Unison Research S6 Black Edition: our test

Unison Research S6 Class A integrated valve amplifier

From Unison Research, an Italian brand of great tradition and recognized quality, we had tested some time ago the Simply 845 model being very satisfied with it.
During the last Monaco High End, the brand managers had shown us the internal components of the Unison Research S6 Black Edition model that today we have the pleasure of testing.
This is the evolution of a model, the S6 precisely, which has been present in the catalog of the Venetian manufacturer for many years and that over time has undergone some significant revisions while remaining faithful to the original setting.

S6 Black Edition: Dark Elegance and Excellent Performance

The Unison Research S6 Black Edition presents itself as a stylistic evolution of the famous S6 tube amplifier, enhanced by a new black look that gives it a sleek and modern appearance.
Interestingly, the natural wood tones of the “basic” version have given way to a different finish while continuing to use the same material for the front panel.
Designed for audiophiles who seek not only sonic excellence but also refined design, this special edition enters the mid-to-high end of integrated tube amplifiers, developing and bringing to fruition the sonic characteristics that have made the S6 a benchmark.
With its 40 watts per channel in Class A, the Black Edition will appeal to those who desire a warm, musical and enveloping sound, enhanced by a contemporary aesthetic.

Technical Analysis

The Unison Research S6 Black Edition does not deviate from the technical layout of the standard model, however, the revision of some technical details allowed for a significant performance improvement.
Most notably, the circuits have been revised in the signal path and power supply management.
In place of the six EL34 tubes we now find fine KT77 Gold Lion tubes, again in parallel single-ended configuration.
The polarization of the power amplifier tubes has been completely revised to eliminate the capacitor and cathode resistor.
The preamplifier section is entrusted to two dual ECC83 triodes also sourced from Gold Lion. The amplifier is of the Dual Mono type and operates entirely in Class A and without feedback in the first stage.
Compared with the S6 “Standard” model, the Black Edition has eliminated the semi-automatic adjustment of the rest current of the tubes ( bias).
Tale regolazione è ora completamente manuale e viene portata a termine mediante l’ausilio dei due strumenti circolari – uno per canale – e un gruppo di tre interruttori/trimmer.
Questo, assieme alla rivisitazione del layout delle schede di potenza, ha consentito un incremento di potenza passando dai precedenti 35W a 40 W unitamente ad un miglioramento del rapporto segnale/rumore.

Another area in which improvements have been made is in the input stage and its selector switch.
The use of micro relays with gold-plated silver contacts ensures stable contact over time and avoids crosstalk with other unselected sources connected to the amplifier.
The return grounds of the inputs have been implemented with technology Return GND, capable of providing an individual, short-length path for each input. In addition to four unbalanced line-level inputs (RCAs), the Unison Research S6 Black Edition has a digital section with USB input (PCM up to 384kHz, native DSD up to 256x and DoP up to 128x), Tos-link and SPDIF (up to 192kHz as per standard) that report to a DAC based on the Sabre ES9018K2M chipset.
From signal the unfiltered connection for a subwoofer.
Speaker connectors are of excellent quality, and the output is optimized for a 6-ohm load.

For those who would like to know more about the technical solutions implemented in this amplifier, we point out the interview with designer Alessio Fusaro that we conducted in May 2024 at the Monaco High End.

Listening and Conclusions on the Unison Research S6 Black Edition

The listening experience offered by theUnison Research S6 Black Edition is confirmed to be top-notch, reproducing a richly detailed and well-balanced soundstage.
The tube system gives the sound a warm and smooth signature, with excellent mid and high frequencies.
Singers, in particular, come across as expressive and engaging, with a naturalness that we have experienced with few other amplifiers, regardless of their price range.
The bass, while not as deep and impactful as in some solid-state realizations, is well controlled and articulate, confirming its excellence especially in genres such as jazz and classical music.
Overall dynamics are convincing, and even in the most complex musical passages, the S6 Black Edition manages to maintain cohesion and transparency, returning every nuance with precision and fluidity.
Even high volumes, the amplifier shows no signs of compression or fatigue.

TheUnison Research S6 Black Edition is an excellent choice perfect audiophiles who desire not only top-notch sound performance, but also an exclusive and modern design.
The warm and engaging sound, typical of tube amplifiers, is enhanced by elegant aesthetics.
The tonal quality, combined with the solid construction and refined finish, makes this amplifier an ideal solution for those seeking excellence, both aesthetically and functionally.

Technical specifications.