(Audio-gd Current Signal System) technology is Audio-gd's signature
technology for transmitting audio signals in the current domain.
This concept, first seen in 1966, has been adapted by us for many
years. Since 2005, we have been evolving this technology to include
it into all audio signal transmissions in our systems from digital
source to power amplifier. Since 2006, ACSS technology became Audio-gd's
signature technology and gains a lot of popularity.
The NFB-15 applies the newest high-end dual WM8741 which can support up to 32Bit/192KHz input .
The standard current model design
usually need 3 amps (OPA) ,
the first amp is the difference amp , conversion the 4
channels output signal from WM8741, become a single ended signal .
The second amp implement
the low pass analog filter , then through volume control feed to the third amp, the headphone amp
Every amp usually have two gain stages
built in so the WM8741 signal must through
total 6 gain stages arrive the output stages .
NFB-15 applies Non-feedback ACSS design. The WM8741 feed to the ACSS
circuit without any OPAs .
The ACSS circuit conversion, signal difference and headphone amp in current
model in one ACSS amp . And this ACSS amp only have one current gain
the WM8741 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 WM8741 .
So our ACSS design is the best combo with
WM8741 achieve the best performance .
Upside in the picture is the standard WM8741 headphone amp design.
The bottom is the NFB-15 design .
The ACSS also 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. 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 dual WM8741 .
Discrete ACSS headphone amp.
NFB-15 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 6 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-15,
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.
About volume in ACSS circuits:
For a headphone amp, the volume control is very
NFB-15 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-15 is simply a more complete work in terms of the current signal,
and technically, it is superior to conventional technology.