DAC / preamp without volume control , Push into for the DAC / Preamp with volume control. The headphone output always had the volume control. Please operate the button while the unit power off .

    The display auto dark : Push into the jumper is auto dark .Please operate the jumper while the unit power off .

    DSD / PCM support from I2S input :
    The DSD/PCM support not only from the USB input, but the I2S input. The NFB-28 can detect the I2S input signal, if input DSD signal, it will auto to remove the DSD pop noise while select the DSD track .

    Digital filter setting:
    IIR0 与IIR1:For DSD.
      IIR0 IIR1
    47K Push Into Push Into
    50K Pull Off Pull Off
    60K Pull Off Push Into
    70K Push Into Pull Off
    FIR0,FIR1,FIR2: For PCM.
      FIR_0 FIR_1 FIR_2
    Fast roll-off, Linear: Push Into Push Into Push Into
    Slow roll-off, Linear: Push Into Push Into Pull Off
    Fast roll-off, Minimum: Push Into Pull Off Push Into
    Slow roll-off, Minimum: Push Into Pull Off Pull Off
    Fast roll-off, Apodizing: Pull Off Push Into Push Into
    Fast roll-off, Hybrid: Pull Off Pull Off Push Into
    Brickwall filter: Pull Off Pull Off Pull Off

    Specifications might subject to change without prior notice for product improvement.

    S/N Ratio


    <0.0008% (2.8V output level )


    Output impedance

    2 ohm

    Output Level

    Headphone output : 19V RMS (balanced , max)
    Preamp Variable output (balanced) : 10V RMS (max)
    Preamp Variable output (RCA) : 5V RMS (max)
    ACSS: 2MA+2MA

    Headphone amp output power level
    (Only for headphone.)
    Balanced mode

    9500mW / 25 ohm
    8000MW / 40 ohm
    3500MW / 100 ohm
    1200MW / 300 ohm
    600MW / 600 ohm

    Headphone amp output power level
    (Only for headphone.)
    Single ended mode

    3600mW / 25 ohm
    2500mW / 40 ohm
    1100mW / 100 ohm
    400mW / 300 ohm
    200mW / 600 ohm

    Digital Input Sensitivity

    0.5 Vp-p(75 Ohms, Coaxial)
    19 dBm (Optical)

    Analog Input Sensitivity
    0.7V to 5V RMS (RCA)
    0.7V to 10V RMS (XLR)


    Frequency Response (DAC +AMP)

    20Hz - 20KHz (<-0DB)

    Support Operate Systems (USB)

    Windows, Mac

    Support Sampling

    USB / I2S model: 44.1kHz, 48kHz, 88.2kHz, 96kHz, 176.4kHz , 192kHz, 352.8kHz,384kHz
    Coaxial model: 44.1kHz, 48kHz, 88.2kHz, 96kHz, 176.4kHz ,192kHz
    Optical model: 44.1kHz, 48kHz, 88.2kHz, 96kHz

    Power Requirement

    Version 1: 100-120V AC 50/60 Hz
    Version 2: 220-240V AC 50/60 Hz

    Power Consumption


    Package Weight

    Approximately 5KG


    Approximately W240 X L360 X H80 (MM, Fully aluminium )


    AC power cord X1
    USB cable X1

    Custom Options:

    1, Upgrade to the Amanero combo384 USB module :
    2, Upgrade TCXO for ES9028Pro or ES9038 Pro for slight improve on the sound transparency .
    3, Custom order two pair RCA outputs replace ACSS outputs:
    4, Custom order HDMI replace RJ45 I2S input. 

    Last Updated @ 8/6/2017 12:18:27 PM

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