Three amplifiers symbolize the success of Unison Research: the Simply Two, the Triode 20 and the legendary Absolute. On the occasion of the 25th anniversary of the birth of Unison Research, we pay homage to these historic devices by offering the Simply Two and the Absolute in a limited and numbered “Anniversary” edition. We’ve also decided to offer a completely new version of the Triode 20 and named it, quite appropriately, the Triode 25.

The Triode 25, like its predecessor, is a push-pull amplifier that utilizes EL34 tubes in the output stage. The push-pull circuit includes a final stage with two power tubes intended for the amplification of the positive half-waves, respectively, and of the negative half-waves of the audio signal. The task of properly reconstructing the audio signal is then assigned to the output transformer which, thanks to its symmetrical structure, allows for a highly linear signal. Here are some of the more important and significant benefits of a push-pull structure in this type of amplifier design:

– Higher output power
– Higher efficiency and therefore less heat generated, with positive effects on the durability of the output tubes as well as a significant savings in energy costs
– No static polarization of the output transformer, resulting in better performance of this section

To ensure high quality sound in an amplifier with a push-pull configuration, however, it is essential that all individual amplification stages, especially the two semi-output amplifiers, are carefully designed and constructed to prevent the formation of dangerous and compromising odd-order harmonic distortion. This is even truer for the output transformer.

The new Triode amplifier 25 has experienced a long and painstaking design and testing period despite the considerable experience already gained in the construction of its predecessor, the Triode 20. The Triode 25 can operate in two modes: triode and pentode. The latter is capable of delivering a maximum power output of over 45 watts per channel with a load of 6 ohms with harmonic distortion extremely contained across the entire audio band.


  • Output Stage: Push-pull, ultralinear, Class-AB
  • Output Power: Approx. 45 watt per channel
    Pentode configuration
    Approx. 25 watt per channel
    Triode configuration
  • Output Impedance: 6 Ohm
  • Input Impedance: 47 kOhm / 50 pF
  • Negative feedback: 5 dB or 1.8 dB
  • Valve complement: 2 x ECC83 (12AX7) 1 x ECC82 (12AU7) 4 x EL34 (6CA7)
  • Power Consumption: 300 watt max
  • Fuses: T6.3A from 100V to 130V T3.15A from 220V to 250V
  • Dimensions: 30 cm x 45 cm x H. 20cm
  • Net weight : 20 Kg


Italian manufacturer Unison Research marks its 25th anniversary with three new products: special editions of the Simply Two and Absolute 845 (arguably the company’s most iconic products to date), as well as a homage to its first integrated amplifier, the Triode 20.

But don’t let this fool you, the Triode 25 is no throwback. It’s a thoroughly modern valve-integrated amplifier with some interesting features. You can even buy a version with a built-in DAC (for an extra £150), although our review sample isn’t so equipped. On the surface, this line-level integrated amplifier is little different from much of the valve-based competition, featuring as it does, a preamp section with a pair of ECC83 valves and a quartet of EL34s to drive the speakers.

Yet, have a closer look, and Unison Research delivers a number of interesting twists to the established formula.

The Triode 25 can be switched from Pentode to Triode mode at the flick of a switch, even while you’re listening to music.  Pentode and Triode refers to the configuration the output valves work in – and switching between the two settings gives a distinct change of character to the 25. In Pentode mode, the power output is 45 watts per channel.

This gives the amplifier enough grip to work well with a relatively wide range of speakers, though we still wouldn’t necessarily partner this integrated with something insensitive in a large room.

But most sensibly selected speakers, in a small to medium-sized room (say less than 25sq m), can be driven to decent, if not quite head-banging, levels.

In this configuration, this Unison Research sounds controlled, relatively neutral and nicely detailed. There’s still the fluidity that people associate with valve products but here it’s coupled to much of the dynamic grip transistor-based alternatives are capable of.


Unison Research’s track record with sensibly priced valve amplifiers is second to none. The Triode 25 is yet another strong performer that marries fine sound and distinctive aesthetics with pleasing build.

If you value subtlety and finesse above all else, there are few better alternatives at this price.                             READ MORE