USB isolator upgrade for Amanero combo 384 as default configure since 11st. Dec.
USB isolator can avoid the computer electric interrupt feed in the DAC cause the sound quality worse . In AB compare , it can improve on sound transparency slightly .
After USB isolator upgrade, the USB spend the USB power supply, and can not support phones because the power limit of the phones .
Audio-gd products are design and tested based on the AP SYS-2722 specifications (The top-drawer professional equipment in world)
Pure analogous Regenerative power supply :
The regenerative power supply like a proprietary electric generator built in the unit.
It can block most disturb from the power line , supply the ultra clean power supply for the audio amps , reproduce the most neutral and analog sound like audio signal for the system and the users.
In the regenerative power supply design, the AC power through the regenerative input transformer , conversion to DC power ,through the class A PSUs power supply for the regenerative wave generator and driver stages .
A balance regenerative regular wave generator produce the ultra low distortion 50Hz wave ,through the balance gain amps and the strong output stages , drive the regenerative transformers produce the clean AC power supply feed to the separate class A PSUs power supply for the L and R channel preamps .
The class A parallel connection PSU has very high input impedance to avoid disturb through the PSU from affecting the signal parts and low output impedance with very fast speed and high linear, it is a very clean power supply.
Audio-gd on the regenerative power supply design points :
1, Through analyzed the AP SYS-2722 ,do a lot practises ,test and listen , full analog design of the regular wave generator have much lower distortion than the digital generator.
2, Digital drive stages have higher efficiency , but full analog drive stages have much better analog sound like .
3, 400Hz regenerative wave have higher efficiency , 50Hz regenerative wave had much far away the human ears sensitivity area than the 400Hz, boost the sound have much better analog sound like.
Pros and cons of R-2R DAC :
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 market:
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 (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 R2R 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!
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 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, 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 staging.
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 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:
Uses four R-core transformers (In total 295W ) and more than 95,000uf audio grade NOVER capacitors are used to ensure ample and smooth power delivery.
15 groups discrete class A PSUs power supply for the regenerative drivers and the digital / analog audio signal parts.
This results in ultra-high speed and ultra-low noise performance. Clean and independent power for all different parts to achieve highest quality.
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.