Pro-Ject Pre Box S2 Digital
Compact DAC preamplifier from Pro-Ject fitted with two ESS9038Q2M converters, equipped with USB, coaxial and optical inputs as well as a dedicated headphone output.
Description
The Pre Box S2 Digital is a compact digital-to-analogue converter from Pro-Ject, designed to serve as a digital preamplifier and headphone listening station. It receives a digital signal via USB, coaxial or optical, converts it and then outputs it as a variable analogue signal or directly to headphones, without requiring a separate power amplifier for the latter function.
Its conversion relies on two 32-bit ESS9038Q2M differential DACs, paired with an analogue output stage based on the SABRE9603Q operating in class A. The USB input accepts DSD up to DSD512 (DSD1024) and PCM up to 32-bit/768 kHz, while the optical and coaxial inputs are limited to 24-bit/192 kHz PCM. Seven digital filter settings can be selected directly from the front panel, allowing the transient response to be adjusted according to listening preferences.
The headphone output, in 6.3 mm jack format, delivers 6.6 mW into 600 ohms and 100 mW into 32 ohms, with a recommended minimum impedance of 8 ohms. Total harmonic distortion is stated at 0.0003% at 0 dB (2 V RMS, 1 kHz), and the dynamic range reaches 124 dBA, figures that reflect very low background noise during listening. The variable line output on RCA delivers a voltage of 2.05 Vrms, and the frequency response extends from 20 Hz to 20 kHz.
This DAC is aimed at digital audio enthusiasts looking to improve listening from a computer or digital source, as well as users of low-impedance headphones seeking a high-performance dedicated output rather than a simple amplifier headphone jack. Its compact format also suits it to a desk as well as a small desktop or bedside setup.
Technical specifications
| Digital inputs | 1 USB port (B), 1 coaxial port (RCA), 1 optical port (TOSLink) |
| DAC | 2x ESS9038Q2M 32-bit |
| USB | up to DSD512 (DSD1024), PCM up to 32-bit/768 kHz |
| Optical | PCM up to 24-bit/192 kHz |
| Coaxial | PCM up to 24-bit/192 kHz |
| Filter settings | 7 options selectable from the front panel |
| Frequency response | 20 Hz - 20 kHz |
| Analogue outputs | 6.3 mm headphone output (front), 1 variable output (RCA) |
| Output voltage | 2.05 Vrms |
| Recommended minimum headphone impedance | 8 ohms |
| Headphone output power | 6.6 mW / 600 ohms; 100 mW / 32 ohms |
| THD | 0.0003% at 0 dB, 2 V RMS, 1 kHz |
| Dynamic range | 124 dBA |
| External power supply | 5V/1A DC (included) |
| Dimensions (H x W x D) | 103 x 37 x 122 mm (knob and connectors included) |
| Weight | 366 g (without power supply) |
What to check before buying used
On this type of converter-preamplifier, the 6.3 mm headphone jack on the front panel is the most heavily used connection: check that it shows no play or crackling when the plug is inserted. Also check that the seven selectable digital filters work correctly, as well as the volume knob, whose track can wear over time. Finally, test the three USB, coaxial and optical inputs separately, as a fault on a single digital input is not uncommon on a unit that has seen heavy use.
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