Unison Research Unico 90

Two Stages. Nothing More.

Most amplifiers distort. That's not a controversial claim — it's a physics problem. Every stage added to a circuit introduces its own distortion, and as stages accumulate, the distortion compounds and its structure becomes increasingly complex. The engineering response to this, almost universally, has been to apply global negative feedback — a corrective loop that reduces the audible distortion at the expense of phase accuracy and transient integrity. The result is an amplifier that measures better but often sounds worse than the measurements suggest it should.

Unison Research's answer was structural. Fewer stages. The Unico 90 uses two: a single tube input stage, and a HexFET output stage. That's it. No driver stage between them, no intermediate buffers, no thermal compensation circuit — because the direct coupling between the tube stage and the output stage is linear enough that thermal compensation isn't needed. Zero global feedback. The circuit is correct from the start rather than corrected after the fact.

This is harder to design than it sounds. The single tube stage has to do everything — provide all the gain, establish the tonal character of the amplifier, and present low enough output impedance to drive the HexFET output stage directly. Unison Research achieved it using ECC83 and ECC81 triodes in a multiple-parallel totem pole configuration, six triodes per channel, specifically configured to deliver the required gain with the minimum possible output impedance. Thousands of simulations. Dozens of prototypes. The result is an amplifier that Unison Research describes as achieving a standard of linearity almost impossible with conventional technologies — and that Twittering Machines' Michael Lavorgna described simply as one helluva integrated amplifier.

The Circuit in Detail

The tube input stage runs in pure Class A. The ECC83 handles gain; the ECC81 triodes, wired in parallel totem pole, drive the output stage directly. The signal path from input to output is as short as the two-stage topology allows, and every component in it has been chosen for its behavior at audio frequencies rather than its cost.

Signal-path capacitors are polypropylene throughout — a material chosen for low dielectric loss and fast transient behavior, not just because it measures well but because it sounds right in Unison Research's extended listening tests. Three Mundorf capacitors with very low stray inductance are used per channel as a fast local energy reserve, wired in parallel with the main electrolytic reservoir capacitors to reduce parasitic inductance at the moments when the output stage demands sudden current. The main electrolytic capacitors are Italian Itelcond units, doubled per branch for the same reason.

The preamp section is fully passive — no active gain stage, no op-amp buffer, nothing between the input socket and the tube stage that could add its own character. Balanced XLR inputs use transformers rather than electronic balancing, providing true galvanic isolation and genuine differential signal transmission. Input switching uses mechanical relays mounted directly behind the input sockets, with unused contacts deflected to ground to eliminate capacitive coupling through the switch.

The output stage uses six HexFET devices per channel — three pairs — running at a substantial margin below their maximum ratings. The HexFETs are rated to handle far more current than the Unico 90 will ever ask of them under normal operation, which is not about caution but about the character of devices working well within their limits: more consistent behavior, lower thermal stress, longer service life.

What It Sounds Like

Michael Lavorgna spent over six weeks with the Unico 90, pairing it with the DeVore O/96, the Audiovector QR 7 SE, and the Piega Gen2 411 — three very different speakers in approach and efficiency. It worked well with all three. For the Audiovectors and the Piegas it was his amplifier of choice, lighting them up from bottom to top and making them sound, in his words, their richest boldest bestest. With the O/96 it sang sweetly. His summary: stiff power, agility, and heart, combining to bring music into physical emotive form. Very highly recommended.

NOVO Magazine paired it with the CD Due and found an amplifier that consistently demonstrated the potential of a well-implemented hybrid — the tonal richness of a tube input stage with the current delivery and control of a solid-state output. The dual-mono architecture keeps the channels fully independent from power supply to output, and the audible result is a soundstage stability and channel separation that shared-supply designs at this price rarely match.

The Unico 90 needs a few minutes to sound right. Nominal linearity in seconds; optimal performance in around ten minutes. Not a demanding warm-up ritual, just worth knowing before a critical listening session.

Unico 90 vs Unico 150 — The Right Question

The two-stage circuit of the Unico 90 and the three-stage circuit of the Unico 150 represent Unison Research's two approaches to the same goal, chosen based on power requirements. For the output levels the Unico 90 delivers — 100 watts into 8 ohms, 160 into 4 — the two-stage circuit achieves the linearity target more effectively than three stages would. The Unico 150 uses three stages because the higher power requirement makes two stages insufficient for the gain needed. Neither is a compromise of the other; they are different correct answers to different design briefs.

In practical terms: the Unico 90 is the right choice for most speaker pairings in most rooms, and its two-stage circuit means there is genuinely less in the signal path. The Unico 150 is the right choice when speaker sensitivity, room size, or listening levels demand more headroom. Both sound like Unison Research. Which one is right depends on your speakers.

Press Recognition

Twittering Machines — Michael Lavorgna spent six weeks with the Unico 90 and called it one helluva integrated amplifier, praising its combination of power, agility, and musical heart. Very highly recommended.
Read the review

NOVO Magazine reviewed the Unico 90 alongside the CD Due, finding a consistently convincing hybrid amplifier that made a strong case for Unison Research's approach to combining tube and solid-state technologies.
Read the review

Specifications

• Type — Hybrid integrated amplifier, dual mono, two-stage circuit
• Output power — 100W × 2 @ 8Ω; 160W × 2 @ 4Ω
• Input stage — Pure Class A; ECC83 double triode totem pole + ECC81 parallel totem pole; 6 triodes per channel
• Output stage — Class AB thermostable; 6× HexFET per channel
• Global feedback — 0 dB
• Local feedback — present within output stage only
• Output impedance — less than 0.4Ω (resistive across all audio frequencies)
• Frequency response — -1dB @ 12Hz and 45kHz; -3dB at frequency extremes
• Input impedance — 21kΩ / 300pF
• Input sensitivity — 860mV RMS
• Inputs — 3× RCA unbalanced; 2× XLR balanced (transformer coupled); 1× RCA bypass
• Outputs — 4 + 4 binding posts (bi-wiring); 1× tape RCA; 1× subwoofer RCA (volume controlled)
• Capacitors — Polypropylene signal path; Mundorf fast-reserve per channel; Itelcond electrolytic main reservoir
• Power consumption — 550W at maximum power into 8Ω
• Dimensions — 43.5 × 44 × 18 cm (W × D × H)
• Weight — 20 kg
• Finish — Silver or black
• Origin — Handcrafted in Italy

Questions about how the Unico 90 compares to the Unico 150, or how it pairs with your speakers? We're happy to help you think it through.