Pro-Ject Head Box S2
Compact headphone amplifier from Pro-Ject, fitted with an RCA input and two simultaneous jack outputs, designed to get the best out of demanding hifi headphones.
Description
The Head Box S2 is a headphone amplifier from Pro-Ject, designed to compensate for the lack of power from the audio outputs of laptops and smartphones. Placed between an analogue source and one or more headphones, it provides the energy needed to fully exploit the potential of hifi headphones that are demanding in terms of impedance or sensitivity.
The unit delivers 725 mW of power into 32 ohms, with a gain of 11 dB. The signal-to-noise ratio reaches -110 dBV and total harmonic distortion plus noise (THD+N) remains below 0.002%, values that reflect a clean signal with little electronic interference. Crosstalk of 68 dB limits interference between the left and right channels, favouring a precise stereo image. The frequency response extends from 20 Hz to 80 kHz (± 0.2 dB), well beyond the range of human hearing, leaving a comfortable margin across the entire usable band.
The chassis is made entirely of aluminium, a choice intended to protect the circuit against electromagnetic interference and mechanical vibration that could degrade the signal. The unit features a stereo RCA analogue input, an RCA passthrough output for chaining to another device, and two headphone outputs: a 6.35 mm jack for hifi headphones and a 3.5 mm mini-jack for more common headphones and earphones. Both outputs can operate simultaneously, allowing shared listening between two people.
This type of amplifier is aimed at those using demanding hifi headphones, whether at a desk or in a small living-room setup, who wish to pair them with an existing analogue source rather than the limited headphone output of a consumer device. Its compact format and separate power supply make it easy to fit into a workspace or a system dedicated to headphone listening.
Technical specifications
| Power | 725 mW (into 32 ohms) |
| Signal to noise ratio | -110 dBV |
| Total harmonic distortion + noise (THD+N) | < 0.002% |
| Gain | 11 dB |
| Crosstalk | 68 dB |
| Frequency response | 20 Hz - 80 kHz (± 0.2 dB) |
| Dimensions (H × W × D) | 37 x 103 x 120 mm |
| Weight | 365 g |
| Connections | 1x stereo RCA/Cinch analogue input, 1x stereo RCA/Cinch analogue output (passthrough), 1x 6.35 mm jack headphone output, 1x 3.5 mm mini-jack headphone output |
What to check before buying used
The volume potentiometer deserves testing across its full range: crackling or a balance that drifts at low settings indicates wear on the resistive tracks, common on headphone amplifiers that have already seen use. Also check that both headphone outputs (6.35 mm jack and 3.5 mm mini-jack) make good contact, as they can become oxidised through repeated insertion, and confirm there is no background noise or hum once the unit has warmed up, which would point to ageing capacitors.
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