Audio-gd products had
design and test based on the AP SYS-2722 (The top-drawer
professional equipment in world)
Since 4th. April
2018, the model had upgrade the volume ports:
volume ports had built with Vishay or KOA resistors with dual
resistors parallel , tolerance low to 0.05% .
Different to the C-2 ( 11th Anniversary Edition ):
The C-2 is a single ended head amp and preamp (+/- 30V DC high
voltage power supply ), The NFB-1AMP is balance head amp and
preamp (+/-15V DC power supply ). So They had same output power
specs and can drive most headphone very well.
If customer like to keep
your headphone with single ended connector (6.3MM), choice would
be C-2 you get better performance than the NFB-1AMP.
If customer have
balanced connector headphone or can modify the headphone with
balance connector, choice would the NFB-1AMP.
Fully balanced class A design built by discrete analog stages
without any OPA or coupling caps in the signal channels.
Non- feedback ACSS analog output stage.
8000mW at 40 ohm output, 16DB gain can drive the low sensitivity
headphone very well.
Class A PSU's for DC supply.
Uses most Hi-end grade parts and exactly matched transistors,
Four-channel 100 steps digitally controlled relay-based volume
control avoids channel imbalance and improves sound quality .
Supper Exponential Volume Characteristic, easy match the volume
with very high headphone / speaker without change the gain mode.
5 groups input: RCA X2, XLR X2, ACSS X1
Preamp output : XLR / RCA / ACSS
Headphone amp output: 4pins XLR X1 / 6.3MM X1
Detail of the Current Conveyor (ACSS) Technology
There are a lot different quality DACs. They have different design
and output impedance . To avoid negative effect on sound quality by
differences in DAC's output impedance, in the NFB-1 we have design a
pair single-ended class A FET buffers in the input . All the RCA
input signals go through these FET buffers, the output impedance
become very low, even if the source have high or low output
The FET buffers working in pure class A , and it has a short signal
journey. this way we can keep the sound quality without colouration
,(dry and harsh) .
NFB-1AMP have the same ACSS design with our top grade model Master 9
. It is a pure class A design built by discrete analog stages
without any OPA or coupling caps in the signal channels.
They seem complex , but in fact they are the most simple design the
world has ever had .The simplest and shortest signal journey brings
out the most neutral and least coloured sound.
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 ears. Here is
a conflict of the classic circuits.
But the ACSS opens a new field, it can offer a least colouration to
the sound which is more neutral with very low distortion and high
linearity. So it can retain the dynamics, detail and neutral sound
(not bright or harsh.)
All signal gain is in current mode all transistors work in class A
The NFB-1AMP has all components exactly matched before installation.
Super low THD
Flat frequency response
Strong class A output stages:
The NFB-1AMP has in its design a pare of diamond differential output
stages, every parts have been exactly matched before assembly .
The output stages had four pair 15W transistors ,they also work in
class A . (Drive most headphones)
The class A parallel connection PSU has very high input impedance to
avoid pulse through the PSU from affecting the preamp and low output
impedance with very fast speed and high linear, so it is a very
clean power supply.
applies separate linear PSUs for the display and control parts, to
avoid noise going through power line and affecting the amplifier.
all Hi-end grade components, including DALE resistors, WIMA
caps, custom order NOVER (UK brand) caps.
The volume control is also different from conventional
technology. Conventional volume control technology is the volume
control implemented in the analog amp input stage through a
volume pot to reduce the signal . The volume pot will affect
quality of the sound directly , The low quality volume pot can
cause loss of the detail and cause channel imbalances . Even the
high performance volume pot still cause the detail loss.
Whatever quality volume pots, will still cause the S/N being
adversely affected .
But in the
NFB-1AMP , we applied the I/V conversion volume control , the
volume control just a variable passive I/V conversion place at
the ACSS amp 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 R-2R D/A chips output passive I/V conversion)
It can keep the signal frequency band flat and not loose any
detail. It want degrade sound quality at any volume level .
After the volume , there are four groups diamond non-feedback
buffer output stages with very low output impedance .
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 implement the volume control , and then change back to
voltage signal (V) again.
NFB-1AMP is simply a more complete work in terms of the current
signal, and technically, it is superior to conventional
technology. The less conversion bring much neutral sound .
In NFB-1AMP is applied a digital control relays based volume
control. .NFB-1AMP has total four channels through changing the
DALE resistors to control the volume avoid channels imbalances
and achieve the best performance and sound quality.
NFB-1AMP have 100 steps volume control, which offers very smooth
control for both high / low sensitivity headphone and speakers.
While users change the volume, the combine relays break or
close, it may had slightly switch sound on output and disappear
when you stop changeing the volume.
NFB-1AMP Supper two sets Exponential volume characteristic
The NFB-1 design has no compromises , it's built fully with
aluminium , the transformer interference can't travel through
the aluminium chassis and be transferred to the analog amps, and
there are two shielded boards to insulate the transformer and
the power supplies.