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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. It¡¦s 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 in the R2R 7:
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!
FPGA tasks in the R2R 7
The FPGA in the R2R 7 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!
Fully discrete output stages
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.
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.
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 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
The 4 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
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 3 high quality low noise,
low flux leakage, R-cores transformers.
In total 130W
power to supply all digital parts and the left and right analog
boards. The DC power is distributed over 19 separate power rails.
All are pure class A low noise regulated power; fed by 3 groups
linear power supplies.
in ultra-high speed and ultra-low noise performance. Clean and
independent power for all different parts to achieve highest
The R2R-7 has completely separated power supplies .Digital, left and
right analog channel have their own dedicated transformer. All
boards and transformer compartment are separated by 5mm thick
aluminum plates for high isolation degree.
It improves the signal-to-noise ratio, isolate the harmonic
interference and reduce noise, which will make the sonic background
cleaner and blacker.
The Left and Right analog parts are placed symmetric beside the
digital board to keep the wires and distance identical to ensure
equal output performance on both channels .
The R2R DA modules are assembled between two aluminum boards to
avoid any RF interferences.