Tube Power Amp Reviews

Designers frequently make minor changes in an electronic component's design throughout its market life cycle. As these changes tend to be evolutionary rather than revolutionary, manufacturers seldom make a big deal about a capacitor change here, a tube change or wiring reconfiguration there. This strategy is partly due to the company reluctance to get the market excited about subtle changes, and so not piss off the gal who just plunked down some heavy green for what she thought was the latest design.

Nevertheless, on informing the Audio Research Corporation that I wished to purchase the review-sample subject of my very favorable VT100 review (Stereophile, March 1997, Vol.20 No.3), the company insisted that I first ship the amplifier back to the factory for some minor updates, and to ensure that it was up to spec.

The most significant of these updates—the installation of InfiniCaps in several key parts of the circuit—made a minor improvement in the area of the amp's only significant weakness. In my original review, I had noticed a midbass thinness that I felt detracted from the VT100's overall neutral presentation. The InfiniCap mod fleshed out the midbass quite a bit, but the amp still lacked a degree of dynamic slam in that region that I heard with other amplifiers in my room, most notably the Sonic Frontiers Power 2.

Later, in the early part of this year, I received a call from ARC about an update to the VT100 that the company felt was significant enough to designate the new version as "Mk.II." I sent my sample back for the following updates:

• Replacement of the integral AC power cord with a thicker, higher-quality detachable cord. (In addition to the potential for sonic improvement, ARC felt this allowed the consumer to try some of the more esoteric AC replacement cords currently on the market.)

• An internal fan (to extend tube life).

• Proprietary, clear tube damping rings on the twin triode 6922 input-stage tubes (to lower the amplifier's noise floor).

• Doubling of the power-supply energy storage (to 540 joules).

That final upgrade has resulted in the VT100 now having the highest power-supply energy storage per watt in ARC's product line. By comparison, the highly touted VT200 (see Wes Phillips' review in the October 1998 issue) has 674 joules of energy storage. Principally as a result of this final, labor-intensive modification, the cost of the update to VT100 owners is $995, plus round-trip shipping to the factory ($595 if purchased after April 1, 1998). The retail price of the Mk.II version has also risen, by $500, to $4995.

ARC claims the Mk.II update results from the company's education derived from more recent designs, most notably the VT200. The company admitted that the ample space within the VT100 chassis is what permitted such a large increase in energy storage.

I tested the amplifier on both my old and new reference speakers: the Acarian Systems Alón V Mk.II and Circe, respectively. I was surprised at the significant improvement wrought by the Mk.II over the original amp. The Mk.II further extended the strengths of the original, while converting the amp's weak area into a new area of excellence, as follows:

• A richness in the lower midrange: All of the ARC preamp and amp designs I've heard over the last 10 years have shared the company's sonic signature; ie, a slight reticence in the lower midrange that at times gave the component a forward or slightly analytical quality. Although the original VT100 exhibited this characteristic less than any ARC product I'd heard in my own system (specifically, the SP11 Mk.II preamplifier and the D125 and Classic 60 power amplifiers), the ARC "sound" was still recognizable. Not so with the Mk.II. A supple sense of density and body (but not, in my view, a euphonic distortion) in this region enabled the amp to project vocals with a sense of body and dimensionality that imparted a greater sense of realism in the midrange.

• An uncanny sense of ease: The few times I was able to hear it at shows, one of the most impressive features I noted in ARC's Reference 600 amplifier was its sense of ease at reproducing complex high-level passages. When an amp gives the subjective impression that it's not working hard to impart a sense of realism, such effortlessness makes one forget that one is listening to an electronic simulation of a live musical event. This ease—which essentially means the amplifier does not change character as the program material becomes more difficult at high levels—is what separates a live performance from its electronic representation. This quality in the VT100 Mk.II enabled the amp to give a relaxed, unflustered presentation of all source material.

• Spectacular low-bass and midbass definition and dynamics: The old amp's greatest weakness was now history. The level of tightness, pitch definition, high-level slam, and control in the 25–100Hz region, whether on electronic dance music, hard rock, or full-throated orchestra, enabled this amp to hold its own even when compared with solid-state current dumpers.

• Dynamic contrasts: The subtle dynamic gradations and the continuousness of those gradations was what impressed me most about the original VT100. The Mk.II mod added one more p and f to the VT100's dynamic range, which was now the widest of any component I've heard in my listening room.

• Detail and ambience retrieval: Another strength of the original amp is further extended. With the Mk.II, I found myself following each instrument separately on well-recorded complex orchestral music. On rock music, I felt as if I was in the recording studio, analyzing the playback of the master tape. Furthermore, the ability to more easily hear the side and rear walls of the recording venue enhanced the soundstage presentation of orchestral and chamber works.

• Transient articulation: The VT100 Mk.II is the amplifier for percussion freaks. I found myself analyzing the performance of mallet percussionists, the air around the thwacks, the manner in which the timbre of percussion changed depending on how hard the instrument was hit and where on the instrument the mallet landed. On piano recordings, it was very easy to study the pianist's technique and articulation.

A single solo-electric-bass recording demonstrated all of these strengths: Dean Peer's Ucross (Jazz Planet/Classic JP 5002-1). All tracks on this dramatic recording reflected Peer's subtle articulation of transients, the sense of his fingers' skin on the strings, and the clear resonance of harmonics throughout the instrument's range. The ARC exhibited extension and speed without a hint of harshness or bite, and the resonant textures of the upper and middle bass fundamentals gave the impression of a bass guitarist performing live in the room. The seemingly unlimited and continuous micro- and macrodynamics were forceful yet intimate.

If you haven't bought into JVC's XRCD II process, you must hear the Modern Jazz Quartet's Concorde (JVC JVCXR-0203-2). I have never heard a more natural recording of vibes than on this recording when played through the VT100 Mk.II. The transient articulation of wood against metal, the perfect attack and speed without edge, and the flawless resonant decay of Milt Jackson's vibes were indistinguishable from those of a live performance.

This here HDCD freak heard his favorite HDCD recording, John Rutter's Requiem (Reference Recordings RR-57CD) as he never had before with the Mk.II. The ambience and body on the vocals, the manner in which the vocal choir was perfectly layered along the center and rear of the stage, and the earthshaking but intimate organ pedals—as well as an enhanced sense of room sound—gave the recording an eerie and realistic quality that made me forget I was listening to digital.

I should point out that the upgrade of my reference speakers to the Alón Circes made a particularly good match for the VT100 Mk.II. Although the Circe is more ruthlessly revealing of electronics' shortcomings than the Alón V Mk.II, the ARC amp revealed no noticeable flaws with this speaker. Part of the synergy between these components is due to the fact that the Circe shares the Mk.II's six major strengths; it was in just these areas that, in my room, the Circe outperformed its less expensive sibling, the Alón.

If you haven't guessed by reading between the lines, on both sets of speakers the VT100 Mk.II behaved like an amplifier that was much more powerful than its nominal 100W rating (admittedly, neither Alón speaker is a particularly difficult load).

The VT100 Mk.II exhibited no noticeable flaws in my system with either set of speakers, and there wasn't a single strength of the amplifier that I felt could be improved on. I'm at a loss to fathom how ARC is going to sell any VT200s once customers hear what this little 100W baby can do.—Robert J. Reina