Unison Research S6 Mk II Integrated Valve Amplifier

UNISON RESEARCH S6 Mk II, Single-Ended Parallel, Ultralinear Class 'A' Stereo Integrated Valve Amplifier.


[Finish: Cherry, Black]



Description

After many years of great success we have decided to propose a new updated and improved version of ‘S6.
In this new model, the configuration of the final stage was maintained with a Parallel Single Ended Ultra-Pure Class A. The polarization of individual tubes has been changed and transformed from fully automatic to mixed.

About 2 / 3 Bias is obtained with a cathode- type auto polarization and a third from the fixed polarization.
The fixed polarization of each valve is adjustable through a potentiometer and an illuminated analog instrument (for each channel).
The choice of the mixed polarization increases the efficiency of the final stage and reduces the factor of local feedback with an appreciable improvement in sound.

The output transformer is a new design and has a fixed output impedance of 6 ohms.
As is known the nominal impedance declared for an acoustic diffuser is not very significant: the real impedance undergoes significant changes with frequency, and its value may even drop below the nominal value stated. In this regard it should be noted that all the speakers produced by Unison an Opera are in accordance with DIN specifications and never drops below the minimum values indicated by that rules (20% of the nominal value).

The decision to standardize the output impedance to 6 ohms is aimed at optimally interface all speaker with nominal impedance of 4 or 8 ohms.

Particular attention was paid to the power stage: each preamp stage is decoupled and filtered separately.
The new S6 has also been redesigned from the mechanical point of view: the two channels of the amplifier no longer share a single printed circuit but are now separated in two circuits located on the right and left of the chassis. This solution has greatly improved both the crosstalk and the heat dissipation. In this way the temperature in the various circuits is more controlled in the interest of sound quality, stability, reliability and the very life of electronic components.

The S6 aesthetic has been totally renovated giving to the amplifier greater personality and refinement. In particular, the new front panel, with inlaid wood in contrast, shows the amplifier technology and highlights the unique “Made In Italy” taste.

The latest version of the Unison Research S6 integrated amplifier is the result of over 25 years of experience with building valve amplifiers that have been praised all over the world for their beauty, reliability and performance. Our main goal with the S6 was to create an EL-34 integrated amplifier that has compact dimensions yet is able to drive most speakers comfortably—even those designs with relatively low efficiency.

The S6 uses three EL-34 tubes in the output stage per channel, connected together in a triple-parallel configuration that operates in single-ended Class A ultralinear mode. With this design, the S6 is able to supply an ample 35 watts per channel. Both 4-ohm and 8-ohm speaker outputs are available so that you can match the loudspeaker of your choice to the S6 for the best results.

The S6 was also designed with simplicity in mind. Our designs ensure that a minimum amount of components are found in the signal path, because we believe that the finest sound quality is the result of an unimpeded signal flow. This simplicity also translates to an amplifier that is more reliable and trouble-free in its operation.

Our dedication to robust and reliable products extends to the design of our transformers. Unison Research is one of the few audio companies in existence that designs and builds its own output transformers—each and every one is built by hand in our own workshops. We carefully match the size of each transformer to match the circuit—nothing is taken “off the rack.” This approach ensures the S6 will have a very wide frequency response, tube life will be extended and that this amp will last and produce beautiful music for decades.

The extraordinary beauty of the S6’s exterior is practical as well. Unison Research is known for its gorgeous wood accents, and the chassis of the S6 is no exception. These wood accents, however, assist in reducing vibrations that can affect the signal path. The control knobs are machined with precision from stainless steel to extremely tight tolerances—we do this for both accuracy and for the wonderful tactile qualities of these surfaces. Finally, we have designed stainless steel baseplates for the tube sockets that act as thermionic reflectors and excel at dissipating heat from the amplifier. This feature is not only visually stunning; it also extends the life of your S6 amplifier.

We spent countless hours perfecting the S6, and the result is an amplifier that epitomizes the Unison Research sound—warm, airy and transparent. From its Italian craftsmanship to its ingenious circuit design, we think you’ll agree that the S6 is one of our greatest achievements.