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 2006, have evolved the technology to include all
audio signals in our systems from the digital source to the power
amplifier. Since 2005, ACSS comp5nts have become Audio-gd's most popular
NFB mean Non-Feedback .
The NFB-2 applies two pcs newest
Wolfson high-end DA chip WM8741 which can support up to
32Bit/192KHz input. Compared to other WM8741 designs, Our NFB-2 applies
Non-feedback ACSS output stage for I/V conversion, and Non-feedback
power supply for the whole gear.
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.
The output buffers are
Non-feedback, for low impedance, we applied a two-stage parallel
connection, the output impedance is only 20 ohms.
The DAC is without couple
caps to avoid coloration.
The 24/96 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
(Note: While users want to replace the DIR
module, please power off the NFB-2 and pull off the power cable at
Click image to enlarge.
NFB-2 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
NFB-2 uses 6 groups of high-quality class A parallel connection PSU
with dedicated DC
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.
Left button: power ON/OFF switch.
The knob: Select built-in DAC
source between USB, coaxial and optical.
Right button: Choose between RCA and
ACSS output configure. (Owners can choose this button anytime.)
What's different between NFB-2 and NFB-3.1?
differences are as follow:
1, The NFB-3.1 applies 2 groups of
class A parallel connection PSU supplied for analog output stage,
(the analog output stage power supply is very important, so we keep
2 groups of
class A parallel connection PSU here). Another 5 groups of linear
PSU's supplied for other parts. The NFB-2 applies 6 groups class A
parallel connection PSU for the whole gear, and 1 linear PSU for
the control parts.
2, The NFB-3.1 applies
a toroidal transformer, the
NFB-2 applies an R-core transformer.
3, The NFB-3.1 applies mostly 1% SMD resistors and caps, the NFB-2 applies mostly
DALE resistors and WIMA
4, The NFB-3.1 have digital filter setting by software, the NFB-2 have
digital filter setting by hardware.