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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 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
products.
About NFB?
NFB mean Non-Feedback .
The NFB-2(2014) applies two pcs newest
Wolfson high-end DA chip WM8741 which can support up to
24Bit/192KHz input ( Coaxial and USB). Compared to other WM8741 designs, Our
NFB-2(2014) applies
Non-feedback ACSS output stages .
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'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.
In most design, the WM8741 feed to a
difference voltage amp through voltage signal . In NFB-2(2014) , 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 output
impedance is only 10 ohms.
The two OPAs
in the NFB-2(2014) 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 32bit/ 192KHz 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
). Users can choice the DIR9001 module as the SPDIF interface instead
WM8805, the replace is so easy without solder , only pull off and push into .
(Note: While users
want to replace the DIR module, please power off the NFB-2(2014) and pull
off the power cable at first )
Fully discrete
design.
NFB-2(2014) applies the excellent 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.
The NFB-2 uses 6 groups of high-quality class A parallel connection PSU
with dedicated DC supply.
The class A parallel connection PSU has very
high input impedance for avoid pulse through the PSU from affecting the
DAC and low output impedance with very fast speed and high linear , so
it is a very clean power supply. In my experience, its sound is better
than battery power supply, better human sound and neutral.
Class A parallel connection PSU diagram
 
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Summarize
