Thanks to Unison Researchs 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.