Audio-GD R-8HE MK3

This new version of the R-8HE, the MK3 version, has received many technical improvements and has been extensively tested and measured to provide a sound reproduction of great musicality. The power supply is stabilized by a discrete servomotor, offering performances comparable to those of batteries and efficiently powering the digital/analog conversion sections. The analog circuits are always powered by pure Class A power supplies to ensure the best possible sound reproduction.

This Audio-GD R-8HE, with its extremely careful design, takes up the key elements of its predecessor, the R-7HE, whose audio quality it inherits, while seeing its performance revised upwards and its price reduced. In the R-8HE, there are 4 Ladder DAC modules, this time in version 2, as well as the regenerative power supply. These two elements, at the heart of the device, allow it to offer great transparency, high dynamics and incredible sound richness, with a reproduction close to what can be offered by analog.

The R-8HE also includes surface components, making it possible to reduce the price of the device without degrading its audio quality, and therefore making it more accessible to buy a DAC with a regenerative power supply.

In addition, the R-8HE has completely separate power supplies. The digital circuit and the analog left and right channels each have a transformer. The signal circuit and transformers are separated by 5mm thick Aluminium plates, ensuring a high level of insulation. This improves SNR, isolates harmonic interference and reduces noise. The left and right channels are placed completely symmetrically so as to maintain the distance travelled by the cables equal on each side. The R2R DA conversion modules are placed between two Aluminium plates to avoid RF interference.

Version MK3

This new version of the R-8HE, the MK3 version, has received many technical improvements and has been extensively tested and measured to provide a sound reproduction of great musicality. The power supply is stabilized by a discrete servomotor, offering performances comparable to those of batteries and efficiently powering the digital/analog conversion sections. The analog circuits are always powered by pure Class A power supplies to ensure the best possible sound reproduction.

Improvements and new features of the MK3 version:

• New feature New chassis design making the product more modern.
• New feature A new display has been added to the R8 mk3. Input and sample rate are now displayed simultaneously. (Multifunction display with 2 lines).
• New feature Discrete components are used within a balanced power transmission design. This MK2 version embeds 4 groups of discrete and independent hardware DSD decoders and 8 groups of discrete R2R DAC modules forming a 2 channel balanced push-pull decoder.
• New feature An option - which can be activated or not - allows you to enjoy a sound signature close to the analog sound of vinyl.
• New feature Function to display the sampling rate of the input signal.
• Upgrade Both the USB and HDMI inputs have isolators and two sets of independent linear power supplies to prevent interference.
• The USB uses a bidirectional isolator, not only transmitting the I2S signals to the FPGA but also receiving the FPGA's synchronous clock signal for greater accuracy in signal transmission.
• Upgrade The digital circuitry of the entire DAC is composed of an FPGA and 5 CPLDs to separate the different functional circuits and avoid interference. The FPGA operates using the parallel data processing mode for clearer sound.
• Upgrade Two high-end Accusilicon clocks with frequencies of 90 and 98MHz ensure the synchronization of the whole device for a detailed and transparent playback.
• Upgrade DSD signals use the built-in asynchronous clock for better synchronization.
• Upgrade The SPDIF inputs support the playback of DoP streams.
• Upgrade All the parameters of the device can be changed using the buttons on the front of the device.
• Upgrade A port for updating the firmware has been added to the outside of the device.

NOS & OVERSAMPLING MODE
The R8 offers several Oversampling or NOS (Non-Oversampling) modes. If you wish to choose Oversampling, simply select the value “O”. If you want to choose the NOS then you have to choose the value “N”. You can then select one of the following modes to adapt the playback to your listening experience

THE R-2R LADDER STORY
The R-2R DAC has become popular and was originally designed long time ago by MSB, and did not include the wonderful correction design of the modern MSB technology.  In the High-End of the shelf (finished products) market, the R2R design is usually much more complex when outstanding performance is offered. Some manufacturers are using shift registers design to realize ladder compensation. A less complex, unfortunately also a less performing.

A far better design switches resistors in parallel mode; an ultra-fast FPGA chip 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 particularly complex, however when it is done properly it can correct every bit of the ladder. (Photo below shows a FPGA design with R2R ladder). With incredible speed and accuracy the R-28 will correct the unavoidable imperfections of the basic R2R ladder caused by tolerance of resistors; avoid glitches at ultra-high speed to deliver unrivaled musical performance.

TOLERANCE OF RESISTORS IN LADDER
Some manufactures claim to achieve good performance becuase they use lowest tolerance ladder resistors. The following calculation example will cover this. At 16 bit the tolerance of 1/66536, 0.1% (1/1000) it is by far not enough to achieve decent performance. Even using resistors with 0.01% (1/10000) tolerance, lowest tolerance available today,cannot deliver the desired performance This is just 16 bit, imagine a 24 calculation! To process 24 bit resolution it would require resistors with a tolerance of 0.00001%. This is purely theoretical; if this tolerance would exist the discreteness of the switch logic chips will already have too much internal impedance and will shake-up such design.The tolerance of the resistor will never solve Imperfections of a ladder.

The solution lies in the correction 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 with parallel FPGA processing.

ULTRA FAST SIGNAL PROCESSING
FPGA stands for Programmable Array Logic. Nowadays the FPGA is widely adopted in audio devices. 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 capabilities or improve the performance of the device without replacing any hardware. Versatile and future proof design.

High performance SPDIF interface, replacing traditional less good performing SPDIF interface chips like DIR9001, WM8805 or AK411X,etc.

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.

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 the sound according to your taste.

ANALOGUE OUTPUT STAGES
The analog output stages are as important, they have a tremendous influence on the final 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 compon ents are applied in the analogue section.  The high speed unique ACSS ((Audio-gd Current Signal System) output stages are non-feedback and current driven. Unique performance because almost all other designs need to convert the signal multiple times from and to current and/or voltage, resulting in less detailed and less transparent 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 without (negative) feedback to achieve purest and a real live sound reproduction. The 4 OPA op-amp’s are DC servos, this way no coupling-capacitors are needed and DC output is automatically biased. The listener will be presented a strikingly transparent and neutral sound.

ACSS – Current Amplification
Audio-GD has developed an advanced current-driven amplifier technique. Also known as ACSS, Audio-GD Current System Signal. This special technique ensures that the signal travels a much shorter path and that ensures a more transparent, faster and more neutral reproduction. A similar technique is used by, for example, KRELL. The Current Conveyor technology mostly components are the current mirror. The Current Conveyor technology isn’t a new technology, at 1966 , professor K.C. Smith and A.S.Sedra publish the concept “current mode analogue circuits “.

REGENERATIVE POWER SUPPLY
An integrated regenerative power supply is a proprietary electric generator built into the unit to avoid any noise from main power and deliver ultra-low noise and clean AC wave to feed the preamp. It will regenerate the main power and block noise from the power line, this way the preamp is able to reproduce the most neutral and analog sound you can imagine. First a transformer converts main voltage. DC conversion is done by class A PSUs power supplies.

A discrete balanced regenerative wave generator produces the new ultra-low noise wave form at 400Hz. The 400Hz frequency was chosen because they have better efficiency compared to traditional 50Hz and at this frequency, 400Hz, it will boost the sound to reproduce real and pleasant analog sound. The balanced gain amps with powerful output stages are driving the regenerative transformers to produce the extreme clean AC power. The extreme regenerated clean AC power is send to separate class A PSUs power supplies for both left and right channel. The discrete class-A DC power supply with high input impedance will avoid any noise and allow the amplifier stages to have low output impedance at very high speed and linear at frequency spectrum.

TECHNICAL SPECIFICATIONS