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 means Non-Feedback.
The NFB-5 applies the newest
high-end dual WM8741 which can support up to 24Bit/192KHz input. Similar to other WM8741 designs, the NFB-5 applies
Non-feedback ACSS output stage. The dual WM8741 feed to the ACSS output
stage without any OPAs so it can achieve very neutral sound quality.
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.
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.
The 32/192 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
Discrete ACSS headphone amp.
NFB-5 applies the excellent
dual 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.
uses 8 groups of high-quality PSU
with dedicated DC
supply. Digital and analog voltages each have separately isolated
internal power regulations.
analog power supply is more important for sound reproduce, in NFB-5,
the +15V and -15V for the ACSS analog output stages are high speed
Discrete PSU. They can offer pure and quick power supply for driving
the headphone exactly. The high voltage power supply can drive most
headphone from 15 to 600 ohms as well.
Strong power supply. 8 groups high performance PSU built in.
About volume in ACSS circuits:
For a headphone amp, the volume control is very
NFB-5 uses ACSS technology, which is very
different from conventional technology.
control is is placed at the ACSS modules output, where the output is the current signal, not the
voltage signal. The volume control is I/V conversion, and the volume
depends on the current (I) conversion to the voltage (V). (Like D/A
chips output I/V conversion)
As you can see, ACSS circuits have no
gain, as it is a completely different circuit.
The sound quality benefits from I/V
conversion volume control. Mark Levinson also knows that current
volume control has great benefits, so in their Top End preamp NO.32
volume control, they use many components to change the signal to
current signal (I), then through the R-2R network to control the
volume, and then change back to voltage signal (V) again. But NFB-5 is simply a more complete work in terms of the current signal,
and technically, it is superior to conventional technology.