Unico Due is the latest amplifier from Unison Research.
Unico Due benefits from Unison Research’s decades of experience in design and production technology.
It maintains all the best qualities that made its predecessor a runaway success and introduces new and enhanced features.
Circuit
The electronic circuitry of the Unico Due has been completely redesigned.
While maintaining the qualities that made the Unico range such a legend in the audio industry, key improvements
have been made that are nothing short of ground-breaking.
Firstly, the power supply circuits have been enhanced thanks to a substantial increase in filter capacitance size
and to a new high quality shielded and encapsulated power transformer.
The new power distribution system of the audio power output stage combines space optimization, superior circuit
solutions and improved assembly and service solutions.
The heart of the preamplifier stage in based around two ECC83 double triodes (one per channel), configured as a
gain stage followed by a cathode-follower.
This circuit’s low output impedance efficiently drives the power stage that follows.
The final choice of the type of valve and the circuitry used was made following extensive listening tests, after we
experimented many equally high performance valve-based solutions and configurations in our test laboratory.
Features
The Unico Due aims to satisfy even the most demanding users and offers the following features:
Three line inputs, of which one can be configured to become a phono input after easy installation of an
internal phono stage module which can accept any type of turntable cartridge
One USB input to the Unico Due’s internal DSD 128 bit DAC
One direct analogue line output from the Unico Due’s internal DAC, which allows it to be used as a stand-alone DAC
A low impedance subwoofer output (SUB) with variable output level from the preamp for connection to an active subwoofer
AV input that allows the Unico Due to be connected to a home theatre system: pressing the “push” button on
remote control, the Unico Due will automatically select the chosen channel at a user-configured volume level
Dynamic Class A power amplifier biasing where the power transistors never turn off completely
This provides excellent sound results even at low volume
The Unico Due offers four inputs: three analogue inputs and one USB digital input.
The input selection uses sealed miniature relay switches to preserve the delicate low-level signals,
whereas the volume regulation is based on an integrated high-precision, high-performance resistor
array followed by a set of digitally controllable analogue switches, used in reference products and
capable of 120 dB of attenuation with 0.5dB steps.
The power output stages are solid state and use a completely original combination of bipolar and
MOSFET transistors.
Furthermore, instead of designing in standard differential input stages, a sophisticated symmetrical
BJT circuit is used that has moderate gain and very high intrinsic linearity, with separate feedback
loops for AC and DC signals.
Thanks to its low distortion, we were able to configure it to have a very mild feedback level.
The power output stages of the Unico Due feature a non-switching bias control circuit which prevents
the current in the output transistors to reach zero.
This greatly reduces distortion at low and very low listening levels and guarantees the highest sound
transparency in any condition.
The power output devices are connected in a “super symmetrical” configuration, i.e. negative and
positive signal polarities are handled separately by a combination of N and P type devices.
You may ask yourself why we should worry about minimizing the distortion of the solid state power output
stages when there is a valve pre-amplifier section that will add a small amount of distortion.
The reason is very simple: our goal was to create an integrated amplifier whose “sonic character” was
mainly dominated by the valve section, but with enough power to comfortably drive any loudspeaker system.
To improve performance further, we added regulated power supplies not only when it was absolutely necessary,
but also in any part of the circuit where this would bring sonic improvements over using simple filtering.
In the Unico Due there are no less than ten stabilized power supplies with output voltages ranging from
15V for low signal operational amplifiers to the 300V required by the valves in the preamplifier stage.
Particular attention was paid to the output power stage supply.
Considering the high value, impulsive, almost intractable nature of the current that the power stage has
to handle, we decided to adopt a bold solution.
We used large-value, high-quality capacitor banks, some of which are placed close to the power transistors
to minimize the path to the current pulses.
The supply tracks on the PCB are generously sized, having a thickness of 105um (3oz), and the ground
return tracks have been designed with extreme care.
Obviously difficult choices like these can create a number of design and realization difficulties which many
engineers may decide to give up on and find easier solutions, but the engineers at Unison Research embraced
these challenges and solved them without compromising on quality and performance.
The final result is a design where almost 25% of the entire surface of all the PCBs in the Unico Due is dedicated
to supplying power to the output devices!
The same meticulous attention was paid to managing the low-level audio signal.
Starting with the gold-plated input connectors, to the speaker sockets that are also gold-plated, robust,
versatile and completely insulated according to the latest regulations.
Furthermore, the audio signal is fed through circuitry using the highest available quality of components:
high-precision sealed micro-relay switches, carefully selected Mundorf capacitors, low tolerance metal
film resistors, ceramic tube sockets with gold contacts, and much more.
Specifications
Output power: 100W RMS on 8ohm 200W RMS on 4ohm
Frequency response: flat @ 10Hz- 0.5dB @ 100kHz
Input impedance: 50kohm // 47pF
Input sensitivity: 375mV
Input stage: Pure A Class, Double tube stage ECC83/12AX7
Output stage: Dynamic A Class double POWER MOSFET complementary pair
Damping factor: >50 on 8ohm
Feedback factor: 8dB
THD: <0.5% @ 1kHz, 100W in 8ohm
Inputs:
4 Line RCA
1 Phono RC
1 Line Balanced
1 USB
Line Outputs: 1 tape, 1 sub (volume controlled)
Outputs connectors: 4 + 4 bi-wiring
Power consumption: 400W max
Dimensions (H x W x D): 13 x 43.5 x 43 cm
Weight: 15 kg
Colors: black, silver