Pro-Ject Pre Box S2 Digital DAC/Preamplifier

Small Is Beautiful

Equipment report
Solid-state preamplifiers,
Digital-to-analog converters
Pro-Ject Pre Box S2
Pro-Ject Pre Box S2 Digital DAC/Preamplifier

Pro-Ject, which hails from Austria, has been in existence since 1990. And while it isn’t the first audio firm to specialize in small modular components, it has been especially focused on miniaturized high-performance audio. Currently Pro-Ject has five different “lines” of components—the RS Line, DS2 Line, S2 Line, Classic Line, and Elemental line.

All of these Pro-Ject boxes were designed to be used in conjunction with one another to form complete miniature systems. The Pre Box S2 Digital is from the S2 Line, which also includes a streamer (the Stream Box S2 Ultra), a disc player (the CD Box S2), and a stand-alone DAC (the DAC Box S2 ), as well as three just-announced external power supplies for S2 devices. Pro-Ject also has a Phono Box S2, Bluetooth Box S2, AD Box S2 Phono (to digitize phono sources), Tuner Box S2, Remote Box S2 (with iOS and Android Apps), and to control them all the DS/RS remote.

How small is the Pro-Ject Pre Box S2? Official measurements are 4" by 1.4" by 4", which by any standard of measurement is small. The Pre Box S2 is also relatively light at only 500 grams, which is slightly more than one pound. During my time with the Pre Box S2 I held it in place on my desktop with a VPI brick (the brick is a 4" by 4" by 2" wooden box filled with metal plates that weigh several pounds); otherwise it was far too easy to reach for the volume control and accidentally push the unit far away from its original location. If you lack a brick, the Pre Box S2 also comes with a remote control, so you don’t have to touch it. The price for this miniature marvel? $399.

Technical Tour
As its name implies, the Pre Box S2 is a digital preamplifier, but it also includes a headphone amplifier with a full-sized ¼" headphone output based around an ESS9602 chip. The Pre Box S2 includes three digital inputs; coaxial SPDIF, TosLink optical, and USB B. The Pre Box S2 DAC section utilizes the ES9038Q2M DAC chip, which is based on the ES9038PRO chip but designed with the lower power capabilities of a mobile device in mind. This allows the Pre Box S2 to be powered either by a USB connection or by a beefier 5-volt external power supply. Support for DSD up to DSD512 (DSD over PCM) and PCM up to 768/32, as well as MQA decoding, is built into the Pre BOX S2. Besides MQA decoding, the Pre Box S2 also includes seven user-selectable PCM filter settings that can be accessed via a single button on the front panel or remote. With its own proprietary clock circuitry, organic polymer capacitors, and thin-film mini-MELF resistors, the Pre Box S2 may be budget-priced but is not limited in features or performance.

One area where Pro-Ject devoted additional technical focus was the USB input. According to the company, “one of the major problems for USB DACs is the transmission of unwanted noise coming through the USB output. A lot of research of Pre Box S2 Digital went into how to make this noisy connection quieter. After a good deal of head-scratching trial and error, we found the solution in active and passive filtering of the output.” Pro-Ject claims its two-step process reduces noise by up to 75dB at 1kHz.

If you open up the Pre Box S2, you will discover four-layer, gold-plated PC boards fully enclosed inside its thick aluminum case. While I would not recommend dropping a Pre Box S2 out a second floor window to check its ability to withstand shock, I suspect it might very well survive the fall and retain full functionality. It is an extremely sturdily built micro-component.