Inspired by the highly acclaimed Performance amplifier, the Sinfonia is designed to be as close to the appearance and technical ability of the Performance while achieving a lower price-point. By making this an integrated design Unison Research have stayed true to their traditions, supporting the philosophy that integrated amplifiers can achieve a better sound by taking away the need for external cables, as cable impedances can negatively effect the timbre and dynamics of a hi-fi system's delivery.The Sinfonia is a dual-mono design, which effectively eliminates the possibility of cross-channel electrical interference. Each amplification stage inside the Sinfonia is pure Class A and operates exclusively with valves. The amplifier is able to deliver a very capable 27-30W (max.) output power, per channel.The Sinfonia, like the Performance, is accented by two large heat-sink "wings" mounted on the sides. These are required by the high voltage stabilized power supply circuits, which are protected by a wide stainless steel cover. The top-plate is non-magnetic stainless steel and has low thermal conductivity, so it prevents the heat generated by the four KT88 from reaching the circuits located inside. This improves the stability of the amplifier, which in turn enhances the sound quality and the overall reliability of the system.
Thanks to Unison Research's extensive knowledge of output transformer production, the Sinfonia has been designed with a power stage that is made up of two KT88 valves per-channel in single-ended parallel ultra-linear configuration, in which the KT88 (beam power tetrodes) operate, with good approximation, like an ideal triode. This configuration provides very good results in terms of sound quality, however the natural drawbacks of valves (namely the non-uniform decline in performance over time due to drift) need to be addressed. So, after much testing, Unison Research developed an an original circuit design which, through the control of the KT88 bias, ensures a real-time compensation of the parameters affected by drift. This solution guarantees the best sound quality even after many years, and also contributes to a slight reduction in the time it normally takes for the tubes to warm up after switching on and reach the optimal temperature.The pre-amplification and the power stage drive are based on the double triodes ECC83 and ECC82. These valves guarantee excellent linearity and offer a nearly complete absence of odd-order harmonic distortion components. Both the stages are made up of triodes in parallel and are biased by automatic bias circuits. In this way the output impedance of the two circuits can be slightly reduced, which in turn improves the linearity of the stages. The signal-to-noise ratio and the total harmonic distortion improve significantly in this design as well. The direct current on the preamplifier valve filaments is supplied by an interesting circuit configuration: it works by directing the power stage valves cathode current through a parallel regulator which operates like a zener diode to the filament’s terminal.With audio amplifiers, the anodic voltage should ideally be supplied by a battery, but this is obviously not possible for a number of practical reasons. So, to compensate, the Sinfonia employs a special anodic power supply circuit that features an output capacitance that is much higher than usual, emulating the performance of a battery supply.The appearance of Sinfonia is both striking and functional. The control knobs are machined from solid, non-magnetic stainless steel and are weighted and balanced to provide a smooth, precise performance when used. The wooden parts, aside from their obvious visual beauty, effectively dampen out induced resonance in the metal chassis. Thanks to this structural damping, the valves themselves, which like all vacuum tube devices are susceptible to microphony, are much less liable to generate unwanted resonance-related effects. For the best reliability and long term musical quality, all the components used in the Sinfonia have been chosen with care from the non-inductive resistors and the filter capacitors, to the pure ceramic valve bases and the vetronite printed boards. The dimensions, distribution and lay out of the PCBs have been accurately studied and optimized to limit electrical disturbances and prevent components from overheating.The supplied infra-red remote handset allows for convenient control over input switching and the premium motorised volume pot from ALPS. The back panel is finished with six gold-plated speaker terminal connectors that allow the connection of 4Ω and 8Ω loudspeakers, alongside clearly marked gold-plated RCA inputs for multiple audio sources. Next to the "Tape Out" connector is an additional low-impedance output terminal for connecting an active subwoofer; this terminal is linked to the pre-amplifier stage directly for reliable sub-performance. The source inputs have a buffer-stage to eliminate any negative effects connecting a subwoofer could have on the performance of the amplifier. The back-panel also has a power cable connector for upgrading the basic power supply included with the Simply Phono phono stage.
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