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 2005, have evolved the technology to include all
audio signals in our systems from the digital source to the power
amplifier. Since 2006, ACSS comp5nts have become Audio-gd's most popular
NFB means Non-Feedback.
NFB-9.2 applies the
newest high-end dual WM8741 which can support up to
24Bit/192KHz input (AES , Coaxial and USB). Similar to other WM8741 designs, Our NFB-9.2 applies
Non-feedback ACSS output stage. The dual WM8741 feed to the ACSS output
stage without any OPAs so it can avoid sound coloration .
The ACSS is a non-feedback
technology made with fully discrete amplifiers. Most people know the
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.
design, the WM8741 feed to a difference voltage amp through voltage
signal . In NFB-9.2 , the dual WM8741 has feed to the ACSS parts direct through
balanced current signal . The current signal mode can bring the best
signal of the DA chips .
The output buffers are
Non-feedback. For low impedance, we applied the dual FET buffer output stage
which is quite less colored than most conventional circuits.
The two OPAs
in the NFB-9.2 just for DC serve to keep the output DC offset at zero ,
allow the DAC
analog parts are without couple
caps to avoid coloration.
The 24/192 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
NFB-9.2 applies the excellent dual DA chip 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.
three R-core transformers (135W total), one 35W R-core supplies
power for digital parts, another two 50W R-cores supplies power for
analogy parts. The power transformers and rectifiers are carefully
shielded from the electric field of the power transformers and
rectifiers' frequency transmission. More than 50,000uf
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 requirement.
The NFB-9.2 uses total 16 groups PSU . The 15 groups of high-quality class A parallel
connection PSU with dedicated DC supply double-stage PSU, which can
offer very clear DC power for the DAC ,
a very black background and neutral sound characteristic. The
double-stage PSU is very important for digital parts. Some designs
may have very low jitter in theory, but if the power is supplied by
a dirty or low-speed power supply, it will increase the jitter and
pollute the data, and degrade the sound quality obviously.
The class A parallel connection PSU has very high input
impedance to avoid pulse through the PSU from affecting the DAC and
low output impedance with very fast speed and high linearity, so it
is a very clean power supply. In my experience, its sound is better
than battery power supply, better human sound and neutral .
To achieve high
S/N, the control circuit is powered with
The massive all double stages PSU power supply.
Uses most Hi-end
Uses mostly DALE
and Vishay resistors, WIMA ,EVOX capacitors and a lot SOLEN caps.
The electrolyte capacitors are custom ordered from NOVER (a UK
brand), and exact-matched transistors. RCA sockets are custom
ordered and 24k gold-plated, the power socket is RA 24k gold-plated.
Neutrik balance sockets and Canare BNC socket .All transistors are
Toshiba and Hitachi.
If I only use the RCA output, is the NFB-9.2 wasted or not
The NFB-9.2 is a real balanced output DAC, it has XLR (balanced), RCA
(single-ended), and ACSS output. There are 4 ACSS amps in the NFB-9.2 for balanced
output, and balanced input, so even
through RCA output, the dual WM8741 DA chips will perform fully.