Unison Research – Triode 25 – Ultralinear Class-A/B Integrated Amplifier

Unison Research – Triode 25 – Ultralinear Class-A/B Integrated Amplifier

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. Unison 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.

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“If I were in the market for a valve amplifier then this would probably be the one I would buy.  I listened very hard for any fuzziness, harshness, noise, distortion, ringing, muffling, or veiling and I found none.  Sure, the bass lacked concussion-inducing power but I could live with that, as what was there was clean with no trace of bloom or boom, which does annoy the heck out of me.  On the positive side it has a sweet beguiling sound that you can listen to for many hours and not once will it displease you in sound terms.”  — HiFi Pig Magazine, February 2017 (full review here)

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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 45W per channel with a load of 6 ohms with harmonic distortion extremely contained across the entire audio band.