Integrated amplifiers — Pro-Ject Uni Box S3

The Uni Box S3 by Pro-Ject of Austria is a compact integrated amplifier that includes a network streamer running the WiiM OS platform. Beside the streaming section, it provides analogue line connections, MM phono, several digital inputs and a headphone amplifier. Its pre and power amplifier sections are fully analogue, housed in an aluminium case offered in black or silver, and it can be used entirely without a mobile app. Analogue sources such as turntables are not digitised on their way to the speakers.

Key specs that matter

Output is 2 x 23 W into 8 ohms and 2 x 40 W into 4 ohms at 1% THD, from a Texas Instruments TPA3221DDV power amplifier chip. Distortion is under 0.05% at 10 W into 4 ohms, a 94 dB signal to noise figure applies at 4 ohms, and channel separation is -67 dB at 10 kHz. Across 20 Hz to 20 kHz, response varies by 0.4 to 0.9 dB into 4 ohms. Conversion is handled by a Cirrus Logic CS4344 DAC working at up to 24 bit and 192 kHz. The case measures 206 x 55 x 153 mm, or 176 mm deep with sockets, and has a weight of 1,100 g, not counting the adapter.

Engineering and use context

Network playback runs over dual-band Wi-Fi 5 (802.11 b/g/n/ac on 2.4 and 5 GHz), and Bluetooth 5.0 supports SBC and AAC. Wired digital connections are one coaxial RCA input, two Toslink optical inputs and an ARC input for a television. Analogue sources connect through a pair of stereo RCA line connections plus an MM phono socket. A pair of RCA sockets provides a variable output for a subwoofer or an external amplifier. The headphone amplifier supplies 70 mW into 32 ohms at 1% THD. Loudspeakers attach via 4 mm plugs, spades or plain wire ends. An external supply delivers 20 V at 3 A DC from 100 to 240 V mains at 50 or 60 Hz, and standby consumption is less than 0.5 W.

Pairing

The ARC input lets a TV send its audio to the amplifier over HDMI, and the Pro-Ject Home app detects the unit automatically and guides the network setup, with a front-panel button for resetting Wi-Fi. Connected sources such as a turntable, CD player or TV can also be streamed on to other compatible streamers. One pair of passive loudspeakers can serve both music and television. An MM turntable needs no extra preamplifier, and the variable RCA output can drive an active subwoofer that tracks the main volume.

Alternatives

Pro-Ject also builds the Stereo Box DS3, an integrated amplifier with 80 W per channel into 8 ohms, Bluetooth and phono support for MM and MC cartridges.