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R-7 

Fully Discrete R-2R Resistor Ladders DAC

Fully Discrete DSD Native decoder

Fully Discrete Real Balance  Current Transmition Design

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

4  different types of  algorithms in a  NOS mode, and 3 different types of oversampling.

have 7 distinctive flavours,  Can be selected  by the buttons on front plate.

Firmware update port assembled on rear, you can update  firmware without opening the unit.

Standard version:   USD2580  (With TCXOs, USB Isolator and PSU upgraded) 

        
Crystek clocks:

DA7 V2 released

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.

 

Specifications:

　 

S/N Ratio	>120DB
Output impedance	<5 ohm (XLR ,RCA)
Output Level	2.5V (RCA) 5V (XLR) 2+2MA (ACSS)
Frequency Response	20Hz - 20KHz
THD
Input Sensitivity	0.5 Vp-p ( 75 Ohms, Coaxial ) 19 dBm (Optical) USB1.0 - USB3.0  RJ45 /HDMI : 3.3V
Support Operate Systems (USB)	Windows, OSX, Linux, ISO
Support Sampling	USB & IIS : 44.1kHz - 384kHz /32Bit DSD64-512  Coaxial mode: 44.1kHz - 192kHz Optical mode: 44.1kHz - 96kHz
Power Requirement	100-120V  AC 50/60 Hz 220-240V  AC 50/60 Hz
Power Consumption	48W
Package Weight	Approximately 16KG
Dimensions	W430 X L430 X H93 (MM, Fully aluminium )