Pro-Ject DAC Box RS2 black

With the Pre Box RS2 Digital, Pro-Ject had pulled off a double feat: a compact, EISA award-winning converter and preamplifier whose digital section rivaled that of much larger devices. The DAC Box RS2 builds on this proven foundation, but removes the preamplifier and headphone amplifier to retain only the fixed-output converter. Fewer functions, then, but a tighter focus: pure conversion.

Dual mono and ESS Sabre conversion

The DAC Box RS2 uses two ESS9038Q2M chips in a dual-mono configuration, with separate signal paths for the left and right channels. This design choice, uncommon at this price point, improves channel separation and reduces crosstalk between channels. Format support is extensive: PCM up to 32-bit / 768 kHz and native DSD up to DSD512 via USB, covering virtually all high-resolution files available on the market or via streaming.

The circuit operates in fully balanced mode, from conversion to output. Analog outputs are available in XLR (balanced) and RCA, both at fixed level, which means a preamplifier or integrated amplifier is required downstream. Total harmonic distortion (THD+N) is specified at less than 0.0008% in transistor mode and less than 0.001% in tube mode, measured at 2 V RMS / 1 kHz.

Transistors or tubes: two sonic characters

The output stage can be switched between transistor mode (based on discrete components) and tube mode using four 6922EH tubes. Transistor mode offers an output impedance of 180 Ω and the best distortion measurements; tube mode rises to 220 Ω with a slight increase in THD+N. The difference between the two is not just a simple tonal shift: tube mode changes the harmonic behavior of the signal and the way transients are reproduced. The benefit of this dual option is being able to tailor the sound rendering according to the type of music or the rest of the system, without changing devices.

The 6922EH tubes are common references and easy to find as replacements. Pro-Ject did not opt for rare or proprietary tubes.

Eight digital filters and MQA decoding

The DAC Box RS2 offers eight selectable digital filters, including an optimal transient filter developed by the creators of the MQA format. The choice of filter influences impulse response and behavior in the high frequencies: some prioritize time-domain accuracy, others a more gradual roll-off. Changing the filter takes a few seconds via the menu.

MQA decoding is fully supported (hardware unfolding), which means the device can decode MQA streams without relying on third-party software for the first unfolding stage. The proprietary upsampling function allows PCM and MQA content to be oversampled with appropriate filtering. The device carries Roon Tested certification.

Six digital inputs, extensive connectivity

The rear panel brings together six digital inputs. The asynchronous USB 2.0 input is the most versatile: it accepts PCM up to 32-bit / 768 kHz and native DSD up to DSD512 (in DoP or native mode). Two optical S/PDIF inputs, one coaxial, and one balanced AES/EBU complete the offering, all limited to 24-bit / 192 kHz.

The sixth input is an HDMI port carrying an I²S signal, intended for connection with Pro-Ject’s CD Box RS2 T transport. Via this link, the DAC Box RS2 provides its master clock (16.9344 MHz) to the transport, synchronizing both devices to a single time reference. This I²S bus over HDMI is proprietary: it works only between components in Pro-Ject’s RS2 series and is not compatible with I²S connectors from other brands.

Signal processing and jitter management

The USB signal is processed by a multi-core XMOS microcontroller. Re-clocking is handled by an Altera MAX II CPLD (a complex programmable logic device), which regenerates the clock signal before conversion. This XMOS / CPLD combination is designed to reduce jitter, whether with standard PCM streams or MQA content.

A compact format and a readable display

The aluminum chassis measures 206 × 72 × 222 mm and weighs 1.52 kg without its external power supply (20 V / 3 A). This reduced format, typical of Pro-Ject’s Box Design range, allows the DAC Box RS2 to be stacked with other elements in the series (CD Box RS2 T, Stream Box S2 Ultra) without cluttering a hi-fi cabinet. The device is available in black or silver.

The front display shows playback information in real time: active source, sampling rate, bit depth, selected filter. Menu navigation is quick. An aluminum remote control is included, so there is no need to get up to change source or filter. The external power supply uses a universal format (110-240 V / 50-60 Hz), and standby power consumption remains below 0.5 W.

Technical Specifications

Digital / Analog Conversion

• Dual mono DAC: 2 x ESS Sabre ESS9038Q2M
• Fully balanced architecture
• PCM support up to 32-bit / 768 kHz
• DSD compatibility up to DSD512
• Full MQA decoding (hardware unfolding)
• 8 selectable digital filters
• PCM and MQA upsampling with proprietary filtering

Output Stages

• Output selection:
  • Transistors (solid state)
  • 6922EH tubes
• Built-in tubes: 4 x 6922EH
• Discrete balanced output buffer
• Output impedance:
  • 180 Ω (transistor)
  • 220 Ω (tube)

Digital Inputs

• 1 x asynchronous USB Audio 2.0
  • PCM 32-bit / 768 kHz
  • DoP and Native DSD up to DSD512
• 1 x HDMI I²S
  • Compatible with CD Box RS2 T
• 2 x optical S / PDIF
  • Up to 24-bit / 192 kHz
• 1 x coaxial S / PDIF
  • Up to 24-bit / 192 kHz
• 1 x balanced AES / EBU
  • Up to 24-bit / 192 kHz

Analog Outputs

• 1 x stereo RCA
• 1 x balanced XLR

Signal Processing

• Multicore XMOS controller with advanced RISC architecture
• Advanced re-clocking via CPLD MAX II Altera
• Master clock:
  • 16.9344 MHz for CD Box RS2 T

Audio Performance

• THD+N (20 Hz – 20 kHz):
  • < 0.0008% (transistor)
  • < 0.001% (tube)
• Measured level: 2 V RMS / 1 kHz
• Ultra-linear, low-noise design

Display and Ergonomics

• Large high-quality display
• Fast and responsive interface
• Premium aluminum remote control included

Power Supply

• External power supply: 20 V / 3 A DC
• Mains compatibility: 110 – 240 V / 50 – 60 Hz
• Power consumption:
  • Max. 1.2 A DC
  • < 0.5 W in standby

Dimensions and Weight

• Dimensions (W x H x D): 206 × 72 × 222 mm
• Weight: 1.52 kg (excluding power supply)