Unison Research Triode 25 Black Edition

A Pure Tube Amplifier That Doesn't Ask You to Choose

Most tube amplifiers make you commit. You choose a topology — triode or pentode — and you live with its strengths and its trade-offs. The Triode 25 Black Edition gives you both, switchable from the top panel, and the difference between them is real and audible enough to matter.

In pentode mode the amplifier delivers 50 watts per channel — enough headroom to drive a reasonably wide range of speakers with authority, in a room of moderate size, without strain. The presentation is controlled, relatively neutral, and detailed. There's still the fluidity and tonal coherence that identifies a good tube design, but pentode gives it dynamic grip and composure with complex material. What Hi-Fi described the original Triode 25 in this mode as sounding like a thoroughly modern valve-integrated — controlled, nicely detailed, with the fluidity of tubes coupled to much of the dynamic grip you associate with solid-state alternatives.

Switch to triode and the character changes. Thirty watts, lower output impedance, a more intimate and dimensional presentation. HiFi Pig described a rich liquid silkiness — the kind of sound that makes leading edges crisp and sharp without ever becoming edgy, and that draws you into the music in a way that's hard to describe and easy to recognize. This is the mode for smaller-scale music, for listening sessions where you want the tube character at its most pronounced. It is, as What Hi-Fi put it, a beguiling experience.

Hi-Fi News reviewed the Black Edition specifically and called it a little cracker that outperforms its size and price — a captivating, moreish, and unmistakably tube-like sound that you can leave running at random through analogue or digital inputs without hearing anything disagreeable for hours at a time.

The Black Edition Improvements

The Black Edition is not a cosmetic update to the Triode 25. The circuit has been revised throughout the signal path and power supply, with strategically placed polypropylene capacitors in the power supply and a new input selection circuit borrowed from Unison Research's more premium equipment. Distortion is reduced relative to the standard Triode 25 and power output is increased — the Black Edition delivers more watts in both modes than the original.

The output tubes have changed from EL34 to KT77 Gold Lion. The KT77 is a beam tetrode with characteristics closer to the EL34 than the KT88, but with a somewhat different harmonic structure and a presentation that Unison Research preferred for this specific circuit revision. All signal tubes are Gold Lion throughout — two ECC83 in the input and line stage, one ECC82. These are not stock tubes swapped in for the Black Edition; they are the specified factory complement, voiced as such.

Ground path design and channel separation have received specific attention. The audio signal, where possible, travels in high-quality coaxial cables inside the chassis. The input selection circuit uses micro relays with Return GND technology — the same approach found in Unison Research's reference-tier products — ensuring clean signal routing and minimizing capacitive coupling between unused inputs.

The Built-In DAC

The DAC3 module adds three digital inputs that would otherwise require a separate DAC: USB-B supporting PCM up to 384kHz and native DSD up to DSD256 (DoP to DSD128), plus S/PDIF coaxial and Toslink optical inputs each supporting up to 192kHz. The DAC is built on an ESS Sabre ES9018K2M converter. Digital inputs are not common on pure tube integrated amplifiers — the Black Edition series includes them as standard, which meaningfully expands the amplifier's utility in a modern system without adding an external box.

Bias and Feedback — Owner-Adjustable

The Triode 25 Black Edition has a built-in bias meter on the top panel alongside a trimmer potentiometer, making bias adjustment straightforward for any owner — no multimeter required, no need to send the unit in. The process is simple and safe by design. Feedback is selectable between 10dB and 12dB via a top-panel switch, offering a second layer of character adjustment alongside the triode/pentode mode selection. The lower 10dB feedback setting tends to produce more expressive dynamics and increased fluidity — the setting we'd recommend starting with.

The Aesthetic

The Black Edition name describes a genuine design shift. The wood front panel is finished in piano black, the chassis in gunmetal, with updated lettering graphics. It is a darker, more contemporary look than the standard Triode 25's warm wood tones — the same Italian artisan construction philosophy, a different visual character. The tube cage is black metal, secured with cap screws, and best left off for practical access to the top-panel controls. The four KT77s run warm; ventilation above the amplifier matters.

Speaker Matching

In pentode mode the Triode 25 Black Edition is relatively tolerant of speaker choice. Sensitivities of 87dB and above in small to medium rooms will work well. In triode mode, 30 watts with the output impedance of a transformer-coupled push-pull stage benefits from speakers that are an easy load — 89dB and above, impedance curves that don't dip aggressively. The amplifier is not suited to large rooms or power-hungry speakers in either mode. Within its envelope it is authoritative and tonally convincing. Choose accordingly and it rewards you.

Press Recognition

Hi-Fi News reviewed the Triode 25 Black Edition and called it a little cracker of an integrated amplifier that outperforms its size and price with a captivating, moreish, and unmistakably tube-like sound. The USB DAC was praised as a useful addition, and the pentode/triode switching was noted as serving both system matching and personal taste.
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What Hi-Fi reviewed the original Triode 25 and described pentode mode as controlled, relatively neutral, and nicely detailed, with tube fluidity coupled to solid-state-like dynamic grip. Triode mode was called a beguiling experience — their first choice for small-scale classical and easy-going jazz. Overall verdict: yet another superb design from Unison Research, great to use and even better to listen to.
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HiFi Pig described the Triode 25 as producing a rich liquid silkiness with crisp leading edges and real tonal and dynamic effortlessness — the highest level of polish and refinement from EL34-family tubes they had heard.
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eCoustics noted that the Triode 25 is not warm or syrupy — it does not roll off at the extremes or produce a lush midrange at the expense of everything else. Wonderfully clean and transparent with excellent detail, with just enough tonal color to reveal its valve roots without losing control or organic character.
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Specifications

• Type — Push-pull integrated tube amplifier, Class AB
• Output power — 50W per channel (pentode/ultralinear); 30W per channel (triode)
• Output tube operating mode — Ultralinear with 60% tap (pentode); triode — switchable from top panel
• Signal tubes — 2× ECC83 Gold Lion; 1× ECC82 Gold Lion
• Output tubes — 4× KT77 Gold Lion, push-pull
• Feedback — 10dB or 12dB, selectable
• Bandwidth — 10Hz – 50kHz (-1dB)
• Analog inputs — 3× RCA line
• Digital inputs — 1× USB-B (PCM to 384kHz; DSD256 native; DSD128 DoP); 1× S/PDIF coaxial (to 192kHz); 1× Toslink optical (to 192kHz)
• DAC — ESS Sabre ES9018K2M (DAC3 module)
• Outputs — 1× subwoofer RCA (stereo, unfiltered); 1× line out
• Input selection — Micro relay with Return GND technology
• Bias — User-adjustable via top-panel trimmer and built-in meter
• Dimensions — 30 × 45 × 20 cm (W × D × H)
• Weight — 20 kg
• Finish — Piano black wood panel; gunmetal chassis
• Origin — Handcrafted in Italy

Questions about speaker matching for triode or pentode mode, or how the Triode 25 Black Edition fits into your system? We're happy to help you think it through.