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About NFB?
NFB means Non-Feedback.
The NFB-10WM version applies the
newest high-end dual WM8741 which can support up to
24Bit/192KHz input (Coaxial and optical input support up to 192KHz , USB support up to
96KHz/24bit). Similar to other WM8741 designs, Our NFB-10WM version 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
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 diamond output stage
which is quite less colored than most conventional circuits.
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
).
Real fully balanced discrete
design.
Fully
Discrete ACSS headphone amp.
 
NFB-10WM
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.
The
NFB-10WM
uses 7 groups of high-quality PSU
with dedicated DC
supply. Digital and analog voltages each have separately isolated
internal power regulations.
The
analog power supply is more important for sound reproduce, in NFB-10WM,
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 important.
NFB-10WM use ACSS technology, which is very
different from conventional technology.
In conventional technology the gain is fixed, like 3DB or 6DB.
But in ACSS
technology the gain changes with volume, and when you turn off the
volume, the gain is -80DB or -100DB (in conventional technology it
can't work lower than 0DB).
While you are listening in normal
volume, the gain may be around -50DB, or between -80 to +12DB.
The volume control is also
different from conventional technology. Conventional technology volume
control is placed in the input, and attenuates the signal.
But in ACSS, it 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-10WM is simply a more complete work in terms of the current signal,
and technically, it is superior to conventional technology.
About the A-D type relays based volume
control:
In NFB-10WM is
applied an exact A-D (analog to digital) type relays based volume
control. It has a built-in CPU to pick up the analog volume pot
position, through a ADC change to digital signal for the CPU count
and control two relays volume boards through changing the DALE
resistors to control the volume.
This A-D type relay-based
volume control has 32 steps, and with the High/Low gain switch is just
like a 64-stepe, wide-range volume pot which can suit most users
requests.
This A-D type relay-based
volume control can avoid channel imbalance and sound better than normal
volume pots.
For long long life, we apply a ALPS
27 volume as the analog position volume pot.
ALPS 27 analog position volume pot
Exact volume control
board
The
NFB-10WM Functions:
Front
plate:
Power switch: Power ON/OFF
the NFB-10WM.
Balance Headphones socket: Output for balance headphones.
Gain switch: Select
gain between low gain (+0DB) and high gain
(+12DB).
Volume knob: Control
the volume level of the headphone and variable DAC output.
1/4' headphone socket : For single-ended headphones.
Preamp button: Select the NFB-10WM output between
dedicated DAC output or headphone
output ,the dedicated DAC output level can be chosen
between variable and fixed .
Selector switch: Select
source between USB, coaxial and optical.
Rear:
USB socket: For USB input.
Opt socket: For optical input.
Coax socket: For coaxial input.
Line out sockets: For dedicated DAC output. (The DAC output level can
be chosen between variable and fixed , see below).
How to set the NFB-10WM DAC output
as variable line level only?
The
NFB-10WM has dedicated DAC output for RCA ,XLR and ACSS. In
default its output level setting is at variable only (if yours amp
or active speakers without volume control, we advice setting to
variable output only). But owners can set
it to can select
between variable and fixed or output variable line level only
.
See the photos, pull off the jumper to
set the DAC output to variable only.
Please note, the ACSS output is only variable at fixed
level mode. ( The NFB-10WM always working with ACSS in every modes, in
variable output mode, the ACSS signal just separated between ACSS
modules and the ACSS output sockets , so can't degrade on sound
quality, just choice what mode you wanting . )
Setting the Fixed and variable
output
If we only use the RCA or 1/4' headphone output, is the NFB-10WM wasted or not
fully utilized?
The NFB-10WM is a real balanced output DAC and headphone amp, it has balanced (ACSS,
XLR and balanced headphone output), single-ended output (RCA and 1/4'
headphone output). There are 4 ACSS modules in the NFB-10WM
for balanced output, and all the ACSS modules have balanced input, so
even through single-ended output,
the WM8741 DA chips will perform fully.
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