Pro-Ject Stereo Box S3 BT

An ultra-compact stereo integrated amplifier with Bluetooth 5.0 aptX HD and two line-level RCA inputs: 2 x 40 W into 4 ohms, motorised analogue volume and a remote handset, for systems where a large amplifier will not fit.

Stereo Box S3 BT: what it offers

Pro-Ject built the Stereo Box S3 BT for situations where space rules out an amplifier of conventional size: it is 103 mm wide and weighs 450 g. Sources connect to two line-level RCA inputs or over Bluetooth 5.0; the receiver handles aptX and aptX HD, the latter with 24-bit signals up to 48 kHz.

Rated power is 21 W per channel into 8 ohms and 40 W into 4 ohms. Volume is analogue, entrusted to a potentiometer turned by a motor: it is set from the knob or from the supplied infrared handset, which also selects the inputs. The variable output on a 3.5 mm stereo jack follows the volume and can feed a subwoofer, active loudspeakers or a second amplifier for another zone.

The RCA sockets are gold plated and the insulated speaker terminals take 4 mm banana plugs, spade lugs or bare wire. The aluminium enclosure is stiff and shields the electronics from vibration and interference. Pro-Ject designs it and builds it by hand in Europe, in a housing no larger than it has to be so as to limit the use of raw materials. The power supply is external.

Specifications

• Type: stereo integrated amplifier with Bluetooth
• Power: 2 x 21 W into 8 ohms, 2 x 40 W into 4 ohms (1% THD)
• Bandwidth: 20 Hz to 20 kHz within 1.5 dB into 4 ohms
• S/N ratio: 96 dB, 100 dB A-weighted, into 4 ohms
• Channel separation: 67 dB measured at 10 kHz
• Distortion: below 0.12% with 5 W into 4 ohms
• Gain: 32.5 dB
• Line inputs: two RCA pairs, 25 kohm impedance
• Variable output: 3.5 mm stereo jack socket
• Speaker terminals: for 4 mm banana plugs, spade lugs or bare wire
• Bluetooth: version 5.0; codecs aptX HD and aptX, A2DP profile
• Power supply: external 20 V / 3 A, mains 100-240 V at 50/60 Hz
• Standby consumption: under 0.5 W
• Remote control: infrared, supplied, takes two AAA cells
• Size (WxHxD): 103 x 37 x 115 mm, 138 mm including sockets
• Weight: 450 g, power supply excluded
• Finishes: black, silver