Tube Power Amp Reviews

When the VS110 was returned to me, I checked the bias voltages, and all were spot-on. More important, the right channel no longer had a high noise level, and, as far as I could tell, sounded the same as the left. The VS110 was problem-free for the rest of the review period. The SP16L functioned flawlessly at all times.

Sound
A principle long recognized in audiophile circles is that a given component's contribution to the sound of a system depends not only on the component's overall sound quality (ie, the extent to which it's transparent to the signal), but also on the way it interacts with other components in the system. Component A may sound terrific in System X but not in System Y; Component B may not work well in System X but may sound just right in System Y. The presence of this type of interaction doesn't necessarily make it impossible to evaluate components—but it certainly complicates the reviewer's life!

Early on in my evaluation of the sound of the new Audio Research components, it became obvious that I was going to have to pay more than usual attention to the matter of component interactions. I began by introducing the VS110 into the system, using my long-term reference CAT SL-1 Ultimate preamp and Avantgarde Uno 3.0 speakers.

The last power amplifier I'd had for review was the Audiopax Model Eighty-Eight (Stereophile, May 2003), a tube amplifier of unusual design that sounds quite wonderful with the Avantgardes—unfailingly musical in its harmonic balance, and minimizing harshness and distortion in the source. My only criticisms of the Audiopax were that high-level dynamics were a little muted, with some effect on the music's pace, and bass extension was not the best I've heard with these speakers.

As it turned out, the most immediately obvious differences on changing over to the VS110 were in dynamics and bass extension. The VS110 has 100W compared to the Audiopax's 25W, which is a substantial difference, but the Avantgarde's sensitivity is over 100dB, so one would think that anything beyond a handful of watts would represent overkill. Still, the difference was there.

While the VS110's tonal character did not resemble that of a solid-state amplifier, its dynamic authority with the Avantgardes recalled high-powered solid-state amps like the big Krells or Brystons, and its bass extension similarly resembled its solid-state brethren. "Exciting," "taut," "crisp," "dynamic," and "fast" were some of the adjectives that occurred to me to characterize the sound of the VS110. Large-scale orchestral pieces, such as the Russian sonic spectaculars on Vodka & Caviar (Delos DS-3288), played at a realistic level (in this case, loud) were simply...well...spectacular.

However, an area of sonic performance where the Audiopax was still superior was in the natural quality of harmonic textures: the famed "magic" midrange quality that's the traditional domain of single-ended triode amplifiers. (The Audiopax is actually a single-ended pentode, but with what's called Perfect Triode Stimulation.) A friend who is very familiar with the sound of my system and who has a superb system of his own (Sound-Lab A speakers, Jeff Rowland Design Group amplifiers, TacT 2.0 preamp/room-correction unit), said that he felt the Audiopax amp had a more "lovely" sound than the Audio Research. The Audiopax was certainly kinder to recordings that were on the harsh side, the AR having a slightly forward quality in comparison: more revealing of faults in the source, but arguably more accurate.

These comparisons between amplifiers were made with the CAT SL-1 Ultimate preamp. Although the SL-1/VS110 combination worked well in general terms, there was a bit of preamp noise apparent (it disappeared when Mute was engaged), which made me wonder whether these components were ideally synergistic. My next step was to substitute the SP16L for the SL-1 Ultimate.

That done, the first thing I noticed was that the preamp-originated noise was now virtually gone: whatever noise that was present was low enough that I had to go within about a foot of the speaker to hear it, and muting the preamp output had almost no effect on it. I suspect that this difference between the two preamps was due to the fact that the SL-1 Ultimate has a gain of 26dB, whereas the SP16L's gain is only 11.5dB. When I combined the SL-1's high gain (attenuated, of course, by the volume control) with the VS110's slightly-higher-than-standard 28dB of gain, and listen through the high-sensitivity Avantgardes, it's no wonder that the preamp's residual noise became audible. The SP16L's lower gain brought the noise down to a more manageable level.

The other effect of replacing the SL-1 Ultimate with the SP16L was that the sound became a little softer and more forgiving, while continuing to evince the strong dynamics and extended bass that characterized the SL-1/VS110 combination. In absolute terms, the SL-1 was more transparent and more extended at the frequency extremes, but the SP16L/VS110 combination "clicked" in a way that was more enjoyable on a wider range of recordings, such as those close-miked Varèse Sarabande show-music CDs, which can sound pretty fierce in a highly analytical system.

The SP16L's remote control was convenient to use, the available volume steps sufficiently small to dial in the ideal level for each disc. In this respect, the SP16L was superior to the CAT SL-1 Ultimate, whose larger volume increments sometimes made me choose between a level that was just a bit too low and one that was just a bit too high—and, of course, the CAT lacks a remote control. However, while the SP16L's volume control provided, as claimed, excellent left/right tracking throughout its range, I was sometimes bothered the lack of ability to adjust channel balance. It's not that unusual for recordings to have a channel imbalance; with the SP16L you just have to put up with it.