Unison Research Unico Due

A Complete System Hub with a Tube Heart

The Unico Due occupies a particular position in the Unison Research line: it is the most feature-complete integrated amplifier in the range, the one you buy when you want the tube-driven character of the Unico circuit philosophy alongside a built-in DAC, an integrated phono stage, and enough connectivity to anchor a full system without additional boxes. It was also the first Unico to introduce the BJT super-symmetric output stage architecture — a meaningfully different approach from the HexFET designs used in the Unico 90 and 150, and one chosen specifically to lower distortion in the output stage to the point where it stops competing with the character of the tube preamp section.

That last point is the design brief in a single sentence. Unison Research's stated goal for the Due was to create an amplifier whose sonic character is dominated by the valve section. Everything in the output stage was engineered to stay out of the way of the tube stage's voice. It is, by their own description, why they bothered minimizing solid-state distortion in an amplifier that has a tube preamp adding its own small amount of distortion in the first place. The tube character is what they wanted you to hear. The solid-state output stage is what makes that character audible through any speaker you connect.

The Power Supply — Ten Regulated Supplies

The Unico Due's power supply is the part of the design that most clearly signals the level of engineering ambition. Ten separately regulated power supplies — output voltages ranging from 15V for low-signal operational amplifiers up to 300V for the valve preamp stage. This is not a conventional approach. Most amplifiers at this price use a single power supply, possibly two. Ten regulators add cost, complexity, and PCB real estate. Unison Research used them because each section of the circuit benefits from its own regulated supply with appropriate voltage and current characteristics, and because common-mode interference between circuit sections is reduced when they don't share a supply rail.

The main power transformer is shielded and encapsulated — chosen for reduced electromagnetic interference rather than minimum cost. Filter capacitance was substantially increased relative to the preceding design. Nearly 25% of the total PCB surface area across all boards in the Due is dedicated to powering the output devices. The supply tracks on those boards are 105-micron copper — three times standard thickness — and the ground return paths were designed with the same care as the signal paths. This is the kind of power supply engineering that shows up in the sound as a lower noise floor, tighter bass, and more consistent behavior across the full dynamic range.

The Output Stage — Super-Symmetric BJT

The output stage uses bipolar junction transistors in a super-symmetric configuration — positive and negative signal polarities handled separately by complementary N and P type devices. The goal is cancellation of even-order harmonic distortion at the output stage, which is the type of distortion that solid-state output stages most commonly generate and the type that most readily obscures the tonal character of the tube input stage upstream.

Dynamic Class A biasing keeps current flowing through the output transistors even at very low signal levels — preventing the output stage from switching off and back on during quiet passages, which is the source of the crossover distortion that Class AB designs can exhibit at low volume. At the listening levels where most people actually spend their time, the Due behaves like a Class A amplifier. At higher levels, it transitions to Class AB to maintain efficiency and control heat. The bias circuit monitors and adjusts continuously, without the listener ever hearing the transition.

Large-value capacitor banks are placed physically close to the power transistors to minimize the impedance of the current path during high-demand transients. Three-ounce copper PCB tracks handle the current delivery. Microprocessor-controlled protection reduces output level rather than cutting off abruptly if the amplifier is pushed too hard for too long.

The Tube Preamp Stage

One ECC83 double triode per channel, operating as a gain stage with a cathode-follower driving the power stage directly. The specific ECC83 types were selected by listening tests rather than specification comparison — a process Hi-Fi News noted as the only sensible way to choose them. The tube stage is kept powered in the OSB standby mode, allowing rapid readiness without a full cold start, and the DAC output in that mode can be used independently — as a standalone DAC output direct to a headphone amplifier or other downstream component — while the power stage remains in standby.

The Built-In DAC

The ESS Sabre ES9018K2M DAC handles USB input with a jitter eliminator circuit, supporting PCM up to 32-bit/384kHz and DSD up to DSD256. The USB input is USB-B, for connection to a computer or dedicated music server. The DAC output feeds both the preamp and a dedicated line output — the latter allowing the Due to function as a standalone DAC, bypassing the amplifier entirely when needed. For a system built around a computer audio source, this eliminates the need for a separate DAC entirely.

The Phono Stage

The integrated phono stage is configured for Moving Magnet cartridges as standard. A service engineer can reconfigure it for Moving Coil cartridges. For listeners with a single turntable and an MM cartridge, the built-in stage removes one more box from the equipment rack and one more set of interconnects from the signal path.

Connectivity

• 3× RCA line inputs (one configurable as phono MM)
• 1× USB-B digital input (Sabre ES9018K2M DAC; PCM to 384kHz/32-bit; DSD256)
• 1× RCA AV bypass input
• Tape loop (record out / monitor in)
• Subwoofer output (low impedance, stereo RCA)
• DAC line output (independent of power stage)
• 4 + 4 binding posts per channel for bi-wiring
• Gold-plated input and speaker sockets
• Gold-plated valve holders
• Mundorf capacitors in signal path
• Remote control included

Press Recognition

Hi-Fi News reviewed the Unico Due in depth, covering the power supply architecture, the super-symmetric output stage design, and the tube preamp selection process in detail. Their assessment of the circuit engineering was positive throughout, noting the ten regulated power supplies and the unusual level of care applied to the output stage power distribution as distinguishing features at this price point.
Read the review

Audio Affair praised the Due's ability to bring all the benefits of valve technology without the typical shortcomings, and noted that its big-hearted sonic presentation — with enough power for large orchestral works alongside the delicacy for vocal and chamber music — makes it an amplifier that rewards long-term ownership.
Read the review

Specifications

• Type — Hybrid integrated amplifier
• Output power — 100W × 2 @ 8Ω; 180W × 2 @ 4Ω; 290W × 2 @ 2Ω
• Preamp stage — Class A; 1× ECC83 double triode per channel; cathode-follower output
• Output stage — Dynamic Class A biased BJT; super-symmetric complementary N/P configuration
• Power supply — 10× separately regulated supplies (15V to 300V); shielded encapsulated transformer; 105µm PCB tracks
• DAC — ESS Sabre ES9018K2M; USB-B input; PCM to 384kHz/32-bit; DSD256; jitter eliminator
• Phono — MM standard; MC by service modification
• Analog inputs — 3× RCA line (1× configurable as phono); 1× RCA AV bypass
• Digital inputs — 1× USB-B
• Outputs — 4 + 4 binding posts (bi-wiring); subwoofer RCA (stereo, low impedance); DAC line output; tape out
• Connectors — Gold-plated throughout, including valve holders
• Capacitors — Mundorf in signal path
• Protection — Microprocessor-controlled output level limiting
• Standby — OSB mode keeps tube stage and DAC active; power stage in standby
• Finish — Silver or black
• Origin — Handcrafted in Italy

Questions about how the Unico Due compares to the Unico 90, or whether the built-in DAC and phono cover your source needs? We're happy to help you work through it.