Pro-Ject Head Box S3 B
Headphone amplifier from Pro-Ject with a fully balanced signal chain, featuring four headphone outputs and compatible with both balanced and unbalanced headphones.
Description
The Head Box S3 B is a headphone amplifier from the Pro-Ject brand, designed to complement a hi-fi source or a desktop system. It receives a signal via RCA or XLR inputs and delivers it to a pair of headphones, with the distinctive feature of offering a fully balanced signal chain from input to output.
This balanced architecture applies to both the RCA and XLR inputs and the headphone outputs: the Pentaconn 4.4 mm and 4-pin XLR connectors accommodate balanced headphones, while the 3.5 mm and 6.3 mm outputs remain available for conventional unbalanced headphones. The power delivered varies according to the impedance of the connected headphones, from 480 mW at 8 ohms up to 820 mW at 32 ohms, with a further 320 mW available at 300 ohms, allowing it to drive both sensitive headphones and more demanding models. A signal-to-noise ratio above 115 dB and harmonic distortion below 0.002% at 1 kHz demonstrate close attention to signal cleanliness, while crosstalk kept below -81 dB at 10 kHz ensures good channel separation, a particularly sensitive point in a balanced configuration.
This type of device is aimed at listeners who already own a quality pair of headphones, balanced or not, and who wish to get the most out of them from a conventional hi-fi source or an external DAC. The presence of an RCA loop output also allows the unit to be chained to an amplifier or active speakers, making it a central component in a mixed headphone and speaker set-up.
Technical specifications
| Maximum output power | 480 mW / 8 ohms, 680 mW / 16 ohms, 820 mW / 32 ohms, 320 mW / 300 ohms |
| Headphone output | Balanced 3.5 mm, 6.3 mm and 4.4 mm connectors, balanced 4-pin XLR |
| SNR | > 115 dB “A” weighted at 1 kHz |
| THD | < 0.002% at 1 kHz at 500 mV input |
| Crosstalk | < -81 dB at 10 kHz |
| Gain | 15 dB / 9 dB (RCA input / XLR input) |
| Frequency response | < -0.25 dB at 20 Hz-20 kHz |
| Analogue inputs | 1 pair RCA/Cinch, 1 pair XLR |
| Analogue loop outputs | 1 pair RCA |
| Headphone impedance | min. 8 ohms |
| Power supply | 18 V/1 A DC, 110-240 V, 50/60 Hz |
| Standby power consumption | < 0.5 W |
| Dimensions (W x H x D) | 206 x 55 x 15 |
What to check before buying used
Check that each headphone output works correctly (3.5 mm, 6.3 mm, Pentaconn 4.4 mm and 4-pin XLR), as a rarely used connector may have an oxidised or intermittent contact. Also test the RCA and XLR inputs at the rear, as well as the volume knob, which can develop crackling if the potentiometer is worn. The original external 18 V power supply must be present, as an unsuitable generic unit could degrade the stated performance.
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