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Audio-gd products are design and tested based on the AP SYS-2722
specifications (The top-drawer professional equipment in world)
Pros and cons of R-2R
1.R-2R will not convert the
clock signal into the output signal.
2. R-2R is not sensitive to
jitter while Delta-Sigma DA is much more sensitive to jitter.
3. The output signal is much
more precise compared to Delta-Sigma DA .
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
The R-2R DAC
is very popular nowadays and available from DIY kits and completely
up to of the shelf 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 of the shelf (finished products)
market, the R2R design is much more complex only to reach best
performance. A basic R2R ladder is simply not sufficient enough to
achieve good performance and sound quality! Some manufacturers are
using shift registers design. A less complex and less performing
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 tolerance of resistors,
glitches to achieve best performance.
Accuracy of the ladder resistors
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 request 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 can 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 resistor.
is to correct the ladder and not only depend on the tolerance of
resistors. Itกฆs a combination of both: Ultra-low tolerance resistors
controlled by a correction technology using very high speed FPGA are
applicable in in our design.
Importunacy of the FPGA :
FPGA stands for Programmable Array Logic.
FPGA is applied in a lot high end grade DACs; like the popular
ROCKNA WAVEDREAM DAC.
hardware design is fully controlled by complex software. A huge
advantage is the fact the software in the FPGA can easily be
upgraded offering new features or improve the performance. Such
design is much flexible and future proof!
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
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!
Built in an excellent real balance discrete
signal last stage is the analog output stages, they can much 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.
The high speed special ACSS output stages are non-feedback and
current driven design.
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 good
The output stages had built in 4
pair 15W transistors for offer strong drive ability .The
diamond different design can avoid switch distortion , it working as
the class A but don't want large idle current . The balance drive
mode can kill the noise and distortion in the end of the headphone,
much improve the sound stage, background and the transparency ,ect.
0.05% tolerance volume
4 channels volume boards built in the unit for the balance volume
control. They are control by digital signal but applied relaies
control the resistors in analog area . The 0.1% Vishay or KOA
resistors working in parallel mode to got the 0.05% tolerance .
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.
There are in
total 11 group ultra-high speed and ultra-low noise PSUs built in
and applied double stage PSUs technology for remove the power
interrupt ,get much clean power supply for the digital parts .
are two group pure class A PSUs built in for the analog amps .