The Pre Box RS2 Digital combines preamplifier, D/A converter and headphone amplifier: two ESS9038Q2M DACs in dual mono, digital and analogue inputs, Bluetooth and an output stage that switches between valves and solid state.
Pre Box RS2 Digital: what is inside
Conversion is handled by two ESS Sabre chips, one per channel, with separate signal paths for left and right. Over USB the unit accepts PCM as high as 32 bit / 768 kHz and DSD up to DSD512. The USB feed is managed by a multi-core XMOS microcontroller, while re-clocking is done by an Altera MAX II programmable logic device. MQA is decoded entirely in hardware, and the eight selectable digital filters include the one developed by the people behind MQA.
The wired digital inputs are USB, two optical, one coaxial, one balanced AES/EBU and one I²S reserved for the CD Box RS2 T transport, to which the preamplifier also supplies the 16.9344 MHz master clock; Bluetooth 4.0 with SBC, AAC and aptX is added on top. Analogue sources get one XLR and one RCA line input, and the feed to the power amplifier is offered both balanced and single-ended.
The output buffer is discrete and balanced and can run either in solid state or through the four 6922EH valves, according to the listener's taste. The headphone amplifier is DC coupled from input to output, with no capacitors in the signal path and a servo that keeps direct voltage off the 6.35 mm jack. The front display, an aluminium handset and the external 20 V power supply complete the package.
Specifications
- Converters: 2 ESS9038Q2M in dual mono, 32 bit / 768 kHz and DSD512 maximum
- USB input: 1 USB 2.0 Audio, PCM 32/768, native DSD and DoP to DSD512
- I²S input: 1, for the CD Box RS2 T, with 16.9344 MHz master clock
- S/PDIF inputs: 2 optical and 1 coaxial, up to 24 bit / 192 kHz
- AES/EBU input: 1 balanced, up to 24 bit / 192 kHz
- Bluetooth: version 4.0 built in, SBC, AAC and aptX codecs
- MQA: complete decoding in hardware
- Analogue line inputs: 1 XLR and 1 RCA, 15 kΩ impedance
- Analogue outputs: XLR and RCA pre-out, headphones on 6.35 mm jack
- Output impedance: 180 Ω in solid state, 220 Ω with valves
- Headphone power: 90 mW into 300 Ω, 245 mW into 32 Ω, 150 mW into 8 Ω
- THD+N (20 Hz - 20 kHz): below 0.006% solid state, 0.017% valves, at 2 V RMS and 1 kHz
- Output stage: discrete and balanced, valve or solid state
- Valves: 4 x 6922EH
- Power: external 20 V / 3 A DC unit, 110-240 V mains
- Current draw: 1.2 A at most, under 0.5 W on standby
- Size: 206 mm wide, 72 mm high, 222 mm deep, sockets included
- Weight: 1.71 kg, power supply excluded
- Finishes: black, silver
