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Amanero
combo 384
Audio-gd products are design and tested based on the AP SYS-2722
specifications (The top-drawer professional equipment in world)
        
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the R2R 2DAC :
The discrete R-2R design had the better detail and transparency than
the classis R-2R chips. We are consider in this middle/ low range
price, users may like the sound more smooth and analog , so we
increase the even harmonic and odd harmonic, spend a lot time to
adjust and test the harmonic and frequency band , listen the
sound quality and flavor for finally confirm the parameter..
A lot people may know the
even harmonic , just like the tube design, proper even harmonic
especial 2x harmonic made the sound tube like and smooth .
But a lot people even
some designers don't know the proper odd harmonic especial 3x
harmonic can make the sound lively.
If you like to looking
for the good specs, R2R 2 may not as good as the same price range
ESS9028 Sigma Delta design, but its sound is analog and smooth.
Pros and cons of R-2R DAC :
Advantages:
1.R-2R will not convert the clock signal into the output
signal.
2. R-2R is not sensitive to jitter in contrast to
Delta-Sigma D/A with much more sensitive to jitter.
3. The output signal is much more precise compared to
Delta-Sigma D/A
Weaknesses:
1.THD today is extremely good with Sigma Delta chips; R2R
ladders are good too but not as good.
2. Glitches and accuracy of the ladder resistors are very
difficult to avoid and require complex technology to resolve it.
R-2R basic design in the market:
The
R-2R DAC is very popular nowadays and available from DIY kits up to
completely high-end products.
In the low range DIY market, the R-2R design is often
based on old technology designed a long time ago by MSB and only
includes basic R2R ladder design and do not include the wonderful
correction design of the original MSB technology. This design uses
data shift registers logic chips in series mode to convert the data
to an analog signal. The structural R2R technology issues cannot be
avoided, and performance is solely depending on the accuracy of the
ladder resistors.
In
the High-End market the R2R design is much more complex and achieves
better performance. A basic R2R ladder is simply not sufficient
enough to achieve good performance and high sound quality! Some
manufacturers are using shift registers design. A less complex and
less efficient design based on traditional logic chips working in
serial mode to correct the ladder.
A far better design switches resistors in parallel mode. An
ultra-fast FPGA controls and corrects the R2R ladder. The parallel
design mode controls every bit respectively and therefore achieve
unprecedented performance. (In parallel mode only 1 clock cycle is
needed to output all data; serial design mode needs at minimum 8 up
to 24 clock cycles) The parallel design is much more complicated.
Once designed properly it can correct every bit of the ladder.
Photo below shows a design with such FPGA, can correct the
unavoidable imperfections of the R2R ladder caused by intolerance of
resistors glitches and achieve best performance.
Accuracy of the ladder resistors (tolerance):
Many
people believe the tolerance of the resistors in the ladder is most
important to reach best performance. Nowadays 24 bit resolution is
standard. What tolerance is needed to achieve 24 bit resolution?
When we look at 16 bit the tolerance of 1/66536, 0.1%
(1/1000) is far not enough, even a tolerance of 0.01% (1/10000), the
best tolerance available in the world today, still cannot handle 16
bit correctly; we are not even calculating 24 bit here!
The tolerance of the resistor will never solve
Imperfections of a ladder. This would require resistors with a
tolerance of 0.00001% and ability to handle 24 bit resolution. This
is only in theory because the discreteness of the switch logic chips
have already too much internal impedance and will destroy the
impossible tolerance of a the resistor.
The solution is to correct the ladder and not to depend
on the tolerance of resistors. It¡¦s a combination of both: Ultra-low
tolerance resistors controlled by a correction technology and very
high speed FPGA which is applied in in our design.
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Importunacy of the FPGA :
FPGA stands for Programmable
Array Logic.
Nowadays the FPGA is applied in a lot of high end DACs;
like the popular ROCKNA WAVEDREAM DAC.
The internal hardware design is fully controlled by
complex software. A huge advantage is the fact that the software in
the FPGA can easily be upgraded offering new features or improve the
performance. Such design is much more flexible and future proof!
FPGA tasks
The FPGA is responsible for:
1. High performance SPDIF interface, replacing
traditional less good performing SPDIF interface chips like DIR9001,
WM8805 or AK411X,etc.
2. Full re-clocking process with FIFO design applicable
on all inputs. This way the output data keeps fully synchronized
with the clock signal to reject any jitter.
3. Built in 2X, 4X and 8X oversampling and digital
filters and on top of this 4 different true NOS (only analog 6dB
filtering) modes. To completely configure it to your liking!
Fully discrete output stages
The
signal last stage is the analog output stage, that can effect the
whole DAC sound quality.
After d/a conversion by the R2R D/A modules the analogue
signal is transported by fully discrete matched-transistor output
stages.
DC-coupled design with first class through-hole
components. No SMD components are applied. The high speed special
ACSS output stages are non-feedback and current driven design.
They are Special because almost all other designs need to
convert the signal multiple times from and to current or voltage,
resulting in less detail and less precise soundstage.
The output buffers are single ended FET. Two stages in
parallel to reach very low output impedance. All output stages are
in pure class A design without any (negative) feedback to achieve
purest and a real live sound reproduction.
The 2 OPA opamp¡¦s are functioning as DC servo, this way no
coupling-capacitors are needed and DC output is automatically
biased! Resulting in a perfectly neutral sound.
There are no relays or other switches in the signal path
after DA modules to perform the best and purest sound quality.
Heavy power supplies design:
The DAC has
the high quality low noise, low flux leakage, R-cores transformers
to supply all digital parts and the left and right analog boards.
The DC power is distributed over 8 separate power rails. 5 groups
are pure class A low noise regulated power; fed by 3 groups linear
power supplies.
This results in ultra-high speed and ultra-low noise
performance. Clean and independent power for all different parts to
achieve highest quality.
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