Unison Research – UNICO 90 – Class-A Hybrid Amplifier

Unison Research – Unico 90 – Class-A Hybrid Integrated Amplifier

The Unico 90 is a hybrid integrated amplifier developed according to specific sonic and scientific criteria set by the design team at Unison Research. These criteria led to a product completely different from anything else Unison Research has ever released. That means it’s also different from every other amplifier, valve or solid state, on the market.

Unison’s research led to two circuit performance standards that are considered essential for excellent performance: a 3-stage circuit and a 2-stage circuit, both with zero global feedback. The first type is used in the new Unico 150, and is more suitable for integrated amplifiers with higher-than average power. The second type, used in the Unico 90, is a more effective application for medium-powered amplifiers.

Both of these approaches allow Unison Research to reach a standard of linearity that is almost impossible with the usual technologies that are matched to single-ended driving capabilities. In fact, the linearity of these new designs is downright remarkable and typical of the best solid state amplification available.

Circuit

The heart of the Unico 90 circuit is found in its hybrid structure. All of the gain, and subsequently the “character” of the amp, is determined by the only tube stage made with ECC83 and ECC81 in particular multiple-parallel-totempole. This stage is made with the six triodes for channel, and is configured so that they present limited gain with the least output impedance possible.

All capacitors touched by the signal are the types that exhibit very low loss and excellent behavior at high frequencies. The polypropylene capacitors in particular, have been widely used for supporting the speed and acceleration of the signal. Three Mundorf capacitors with very low stray inductance are used in each channel to provide a final energy. As usual for Unison Research, these electrolytic caps are constructed from Italian Itelcond and have a low stray inductance, and are doubled on each branch to lower the inductance further.

Power

When designing the Unison Research Unico 90, consistency was one of the primary goals. This consistency is maintained practically at almost every level of power delivery, with the partial exception of the eighth highest at maximum. This is due to the linearity the first two stages of valves, and direct coupling between these and the MOSFET output.

Preamplifier

The preamp section of the Unico 90 also incorporates a number of innovative solutions. The preamp section is totally passive. An ALPS potentiometer is shielded in four sections, parallel in pairs especially in the region of high attenuation. The selected sources are connected one at a time in order to interrupt the ground loops associated to the connections not used.

Switching is performed by purely mechanical miniature relays that are shielded and placed behind the sockets. The terminals of the unused inputs are deflected toward their ground in order to eliminate the risk of capacitive coupling through the movable contacts. The balanced inputs are not obtained by electrical means; instead, Unison used transformers which allow a truly balanced transmission of signals and galvanic isolation.

Construction

The Unico 90 is a dual mono amplifier with a single power transformer capable of delivering 600 VA continuously. The power MOSFET of each channel can handle power up to 900 watts and stationary currents up to ±40A. These circuits, of course, are protected and are weighted on 70% of their maximum specifications so to maintain an adequate margin of safety without affecting driver capabilities.

Speaker Matching

Unico 90 can drive loudspeakers that are very challenging loads, but it is advisable not to choose extreme speakers with a minimum impedance of less than 2 ohms. Its design is based on a balance of features, and altering it would involve sacrifices in certain directions.

Conclusion

Unsion Research has accounted for every detail, and thousands of simulations have been carried out in our research labs to arrive at the Unico 90 integrated amplifier. We have built dozens of prototypes to test every conceivable variation until we have realized our goals through extensive listening tests.