Audio-gd :: NFB-29H Single-end Discrete DAC+ Headphone amplifier / Preamplifier With 2x RCA / 32bit / 384K Sabre ES9018 / 32bit / 384K Asynchronous Transfer Amanero / DSD , DXD support from USB/ 2xTCXO / with remote control
Price: 932.34 EUR ( 758.00 EUR Net Price)
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Audio-gd NFB-29H

NFB-29H (Version 2016 )#

The single ended version based on NFB-28
  • Discrete DAC+ Headphone amplifier / Preamplifier
  • With 2 groups RCA analog inputs
  • DSD, DXD support from USB & I2S Input
  • 32bit / 384K Sabre ES9018
  • 32bit / 384K Asynchronous Transfer Xmos U8
  • OCC and hi-end parts applied


Main features

  • Multiply shield boards to isolation the power input socket, transformer, power supplies, digital part and the analog part.
  • Fully Discrete design built by discrete analog stages without any OPA and coupling caps in the signal channels, built in DAC, output for headphone (4-pin XLR or 1/4") and preamp output.
  • Non- feedback ACSS analog output stage.
  • The analogy amps working under +/- 30VDC for got the super well linear and offer high power output in single ended design.
  • 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.
  • Two-channel digitally controlled relay-based volume control to avoid channel imbalance and improve sound quality.
  • 4 digital inputs: USB / Optical / Coaxial RCA / I2S
  • 2 analog inputs: XLR / RCA
  • DAC output: RCA / RCA / ACSS (User can set either variable output level as preamp or fixed output level as dedicated DAC)
  • Headphone output : 4 pin XLR / 1/4" (6.3MM) SE
  • Static storage mode control software for avoid disturb sound quality, the MCU output once control data and save in the perform parts, then stop output data until users next operation.
  • Digital filter setting available.
  • 4 types gain modes, drive the high and low sensitivity headphones as easy.


Audio-gd NFB-29H

Impedance matching#

The NFB-29 had two groups analogy RCA 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-29, it had design a pair single-ended class A FET buffers in the input. All the analogy RCA 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-29 applies the newest ESS high-end Sabre32 DA chip ES9018 which can support up to 32Bit/384KHz input.
ES9018 in voltage output model, there is -12DB THD+N worst, to be achieve the best performance of ES9018, must work in current output model. In some other ES9018 built in DAC design, ES9018 output signal have to through 3 step OPAs implement analogy signal process.
The NFB-29 had different design, applies Non-feedback ACSS design. The ES9018 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 ES9018 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 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.

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 .



Audio-gd NFB-29H



Strong diamond difference output stages#

The NFB-29 had design 2 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 working under + / - 30V DC power supplied, built in two pair 15W transistors, for offer strong drive ability, 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.
Multiply power supplies are the key of sound:
NFB-29 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-29 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.

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-29 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-29 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-29 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.

Audio-gd NFB-29H

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.