Forty-five centimeters long, nearly seven kilos on the scale, a varnished wooden cabinet and a solid aluminum front panel. The Primus lives up to its Latin name (“the first”): it sits in the middle of the Sonoro range, between the Prestige model with a CD player and compact radios like the Stream. The German manufacturer from Neuss has concentrated the essence of its audio expertise here in a format that can replace a complete hi-fi system, minus the optical drive.
The Primus is not a simple radio sitting on a shelf. Its acoustic system combines two coaxial drivers (a 19 mm tweeter centered on a 76 mm midrange) with a 133 mm subwoofer installed under the chassis, facing the floor. This “downfire” configuration uses the space between the cabinet and the surface it rests on to disperse the bass. The bass-reflex port, also located on the underside, completes this setup.
Five Class D amplifiers deliver a total power of 80 watts RMS: 2 × 20 W for the tweeters, 2 × 20 W for the midrange drivers, and 40 W for the bass. A digital signal processor (DSP) manages frequency distribution and powers several predefined equalization profiles (Pop, Rock, Jazz, Classical, Flat). The entire system performs satisfactorily in rooms of up to around 25 m².
The “3D Sound” mode deserves a closer look. Activated from the menu, it widens the soundstage by creating a sense of space that goes beyond the physical boundaries of the cabinet. The effect doesn’t turn the Primus into a separate stereo system, but it does add an appreciable spatial dimension, particularly with classical music and acoustic recordings.
The Primus centralizes virtually all the audio sources you could want. The built-in tuner receives FM and digital radio DAB/DAB+. Via Wi‑Fi, it has access to more than 25,000 Internet radio stations and podcasts. Spotify Connect, Amazon Music, and Deezer are directly integrated into the interface (earlier versions, referenced SO-410-XXX, also offered Qobuz, Tidal, and Napster).
On the back, the connectivity includes a 3.5 mm jack auxiliary input, an RCA line input (to connect a turntable with a preamp, an external CD player, or any other analog source), an optical digital input (practical for connecting a TV), an RCA line output (for connecting an additional subwoofer or an external amplifier), and a USB port limited to charging on current versions.
The front headphone jack offers wired individual listening. The bidirectional Bluetooth, based on Qualcomm aptX technology, not only allows the Primus to receive music from a smartphone, but also to send sound to wireless headphones. This feature is still uncommon on radios in this category.
Sonoro provides three control modes. On the aluminum front panel, a notched rotary knob adjusts the volume and navigates through the menus displayed on the 2.8-inch color TFT screen. Programmable direct selection buttons give instant access to favorite stations or services. This is often the fastest method for everyday use.
The supplied remote control reproduces these functions at a distance. It runs on a CR2032 button cell battery. The OKTIV mobile app (available on iOS and Android for recent SO-3400-XXX versions) offers full control from a smartphone: switching between sources, station search, favorites management, sound settings. Its response time may feel a bit slow for users used to quickly scrolling through large music libraries, but assigning favorite stations to the shortcut buttons on the device itself works around this limitation.
Older models (SO-3400-100- and SO-410-XXX) use the UNDOK app instead of OKTIV.
The wooden cabinet, hand-sanded according to Sonoro, receives several coats of varnish. The rounded corners, a visual signature of the brand, soften the lines. The front panel and controls are made of solid aluminum, with finishes available in matte black, gloss white, matte graphite, champagne, or matte white depending on the series. The unit weighs around 6.7 kg, which gives it appreciable stability.
The TFT screen features a polarizing filter and automatic dimming that adjusts brightness to ambient light. An alarm function is built in, allowing you to wake up to the radio or a classic alarm tone.
This attention to manufacturing quality has earned the Primus the 2021 Red Dot Design Award and the Plus X Award in the design, quality, and functionality categories.
The optical digital input (Toslink) can receive sound from a TV equipped with an optical audio output. The Primus then serves as an audio system for television, with the option to adjust the sound via the built-in equalizer.
In standard receive mode, the Primus plays music sent from a smartphone or tablet via aptX Bluetooth. In transmit mode, it can send sound to a wireless Bluetooth headphone, which is handy for nighttime listening without disturbing others in the room.
Recent versions (product number starting with SO-3400-XXX, except SO-3400-100-) use the OKTIV app, available on iOS and Android. Older versions use the UNDOK app.
The RCA line output on the back allows you to connect an additional subwoofer or link the Primus to an external amplifier. The built-in 133 mm subwoofer remains active.
The Meisterstück is larger (57 cm wide versus 45 cm), heavier (around 9 kg), and has a built-in CD player. Its midrange and tweeter drivers are separate, whereas the Primus uses coaxial drivers. The Meisterstück is better suited to larger rooms, up to around 35 m².
Sébastien
Good product, but the sound is a bit too heavy on the bass. I’ve reduced it almost to the minimum; I was expecting better sound…
Comment from January 20, 2026 — Experience from January 09, 2026
Thomas
It's hard to find a more compact system while maintaining audiophile-grade sound quality.
Ideal for providing sound in a small room like a bedroom or kitchen.
Ability to play any digital music format in a user-friendly way thanks to the app.
Plus, the finish is very clean and the unit looks great on a nice piece of furniture!
Comment from April 11, 2024 — Experience from March 30, 2024
