Unison Research Preludio White Paper - VMAX Services

Since the beginning, Unison Research has been directly involved in designing, developing andbuilding the output transformers for its devices. We feel that valve amplifiers performances areclosely connected to the quality of these complex components. Thanks to a particular elaboration ofthe output transformers it has been possible to design for the PRELUDIO a power stage constitutedby a single KT88 per channel in single-ended ultra linear configuration, in which the KT88 (beampower tetrode) operates with good approximation like an ideal triode.The curent needed by the ECC82’s heaters is supplied, as in the SINFONIA, by cathode current ofthe KT88 tubes, the regulation of the voltage is guaranteed by a dedicated stabilized power supply.This interesting solution uses part of the power that is usually wasted in cathode power resistors,this increases the efficiency of the amplifier, lets us optimise the dimensions of the components andthe design of the layout, and improves the reliability of the system.The PRELUDIO has a microprocessor-based circuit which allows the user to control the volumeusing the remote IR handset. The analogue volume regulation is operated by a high quality ALPSRK27 stereo motorized potentiometer.Close to the “tape out” output connector, a low impedance output terminal has been added to alowthe connection to an active sub woofer. This output line is connected through the volumepotentiometer to the selected input, so it replicates the actual signal present at the preamplificationstage. A buffer circuit based on operational amplifiers has been added to increase the impedanceseen by the signal sources.The output terminals are constituted by two plated universal connectors per channel, allowing theconnection of 6 Ohm nominal impedance loudspeakers.In PRELUDIO nothing has been left to chance: from the choice of components, the control knobsand the wood parts, to the design of the chassis and thecircuit’sboards.Control knobs are machined from solid amagnetic stainless steel. Thanks to their weight, mass andbalance, they provide smooth and precise control when operated manually.The wood parts, besides the visual appearance function, also play another carefully calculated role:they contribute to damp out induced resonance in the metal chassis. Thanks to this structuraldamping 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 longterm musical quality, all the components used in the PRELUDIO have been chosen with care: fromthe non inductive resistors and the filter capacitors, to the pure ceramic valve bases and thevetronite printed boards.The dimension, distribution and lay out of the PCBs have been accurately studied and optimized tolimit electrical disturbances and prevent components overheating.TECHNICAL CHARACTERISTICSType:Valves complement:Operating mode:Power stage:Output power:Output impedance:Input impedance:Inputs:Outputs:Power consumption:Dimensions:valve integrated amplifier2 x KT88, 2 x ECC82pure Class Asingle-ended ultra linear14 W per channel6 ohm47 Kohm4 line, 1 tape1 tape150 W max380 x 200 x 400 mm15 x 8 x 15.75 inches