Unison Research Preludio Integrated Amplifier

Unison Research was founded in 1987 by a group of passionate audiophiles led by Giovanni Maria Sacchetti. After completing his studies in electronics, Giovanni devoted twenty-five years to teaching while at the same time designing and developing amplifiers for Unison Research, including the legendary Simply Two, achieving great international success in a relatively short time. Designed and produced to high performance and quality standards entirely in Italy, Unison Research is now recognised as the Italian leader in the production of tube amplifiers, and among the top ten in Europe.
Part of our classic line of tube amplifiers that include the Sinfonia and the Performance, the Preludio integrated amplifier continues the technical approach, sound and aesthetics of its larger siblings. While the Preludio’s appearance is certainly gorgeous, it is also extremely reliable due to its unique design solutions, quality materials and adherence to the highest of standards.

UNISON RESEARCH PRELUDIO WHITE PAPER
To complete the series of all-tube integrated amplifiers, including successful models like Performance and Sinfonia, Unison Research introduces the new Preludio.
This new amplifier, though maintaining the distinctive technical elements, sound characteristics and winning look of the preceding models, features original solutions which are the result of Unison Research design and production experience gained over the years.
Like the other models of the same series, and faithful to a consolidated Unison tradition, the Preludio is an integrated amplifier.
Integration offers several advantages, both in terms of simplicity of use and attainable sound quality: an integrated amplifier requires less cabling than its separate counterparts thus allowing a substantial reduction of the effect of cable impedance on timbre and dynamics, and a significant saving in production costs as well.
On the other hand, designing an integrated amplifier is much more critical and challenging than designing a separate pre-power combination: let us mention, for example, how carefully all the possible interferences between different components and different stages (power supply, control, preamplification and output stage) have to be considered and limited.
Our experience in the design and production of integrated amplifiers has grown over the years, allowing us to create successful products which are today valuable classics, like the widely renowned Absolute 845.
The Preludio, though small in size, reaches an output power of 14-15W per channel.
As the Performance and the Sinfonia, the Preludio is characterized by the presence of two large heatsinks mounted on the sides, which are required by the high voltage stabilized power supply circuits, and by a wide stainless steel cover. The cover material is magnetic and has low thermal conductivity: it has been chosen to prevent the heat generated by the two KT88 from reaching the circuits located below, thus improving the stability, the sound quality and the overall reliability of the system.
The power supply of the Preludio is based on a single toroidal transformer, especially designed to minimize the magnetic flux dispersion.
In an audio amplifier, the anodic voltage should ideally be supplied by a battery, but this is obviously not possible for a number of reasons: high costs, short life-expectancy, large size and weight, etc.
We considered this problem in depth, in the attempt to obtain a power supply stage whose electrical characteristics were the closest possible to those of a battery bank. We found an excellent compromise with a special anodic power supply circuit which features an output capacitance much higher than usual.
As far as concerning the amplification circuit, each channel of the Preludio is constituted by a preamplification stage, a power stage and a dedicated output transformer.
Preamplification and power stage drive are based on a double triode ECC82. This valve guarantees excellent linearity and nearly complete absence of odd order harmonic distortion components.
Each amplification stage is entrusted exclusively to valves, and all operate in pure Class A.
Since the beginning, Unison Research has been directly involved in designing, developing and building the output transformers for its devices. We feel that valve amplifiers performances are closely connected to the quality of these complex components. Thanks to a particular elaboration of the output transformers it has been possible to design for the Preludio a power stage constituted by a single KT88 per channel in single-ended ultra linear configuration, in which the KT88 (beam power tetrode) operates with good approximation like an ideal triode.
The current needed by the ECC82's heaters is supplied, as in the Sinfonia, by cathode current of the 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 and the 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 volume using the remote IR handset. The analogue volume regulation is operated by a high quality ALPS RK27 stereo motorized potentiometer.
Close to the "tape out" output connector, a low impedance output terminal has been added to allow the connection to an active sub-woofer. This output line is connected through the volume potentiometer to the selected input, so it replicates the actual signal present at the preamplification stage. A buffer circuit based on operational amplifiers has been added to increase the impedance seen by the signal sources.
The output terminals are constituted by two plated universal connectors per channel, allowing the connection of 6 Ohm nominal impedance loudspeakers.
In Preludio nothing has been left to chance: from the choice of components, the control knobs and the wood parts, to the design of the chassis and the circuit's boards.
Control knobs are machined from solid magnetic stainless steel. Thanks to their weight, mass and balance, 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 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 Preludio 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 dimension, distribution and lay out of the PCBs have been accurately studied and optimized to limit electrical disturbances and prevent components overheating.

Type: Integrated Valve Amplifier
Valve Complement: 2 x KT88, 2 x ECC82
Operating Mode: Pure Class A
Power stage: Single-ended ultralinear
Output Power: 14 Watt/channel
Bandwidth: 20 Hz - 85 kHz (- 1 dB @ 7 W)
Load Impedance: 6 Ohm
Input Impedance: 47 kOhm
Inputs: 4 line, 1 tape
Outputs: 1 tape, 1 subwoofer (active)
Power Consumption: 200 VA max
Dimensions : 400 (W) x 380 (D) x 200 (H) mm
Weight: 18.0 kg

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