Where the Head Box S2 sits in the Pro-Ject range
The Head Box S2 occupies the middle ground of Pro-Ject's dedicated headphone amplifier family, sitting above the entry-level Head Box E and below the fully balanced Head Box DS2 B. It is aimed at listeners who demand more from their headphones than a smartphone or laptop output can provide, offering enough current and voltage swing to drive demanding, high-impedance designs to their full potential without compromise.
Designed around the signal
Pro-Ject has selected only low-noise components throughout the Head Box S2 to ensure the amplification stage adds as little colouration as possible. The result is a measured THD+N figure of just 0.002% and a signal-to-noise ratio of −110 dBV, figures that compare favourably with amplifiers at several times the price. Gain is set at 11 dB, providing enough lift for sensitive in-ear monitors as well as harder-to-drive circumaural headphones, without adding unwanted noise to the signal path.
Practical connectivity
Two headphone outputs are fitted on the front panel: a 6.35 mm quarter-inch jack for traditional hi-fi headphones and a 3.5 mm jack for modern portable designs, including earphones. Both outputs can be used simultaneously for shared listening. A bypass RCA loop output on the rear allows the Head Box S2 to be inserted into an existing system without disrupting the main signal path, feeding a secondary amplifier or recording device while headphone monitoring continues. A single RCA input accepts any analogue source.
Build quality and power
The enclosure is machined from aluminium with an aluminium and metal sandwich construction. This approach shields the internal circuitry against electromagnetic interference and isolates it from vibration, both of which can introduce audible artefacts into a sensitive headphone amplifier. The compact 103 mm wide footprint suits desktop use alongside a turntable, streamer, or DAC. Power is supplied externally via a 5 V DC adaptor; an optional Accu Box S2 or Accu Box S2 USB battery supply is available for those who wish to eliminate any mains-borne interference entirely.
