Усилители для наушников — Pro-Ject Head Box S2 Digital

The Head Box S2 Digital made by the Austrian company Pro-Ject Audio Systems pairs a D/A converter and a headphone amplifier inside a single compact desktop case. It belongs to the S2 generation of the Box Design range, where the Head Box S2 without a converter handles analogue signals only, and it has been made in silver and black.

Key specs that matter

Pro-Ject builds the conversion stage around a 32 bit ESS Sabre ESS9038Q2M chip. Three digital inputs sit at the back - USB type B, coaxial RCA and optical Toslink. The USB port handles PCM to 32 bit and 768 kHz plus DSD64, DSD128 and DSD256 carried as DSD over PCM, whereas Toslink and coax are limited to 24 bit and 192 kHz. A 6.3 mm headphone socket on the front delivers 68 mW into 32 ohm and 6.6 mW into 600 ohm, and a pair of RCA pre outs provides 2.05 V. Pro-Ject quotes 20 Hz to 20 kHz response, 0.0007 percent THD at 0 dB, 2 V RMS and 1 kHz, a dynamic range of 120 dBA and jitter of 100 femtoseconds. The chassis measures 103 x 37 x 122 mm and weighs 360 g without its 5 V, 1 A DC adapter, which comes in the box.

Engineering and use context

The clock circuit is a Pro-Ject design, and all internal oscillators are synchronised to keep timing errors at the quoted femtosecond level. Noise arriving over the USB line passes through two filtering stages before it reaches the converter. The owner can pick one of five digital filter characteristics, and Pro-Ject adds its own optimum transient filter to that list. On the parts side the maker names organic polymer capacitors and thin film miniMELF resistors on a gold plated four layer circuit board. The enclosure is a sandwich of aluminium and metal, chosen to damp vibration and to shield the electronics inside.

Pairing

With its modest current into high loads, the headphone stage suits efficient low impedance headphones rather than planar models or high impedance studio sets. A computer connects by USB for high resolution and DSD files, while a CD transport, streamer or television connects through S/PDIF on coax or Toslink. The RCA pre out lets the box feed a power amplifier or an integrated amplifier line input, so the same converter serves both a desk and a speaker system.

Alternatives

The Pro-Ject Head Box DS3 B is a fully balanced discrete headphone amplifier with RCA and XLR inputs and up to 1500 mW into 32 ohm, but it has no built-in converter.