Интегральные усилители — Pro-Ject Stereo Box S3 BT

The Stereo Box S3 BT by Austrian brand Pro-Ject is a very small integrated amplifier in a rigid aluminium case, combining two analogue line inputs with Bluetooth reception. It is part of the S3 generation of the Box Design range, is handmade in Europe and is offered in a black or silver version. Pro-Ject states that the housing is only as big as necessary in order to save raw materials, and aims for a device built to last.

Key specs that matter

Rated output is 2 x 21 W into 8 ohms and 2 x 40 W into 4 ohms at 1% THD. Distortion is below 0.12% at 5 W into 4 ohms. Noise performance is 96 dB, or 100 dB A-weighted, at 4 ohms. Channel separation is -67 dB at 10 kHz. Frequency response across 20 Hz to 20 kHz deviates by less than -1.5 dB into 4 ohms. Gain is 32.5 dB, and the line inputs present 25 kOhm input impedance. The case measures 103 x 37 x 115 mm, growing to 138 mm in depth with sockets, and it weighs 450 g excluding the mains adapter.

Engineering and use context

The two pairs of RCA line inputs take analogue sources such as a CD player, a streamer or an external phono preamplifier. Bluetooth 5.0 with aptX, aptX HD and the A2DP profile lets a phone or tablet play wirelessly. Level is adjusted by a motor-driven analogue volume control, which also responds to the infrared remote supplied with the unit, powered by two AAA 1.5 V batteries. A 3.5 mm stereo jack carries a variable line output, so a powered sub or another amplifier can follow the volume setting. Speaker terminals accept 4 mm bananas, spades or bare cable. Power arrives from an external 20 V, 3 A DC supply that runs on 100 to 240 V mains at 50 or 60 Hz, and the amplifier draws less than 0.5 W in standby. The rear panel therefore carries only the two RCA input pairs, the jack output, the speaker terminals and the power socket, and Pro-Ject presents the unit as an answer to setups where a large amplifier cannot be used.

Pairing

At a width of just over 10 cm, the amplifier fits beside a computer or on a narrow shelf, and it can drive a pair of compact passive loudspeakers. Because it has no phono input of its own, a turntable needs a separate phono stage connected to one of the line inputs. The variable jack output can feed an active subwoofer.

Alternatives

For a unit with digital inputs and a built-in phono input, Pro-Ject offers the Stereo Box E integrated amplifier with optical and coaxial S/PDIF connections.