Pro-Ject Uni Box S3 Amplifier Review

When naming the Uni Box S3, Pro-Ject Audio Systems came up with one that describes this compact, bijou streaming amplifier in two distinctly different ways. On the one hand, if all you ever need is a device to enjoy music from your favourite streaming platform, here it is – just add loudspeakers. On the other hand, if you need a control centre for multiple analogue and digital devices, the Uni Box S3 has got you covered comprehensively. You can even stream any of your connected devices to other compatible streamers, such as Pro-Ject’s Stream Box E, Stream Box S3 and Wireless Box E. Clever stuff.

Up Close

At the heart of the unit beats a Class AB integrated amplifier delivering a claimed 23 watts of power at 8 ohms, and 40W into 4. These figures seem a little on the low side, but in practice, there's enough juice on tap to drive most speakers to realistic domestic listening levels – at least in modest-sized rooms. I doubt many users will pair this amp with the huge 15-inch Dual Concentric Tannoy speakers I use, yet this little-and-large combination fills my listening room with ease, my ears giving up the ghost long before the amp runs out of puff. At the other extreme, the Uni Box S3 has no trouble making sweet music with my insensitive (82dB) Rogers LS3/5a mini-monitors. So don’t let its published power figures put you off.

On the streaming side of things, Pro-Ject has shrewdly partnered with WiiM. Employing proprietary WiiM OS technology alongside the dependable Cirrus Logic CS4344 DAC chip, it streams at up to 24-bit/192kHz resolution. You will need to download the Pro-Ject Home app, which offers a multitude of functions, including multi-room use and tone and volume adjustment. On this last point, when streaming, the volume can be adjusted digitally within the app; however, Pro-Ject recommends that for ultimate performance, the digital volume should be set to maximum with the analogue volume pot as the primary volume control. This ensures optimal digital resolution via the lossless analogue volume control, located at the centre of the unit's facia.

Also on the front panel is a 6.3mm headphone socket and a row of LEDs to indicate the chosen source in operation. Two push-buttons let you select the desired connected sources, with a third button dedicated to the streaming function. At the rear of the unit, you'll find an array of analogue and digital connectors. The phono input caters for MM cartridges (as well as high-output MC and moving-iron types), two pairs of line-level RCA inputs, and a pair of variable-output RCA connectors. This analogue variable output enables the connection of a separate power amplifier, active loudspeakers, or even an active subwoofer.

Digital inputs include two TOSLINK optical ports, a coaxial input, and an HDMI ARC input for connecting a TV. A Wi-Fi antenna is included for Bluetooth devices, including BT turntables, while a grounding post for conventional vinyl spinners is also present. Finally, there’s a pair of dinky speaker terminals that accept banana plugs, spade connectors or bare wires, and a connector for the supplied outboard power supply. As you would expect from Pro-Ject, build and finish are excellent for the money, with my review sample in black sporting a lovely brushed aluminium front panel; silver is also available.

For this audition, the Uni Box S3 was used to stream Qobuz, with vinyl replay courtesy of a Garrard 401 fitted with an SME 3009 S2 tonearm tracking a Goldring 1042 cartridge. CD replay was from the similarly sized (the Uni Box measures 206x55x153mm, [WxHxD]) Pro-Ject CD Box E, which I previously reviewed and liked so much that I bought it for my office system.

The Listening

Kicking off with CMAT's Mercury Music Prize-nominated Euro-Country, a densely produced modern pop piece streamed from Qobuz, the Uni Box S3 immediately impresses. It deciphers the multi-layered sounds and stacked vocals with much musical enthusiasm. Clarity and detail are delivered without making the music feel pushed forward. The generous lower registers offer a slight warmth I don't hear through my Naim NAIT XS3. Rhythms are effectively expressed. While the Uni Box S3 isn't as fast-sounding as the Naim, it's agile enough and remains surefooted.

This natural sense of pace and drive serves purely acoustic recordings particularly well. John Coltrane's jazz version of the Mary Poppins soundtrack classic Chim Chim Cheree (Qobuz 24-bit, 96kHz) is played back with fine musical poise in a free-flowing way, never coming across as forced or metronomic. This organic presentation of rhythms allows drummer Elvin Jones' polyrhythms to propel the track convincingly, emphasising the performance's life and vitality.

The classic rock of Led Zeppelin’s II on vinyl sounds as big, bold and beefy through my Tannoy Berkeleys as I'm used to. My original 1969 'plum and orange' Atlantic pressing still outshines the digital remasters that Jimmy Page has overseen more recently, though, more importantly, it confirms that the Uni Box S3's onboard phono stage is no mere afterthought. Pro-Ject acknowledges that many users who go beyond using it as a stand-alone streaming amp will likely choose vinyl as their primary alternative medium.

Despite the heavy, pile-driving rock of Whole Lotta Love, there are moments of relative delicacy that the Uni Box S3 resolves with impressive filigree detail. Cymbals sound lifelike, with wonderful harmonic intricacy and clearly defined transients, while production effects, such as backwards reverb, are not masked or glossed over. The powerful presentation at relatively high volume levels belies this little box’s lowish power rating – in action, the Uni Box S3 has all the power that most will realistically need.

The Verdict

Pro-Ject has covered all the bases with this lovely little streaming amplifier. Sound quality is super for the price, and while it isn’t the last word in transparency, the Uni Box S3 is a fully-featured, fun and engaging device that comes equipped with WiiM’s excellent digital tech. Vinyl replay easily matches and in some cases outperforms hi-res streaming, showing that the internal phono stage is no slouch. Few listeners, I imagine, would feel the need to use an external phono amp. And regardless of source, as long as it’s of sufficient quality, of course, the amplifier does not go out of its way to highlight the flaws in less-than-perfect recordings. This little box’s warm, inviting sound will have you exploring your music collection all over again, and its charming method of music-making is a pleasure at this price.

For more information visit Pro-Ject