Audio-GD R-8 MK3: Balanced R2R DAC with FPGA

Audio-GD R-8 MK3 is a high-quality balanced R2R DAC with an exceptional design that delivers musical and accurate sound reproduction.

To completely eliminate the effect of jitter on the incoming signal, the R-8 MK3 uses an asynchronous clock system. The asynchronous clock system first reads and stores the source signal data in RAM, ignoring the clock signal, and uses high-performance Accusilicon oscillators on the RAM output. Since the data and clock are controlled by the FPGA, the impact of jitter is negligible. The key to this transmission method is to ensure data integrity for clear, natural sound reproduction.

This version of the R-8 MK3 has gone through an extensive period of testing, measuring, listening and tuning at all levels of the circuit. It uses a regulated power supply with discrete servos for battery-like operation. The converter stage uses this regulated power supply, while the analog circuits use a clean Class A power supply. The improvements and new features of the R-8 are as follows:

• Discrete components integrated into a balanced design: Four sets of discrete, independent hardware DSD decoders and eight sets of discrete R2R conversion modules to create a balanced two-channel push-pull decoder. The noise level is comparable to that of a battery, without the disadvantages of a battery power supply.
• You can turn on a mode that allows you to enjoy the characteristic sound of a vinyl record player.
• The USB and HDMI inputs have independent isolators and linear power supplies to limit interference: USB uses a bidirectional isolator that sends the I2S signal to and receives the clock signal from the FPGA. The USB interface no longer uses its own clock, but uses a synchronous signal for more accurate transmission and improved sound quality.
• The R-8 MKII now displays the sample rate of the original signal.
• The digital-to-analog conversion circuit uses an FPGA and five CPLDs to sharply limit interference. FPGA works in parallel. I2S transmission is carried out sequentially. This design allows for faster signal processing and is less sensitive to timing accuracy. The I2S inputs are organized into two sets of 32-bit parallel data, SPDIF into two sets of 24-bit parallel data. DSD signals are organized into two parallel 64-bit sets. This design provides a more neutral and accurate sound with better dynamics.
• Two Accusilicon clock generators with frequencies of 90 and 98 MHz ensure perfect synchronization of the entire device. New clock control design provides better stability for better transparency.
• DSD signals use an asynchronous clock for greater accuracy.
• SPDIF supports DoP playback.
• All digital modes are accessible and changeable using the buttons on the front panel.

The R2R design has many advantages, the most obvious of which are:

• R2R does not convert the clock signal into an output signal.
• This design is not sensitive to jitter.
• The output signal is more accurate.

The FPGA and five CPLDs are largely responsible for the high audio quality provided by the R8-8 MK2. In particular, they are responsible for the following:

• The FPGA integrates a high-performance SPDIF demodulator.
• They combine a timing system and FIFO technology to output data for precise timing and hence effective jitter suppression.
• The R-8 MKIII has built-in 2X, 4X and 8X digital filters, as well as various NOS modes.
• One of the modes allows you to simulate the sound of a vinyl player.

The analog output stage is connected directly behind the DA-7 modules, without the use of SMD components. A high-speed ACSS amplifier is used to amplify and process the signal. It uses a negative feedback design. The output buffer uses a single-ended FET design, with each group connected in parallel for lower output impedance. The DAC includes 4 AOPs to provide the DC servo function and therefore does not require a coupling capacitor to avoid additional noise or audio coloration.

Characteristics of Audio-GD R-8 MK3:

• Product Type: DAC
• Inputs: 1x HDMI (I2S)/ 1x USB (I2S)/ 1x XLR/ 1x BNC/ 1x coaxial/ 1x optical
• Outputs: 1x XLR/ 1x RCA/ 1x ACSS
• SNR: > 120 dB
• Output impedance: <5 ohms (XLR, RCA)
• Output level: RCA: 2.5 V/ XLR: 5 V/ ACSS: 2+2 mA
• Frequency response: 20 Hz – 20 kHz
• THD: <0.1%
• Input Sensitivity: Coaxial: 0.5Vp-p (75 Ohm) / Optical: 19dBm / USB / HDMI: 3.3V
• Compatible OS: Windows, OSX, Linux, ISO
• Supported sampling rates: USB, HDMI: PCM up to 32bit 384kHz, DSD up to DSD512/ Coaxial: PCM up to 24bit 192kHz/ Optical: PCM up to 24bit 96kHz
• Supply voltage: 220-240V AC 50/60Hz
• Consumption: 40W
• Weight: 12 kg
• Dimensions: 430 x 445 x 80 mm