Усилители для наушников — Pro-Ject Head Box S3 B

The Head Box S3 B is a fully balanced headphone amplifier from Pro-Ject Audio Systems, placed in the S3 generation of the compact Box Design range. It accepts line signals through RCA or XLR and drives both balanced and single-ended headphones, and it is built in Europe in a full aluminium case that is sold in silver and in black.

Key specs that matter

Rated output rises from 480 mW into 8 ohm to 680 mW into 16 ohm and 820 mW into 32 ohm, and 320 mW remains available into 300 ohm. The lowest headphone impedance Pro-Ject allows is 8 ohm. Gain is 15 dB from the RCA input and 9 dB from the XLR input. Signal to noise is stated as better than 115 dB A-weighted at 1 kHz, THD under 0.002 percent at 1 kHz with 500 mV input, crosstalk better than minus 81 dB at 10 kHz and a response within 0.25 dB from 20 Hz to 20 kHz. Four headphone sockets are fitted - 3.5 mm and 6.3 mm single-ended, 4.4 mm Pentaconn balanced and 4-pin XLR balanced. An 18 V, 1 A DC supply rated for 110 to 240 V at 50 or 60 Hz powers the unit, and standby draw is below 0.5 W. The case is 206 x 55 x 153 mm, 170 mm deep with feet, and weighs 950 g without the adapter.

Engineering and use context

Pro-Ject keeps the signal path balanced from input to output for both the RCA and the XLR connection, so an unbalanced source is still carried through a balanced chain. The stated aim of this topology is maximum separation between channels and a low noise floor. The aluminium enclosure provides mechanical stiffness and also acts as shielding against interference. A pair of RCA loop outputs passes the incoming analogue signal on to other equipment, which lets the amplifier sit between a source and a speaker system without losing an input on the main amplifier. The lower XLR gain reflects the higher level that balanced sources usually deliver.

Pairing

Balanced headphone cables use the two balanced outputs, while ordinary headphones use the single-ended jacks. The power reserve into high loads suits many high impedance dynamic headphones, and the low minimum load covers low impedance planar models. Any converter or network player fitted with XLR sockets makes full use of the balanced input, and the loop output can feed an integrated amplifier.

Alternatives

The Pro-Ject Head Box DS3 B uses a discrete fully balanced circuit with the same socket layout and rises to 1500 mW into 32 ohm and 560 mW into 300 ohm.