NFB-11 applies the newest ESS high-end Sabre32 DA chip ES9028 which
can support up to 32Bit/384KHz input .
be achieve the best performance of ES9028 , must work in current
output mode. in voltage output model, there is -12DB THD+N loss .
The standard current model design usually need 3 amps (OPA)
, the first amp implements I/V conversion, the ES9028 output
current signal to voltage signal .
The second amp is responsible for conversion balanced signal
,to single-ended signal and implement the low pass analog filter ,
then go through the volume control fed to the third amp, (the
headphone amp ).
Every amp usually have two gain stages built in to the ES9028
chip . Signal must go through total of 6 gain stages and finally
arrive at the output stage.
The NFB-11 applies Non-feedback ACSS design. The ES9028 feed
to the ACSS circuit without any OPAs .
The ACSS circuit naturally working in current mode . The ACSS
amp only have one current gain stage , the ES9028 output signal only
goes through one stage .
The shortest signal path can reproduce the best detail and
dynamics almost without any sound coloration .It showes the real
performance of the ES9028 dac.
So our ACSS design is the best combo with ES9028 to achieve
the best performance .
Upper is the diagram of a standard ES9028 headphone amp
design. The bottom is the NFB-11 design .
ACSS also 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 to the human's ears.
Here lyes a conflict of the classic circuits.
But the ACSS opens a new field, it can offers the least
coloration 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 and harsh )
The output buffers are Non-feedback. For low impedance we
applied a diamond output stage which is less colored than most
conventional circuits. It is built with 4 pcs 20W (in total 80W)
high speed Toshiba transistors, To early drive mostly the
The DAC is without de-coupling caps to avoid coloration.
There are two OPAs built in as the DC servo to control offset .
The 32bit / 384K USB interface outputs a I2S signal to the
Fully Discrete ACSS headphone amp.
applies the excellent D/A chip ES9028 and excellent analog output
stages, but these are not the only elements to the best sound. The
power supply is a key element . Even when applying the best D/A chip
and the best amp, if matched to a average power supply, the total
sound characteristics may still be average at best ,maybe musical
but can't be neutral and detailed. That is why it is easy to find
hi-end gear without the best chips , but with plenty of dedicated DC
The NFB-11 uses 6 groups of high-quality PSUs with
dedicated DC supply . Digital and analog voltages each have
separately isolated internal power regulatiors.
The digital power had 4 groups high speed PSU groups(
double stages PSUs) this allowes to avoid the interruption from the
power supply that can cause the jitter . It offers blacker
background and much cleaner sound. In addition this double stages
PSUs are only applied in our USD1500+ products.
This massive power supplie design is usually only applied
in the USD1000+ products .
The analog power supply is more important for sound
reproduction . In NFB-11 the +15V and -15V for the analog output
stages are high speed Discrete PSUs. They offer pure and quick
power supply to drive any headphone with high accuracy .The high
voltage power supply can drive most headphone from 15 to 600 ohms as
Strong power supply.
About volume in ACSS circuits:
control is very important.
In ACSS, it is placed at the ACSS module output, where the
output is the current signal stage not the voltage stage . 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
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-11 is simply a more
complete work in terms of the current signal, and technically, it is
superior to conventional technology.
ALPS 27 volume pot