For the purposes of the acoustic evaluation, the I/50 replaced the reference amplifiers (Melos Plus Series Line/Parasound HCA3500) and undertook to drive the reference loudspeakers (ATC SCM-50PSL). As a source, for the greater part of the listening sessions, the reference DAC (Teac Esoteric D70) was employed via a single-ended connection, with the WiiM Pro streamer and the Teac Esoteric P70 CD transport serving as the front end.
The initial installation of the amplifier did not present any problems. It goes without saying that the tubes generate significant amounts of heat, and this must be taken into account. The evaluation process was preceded by a trial to determine which output tap should be used. With the particular loudspeakers and in our listening room, it quickly became evident that the 4Ω tap allowed the amplifier to operate with greater ease, especially with regard to dynamics. On this basis, the entirety of the listening sessions was carried out using this connection.
The first impression one derives upon listening to the I/50 is that of a disciplined character and very low noise. The system, with the Audio Research as the system's amp, sounded detailed, with a well-structured soundstage, convincing depth, and a very good rendering of motion, while at the same time proving highly capable in describing dynamic contrast. With regard to the first characteristic, the probable reason lies in the carefully matched power tubes (as can also be seen in the inter-channel differences during response measurements), while the second should be attributed to the meticulous construction quality.
From the very first hours of our contact with the I/50, its capabilities in terms of driving power and output level also became apparent: this is an amplifier with sufficient power to cover a small or, at most, medium-sized room, provided the loudspeakers have “normal” sensitivity. Furthermore (as was evident from the measurements), the variation of the loudspeaker’s impedance modulus proves more critical than its minimum value (since the latter can, to a great extent, be compensated for by selecting the appropriate tap). This means that there exist loudspeakers that the I/50 will not favor, and this is something that requires attention. That said, although the SCM-50 would not be the first loudspeaker one would recommend for such an amplifier, the final outcome of their matching was genuinely impressive on many levels, as the amplifier appeared to take full advantage of the analysis capacity offered by this particular loudspeaker.

To the details, the system, with the I/50, extended comfortably to the very low frequency part of the spectrum and reproduced the relevant material with good volume and control, filling the room impressively and creating a sense of ease. The tube character made its presence clear here, not so much through a distinctive signature or tonal coloration, but rather through the way overload manifests itself, as the power stage approaches its limits. The listening experience always remained ear-friendly, devoid of harshness or aggressiveness. One could allow the amplifier to operate around and slightly above its threshold of overload without discomfort, and the I/50 proved to be one of the most enjoyable amplifiers we have reviewed in recent years.
The lows were presented effortlessly, with a sense of balance and speed, exhibiting good impulse and a very good impression of size scale. When required by the recording, the system sounded large and uncompressed, with the rhythm flowing naturally and percussion sounding full without exaggeration or restriction. Ultimately, the I/50 sounds large, an attribute that should assuredly be counted among its strengths.
The midrange is certainly one of the device’s strongest assets (together with the stereo imaging, as we shall see below). The system acquired a notably positive and clear presence, never receding, maintaining its distance from the listener, and sounding pleasantly warm and balanced with excellent capacity for detail and layering. The presentation felt natural and effortless, with the choir and solo voices revealed in the space in a quite different manner relative to the reference preamplifier/power amplifier combination, perhaps less studio-like, but certainly more alluring, pleasant, and relaxing. If the I/50 possesses a personality, this remark best describes it, and I believe this is the aspect of the amplifier that most listeners will cherish. I also suspect that it is precisely in this domain that “the hand of Audio Research” and the tradition created through Warren Gehl’s tuning—the individual responsible for the sonic character of every device of the company in Minnesota—becomes evident.
The stereo image created by the small Audio Research amp is exemplary. The horizontal axis remains close to the listener, who gains an especially precise sense of the mix. The soundstage possesses depth and an excellent sense of air and motion, and the focusing of individual sound sources is also of the highest order. One assumes that inter-channel uniformity and the tracking of the attenuator play their role, but, in the overall picture, the exceptionally low noise certainly contributes, allowing the outstanding rendering of the macro-dynamic profile of each track. In moments of silence, where the slightest detail, fixed in space, can make the difference, the I/50 proved itself outstanding.
Towards the high frequency band, the amplifier sounded sufficiently fast, with a good sense of extension, full-bodied, and with strong capabilities in rendering details. It accurately conveys the harmonic richness of instruments in this range and, naturally, will never cause fatigue, regardless of the demands placed upon it. This, too, is one of the advantages of tube technology, and it would be unthinkable for Audio Research not to exploit it to the fullest extent.

Conclusion

Although I am aware that many will be satisfied simply with the fact that we are speaking of a genuine and, comparatively, affordable Audio Research product, the truth lies much deeper: here we are, dealing with an exceptional specimen of a tube amplifier, with all the advantages and uniqueness of the kind, as realized by a legendary company. An attractive, effortless, precise, and relaxing sound that honors one’s music collection, a modern aesthetic approach that retains the codes of tube design, but—at the same time—an instrument that requires some attention in its matching with the rest of the system. If one pays close attention to the choice of loudspeakers connected to its output, what we have is technological poetry. By all means, listen to it.

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