Streamers — Pro-Ject BT Box S2 HD

The BT Box S2 HD is a Bluetooth 5.0 receiver, described by Pro-Ject Audio Systems as its next-generation high-definition model, which turns a phone, tablet or laptop into a wireless source for an existing hi-fi system. It supports the aptX HD codec alongside standard aptX and SBC, and adds both an analogue RCA output and an optical Toslink output. Production is done by hand in Europe, and the housing comes in a choice of silver or black.

Key specs that matter

Bluetooth reception follows the A2DP profile on the 2402 to 2480 MHz band, with a receiver sensitivity of -88 dBm and an effective working range of up to 10 m when nothing blocks the path. The nominal analogue output level is 2 Vrms. Frequency response runs from 20 Hz to 20 kHz within 1.5 dB, signal-to-noise ratio on the line output is better than 85 dB, and THD on that output stays below 0.1%. Through the optical connection THD drops to under 0.003%. The case measures 116 x 37 x 103 mm, or 108 mm deep including the sockets, and has a mass of 320 g, not counting the power adapter.

Engineering and use context

The design relies on the higher range and transmission bandwidth of Bluetooth 5, using aptX HD to avoid the lossy compression artefacts of simpler codecs. According to the maker, aptX HD holds the stream together even when connection quality drops for a moment. Behind the digital section sits a dedicated analogue output buffer stage intended to drive the connection to an amplifier with a stable signal. Pairing is automatic and takes 3 to 5 seconds, and the box stores up to 8 different Bluetooth source devices, so several family members can reconnect without repeating the setup. An external antenna is supplied in the box. Power comes from an outboard 5 V, 1000 mA DC supply rated for 100 to 240 V mains at 50 or 60 Hz, and the unit itself draws 200 mA DC.

Pairing

The RCA stereo output connects to any free line-level input of an integrated amplifier, preamplifier or pair of active speakers. The optical S/PDIF output, where distortion is lowest, lets the receiver feed a separate converter or the digital input on an amplifier instead, bypassing the internal analogue stage. Because the box matches the footprint of other Pro-Ject Box components, it can sit in a stack with them on one shelf. Phones and computers that support aptX HD transmit at the higher resolution, while other devices fall back to aptX or SBC automatically.

Alternatives

For network streaming instead of Bluetooth, Pro-Ject offers the Stream Box E.