Pro-Ject Head Box DS3 B silver

Pro-Ject Head Box DS3 B: fully balanced headphone amplifier

Properly driving a high-end headphone requires amplification capable of delivering voltage and current without coloring the signal or clipping on dynamic peaks. With this first model in a new generation of the Box Design range, Pro-Ject applies the balanced principle from one end of the chain to the other, from the XLR or RCA inputs to the balanced headphone outputs. The fully aluminum enclosure and European manufacturing complete a specification focused on performance.

An end-to-end balanced signal chain

Balanced amplification is regularly advertised by manufacturers, but is often limited to the output connector. Pro-Ject says it wanted to avoid this shortcut on the DS3 B: the two inputs (RCA and XLR) feed a fully balanced chain all the way to the corresponding headphone outputs. The amplifier design is fully discrete, with no integrated operational amplifier in the audio path.

As for the measurements published by the manufacturer, the signal-to-noise ratio exceeds 118 dB A-weighted at 1 kHz, total harmonic distortion remains below 0.002% (at 1 kHz for 500 mV at the input), and crosstalk is specified below -83 dB at 10 kHz. The frequency response does not deviate by more than 0.2 dB between 20 Hz and 20 kHz.

Power reserve for demanding headphones

The power stage delivers up to 1500 mW into 32 Ω in balanced mode. Into 8 Ω, it provides 510 mW; into 16 Ω, 900 mW; into 300 Ω, 560 mW. This distribution covers both low-sensitivity planar magnetic headphones (often current-hungry) and high-impedance dynamic models from the studio world (which require voltage). The minimum accepted headphone impedance goes down to 8 Ω, opening the door to certain low-impedance in-ear monitors without risk to the amplifier’s stability.

Gain is differentiated depending on the input: 12 dB from the RCA input, 6 dB from the XLR input. This asymmetry takes into account the fact that a balanced source generally delivers double the level of its unbalanced counterpart; the gain difference compensates to maintain comparable volume from one source to the other.

Four headphone outputs and two source inputs

Four headphone outputs are wired on the front panel. Balanced: one 4.4 mm Pentaconn connector and one 4-pin XLR socket. Unbalanced: one 3.5 mm jack and one 6.3 mm jack. This combination covers the terminations supplied with most current headphones, from the classic studio jack to the Pentaconn that has become common on recent high-end models.

At the rear, one pair of RCA inputs and one pair of XLR inputs allow two sources to be connected simultaneously, switched by a selector on the front panel. An RCA loop output repeats the RCA input signal without amplification, making it possible to coexist with an integrated amplifier or active speakers on the same source.

Aluminum chassis and external power supply

The enclosure is entirely made of aluminum, including the buttons and knob. This construction serves two purposes: electromagnetic shielding for the low-voltage stages (which are sensitive to radiated interference) and a weight of 1430 g excluding the power supply, which limits vibrations transmitted to the components. The dimensions of 206 × 70 × 194 mm (218 mm with the rear connectors) make integration easy on a desk or in a compact hi-fi rack.

The power supply is external, provided as an 18 V / 1 A DC adapter, compatible with 110-240 V at 50 or 60 Hz. Separating the transformer from the audio circuits prevents radiation from the adapter from polluting sensitive stages; standby power consumption remains below 0.5 W. Manufacturing takes place in Europe, in continuity with the rest of the Box Design range. Two finishes are available: silver or black.

Integration into a hi-fi system

The DS3 B connects to the output of a DAC, a preamplifier, or directly to a source with a line output (network player, variable output of a converter, CD player). The two parallel inputs make it easier to use multiple sources together, and the RCA loop output allows simultaneous connection to a speaker system without having to reconnect the DAC for each listening session. On a desk, the compact format and front-panel connectors make everyday use convenient; in a hi-fi rack, the DS3 B fits alongside a preamplifier or DAC from the same range.

Technical specifications

Architecture and design

• Fully symmetrical and discrete topology, a reference in its category
• Discrete amplifier design for maximum performance
• Masterfully refined symmetrical architecture
• Fully symmetrical signal path for RCA and XLR inputs

Audio performance

• Maximum output power
  • 510 mW at 8 Ω
  • 900 mW at 16 Ω
  • 1500 mW at 32 Ω
  • 560 mW at 300 Ω
• Signal-to-noise ratio: > 118 dB A-weighted at 1 kHz
• Total harmonic distortion (THD): < 0.002% at 1 kHz for a 500 mV input
• Crosstalk: < -83 dB at 10 kHz
• Gain: 12 dB / 6 dB (RCA input / XLR input)
• Frequency response: < -0.2 dB from 20 Hz to 20 kHz

Connectivity

• Analog inputs: 1 pair RCA / Cinch, 1 pair XLR
• Analog loop outputs: 1 pair RCA (pass-through output for additional amplifier)
• Balanced headphone outputs: 4.4 mm Pentaconn, 4-pin XLR
• Unbalanced headphone outputs: 3.5 mm, 6.3 mm
• Headphone impedance: 8 Ω minimum

Power supply

• Power supply: 18 V / 1 A DC, 110-240 V, 50 / 60 Hz
• Standby power consumption: < 0.5 W

Chassis and finish

• Full aluminum chassis providing robust mechanical protection and effective shielding against electromagnetic interference
• High-quality aluminum controls and buttons
• Available finishes: silver, black

Dimensions and weight

• Dimensions (w × h × d): 206 × 70 × 194 (218) mm
• Weight: 1430 g without power supply