R-7 (2020 version)

Fully Discrete R-2R Resistor Ladders DAC

Fully Discrete DSD Native decoder

Fully Discrete Real Balance  Current Transmition Design

Support external 10MHz clock input (50 ohm)

The FPGA process data in parallel mode

All Digital Settings accesible By Buttons On Front  (No need  to open the chasis).

Firmware update port assembled on rear, update  firmware no need  to open the chasis.

Accusilicon clocks:
       
Crystek clocks:


Click to download the driver of  Amanero combo 384

What's new in R-7 (2020 version):
 1,     Support 10 MHz clock input.
  2,    The FPGA process data upgrade to parallel mode.
         The IIS data is series transmit mode, every data must need one clock cycle to process or transmit, one frame data ( Include L and R data) must need 64 clock cycle to process or transmit, so the data has effect by the 64 clock cycles.
         But the parallel data process and transmit mode only need one clock cycle can finish the one frame data process and transmit, that can avoid the effect of clock stability .
          The IIS input (Include USB and HDMI-IIS) has recombine become dual 32bit parallel data once input , and the SPDIF input after decoder, has recombine become dual 24bit parallel data, and the DSD input has recombine become dual 64bit parallel data once input.
          The parallel process and transmit mode can improve the sound quality on the transparency and detail but still analog.
3,       Full new configuration clock manage design built in, improved on the clock timing.
4,      DSD asynchronous clock technology has apply that improves the sound quality obviously.
5,      DOP support from coaxial input .

R-7 reviews : https://www.head-fi.org/threads/new-audio-gd-r2r-7-flagship-resistor-ladder-dac.853902/page-180
6 Moon Reviews :    http://www.6moons.com/audioreviews2/audio-gd/1.html


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 while Delta-Sigma D/A is 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 and all the way  up to 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 reaches  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 lower  performance  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 (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 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.
            The solution 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 R-7:
                 FPGA stands for Programmable Array Logic. 
            Nowadays the FPGA is applied in a lot high end grade DACs; like the popular ROCKNA WAVEDREAM DAC. 
            The internal 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!
            R-7 has  no built in  mute switch to  keep the signal without degradation.



　

FPGA tasks 
                The FPGA  is responsible for:
           1. High performance SPDIF interface, replacing traditional  SPDIF interface chips like DIR9001, WM8805 or AK411X wich are lower in performance in comparison to FPGA.

           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 stages,  which can greatly 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 transistors are applied. The high speed special ACSS output stages are non-feedback and current driven design. 
           Almost all other designs need to convert the signal multiple times from and to current or voltage, resulting in less detail and less defined  sound stage . 
          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 4 OPA opampˇs 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 D/A modules to allow  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 23 separate power rails. 20 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.
           

Finishing touch:
               The R-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.