Tube Power Amp Reviews

The only thing that excites me as much as finding an excitable new affordable component (which I define as below $1000, and the lower the better) is a new "trickle-down" design from a cutting-edge designer. Thankfully, such new "real-world" products are becoming more commonplace in the High End. The process begins when a talented high-end designer releases an expensive, cutting-edge product that is hailed by the audiophile press as a breakthrough, a new "reference." The designer then takes the most significant features of his cost-no-object design and reinterprets them in a more cost-effective format. Examples include the Conrad-Johnson Premier Eight amplifier, which begat the Premier Twelve; the MIT Terminator 2 and 3 cables, which feature similar network technology as found in MIT's priciest wares; and the Genesis 200 and 300 loudspeakers, which sport the same drivers and design philosophy as the big Genny 1.

My trickle-down juices really started flowing when I read the August 1994 issue of Stereophile, wherein Robert Harley raved about the Audio Research VT150, Audio Research's first attempt in many years at a cutting-edge, all-tube amplifier design. In that same issue Harley interviewed designer William Z. Johnson, who alluded to the impending release of the VT130, which Johnson described as "80 to 90 percent of the performance of the VT150...[at]...less than half the price..." [Wes Phillips reviewed the VT130SE in the November '96 issue of Stereophile, (Vol.19 No.11)—Ed.]

Bring on the tubes!!!
Ever since I heard the highly underrated M-100 monoblocks (paired with an Audio Research SP-10 preamplifier) driving a friend's Infinity RS-1bs 10 years ago (to date, one of the best Infinity-based systems I've ever heard), I've lusted for an all-tube ARC design I could afford. I was partially satisfied when, seven years ago, I bought my current reference, the Classic 60 (a tube/solid-state hybrid).

Unfortunately for me, the new VT-series amps didn't fit the bill as potential review fodder. The problem is, ARC threw me a curve with the VT150 and VT130 amps. Like the later versions of the hybrid Classic Series, they had one set of inputs: balanced. And Bob here, partly by preference and partly to maximize review interface flexibility, has a reference preamp (the Audible Illusions Modulus L1) equipped with only single-ended outputs. I've criticized ARC for years for manufacturing products that were inherently incompatible with most of the preamps on the market. (Though they do manufacture a not-inexpensive single-ended-to-balanced converter, adding a solid-state Band-Aid and an extra set of interconnects to the front end of a tube amplifier does not strike me as an acceptable compromise.)

At the 1996 Winter CES, after recovering from hearing the spectacular debut of Audio Research's new flagship Reference electronics driving a pair of Genesis 200 loudspeakers, I discussed the potential of future trickle-down designs with ARC's Mike Harvey (who has since departed the company for warmer climes than Minnesota). Harvey explained, "You know, the magic behind the Reference amplifier is not in the 600W. That was Johnson's choice, as this was intended as a cost-no-object design. It may be possible to capture much of the magic of this amp in a lower-powered design for under 10 grand."

"Of course, it will have balanced inputs, so I can't review it."

"Well, we still believe that balanced is best, and our engineers feel that providing both single-ended and balanced inputs would necessitate a sub-optimized design that may result in sonic compromise."

We then discussed my obtaining review samples of the VTM120 monoblock amplifier, ARC's first reasonably high-powered, affordable, all-tube design with single-ended inputs since the D125 from the mid-'80s.

A few months later, Harvey called me regarding the review samples. "You know, Bob, we're having second thoughts about sending you the VTM120. It's a relatively old design derived from the VT60, and, frankly, we've concluded from a marketing standpoint that monoblocks really only sell well in our higher-priced product line. We're not sure we're going to keep the VTM120 in the line [it's now available by special order only], but at HI-FI '96 we're introducing a new all-tube stereo amplifier called the VT100, which has the same power rating. You may like it better. Oh yeah—and at $4495, it's our first amplifier which features trickle-down technology from the Reference electronics."

"And the inputs?"

"The VT100 features both single-ended and balanced inputs."

"I thought your engineers thought that would result in a sub-optimized design."

"Well, they thought about the problem a little harder."

At this point Harvey could hear me breathing heavily and clawing at the phone.

Bring on the latest affordable amp design from ARC!!!
The VT100, a stereo amp rated at 100Wpc, uses four pairs of Svetlana 6550 output tubes and shares the more expensive VT130SE's ultralinear-configured output stage (see Wes Phillips's review), combined with partial cathode coupling designed for low output impedance and high current delivery. According to Audio Research's Chief Engineer Rich Larsen, these circuits run the screens a little hotter than does conventional pentode operation, but still offer higher efficiency with less signal loss than triode designs. The amp's fully differential, direct-coupled input and driver stages, derived from the Reference 1 preamp, feature 6922 dual triodes with FET constant-current sources designed to achieve a more accurate differential balance. As in the Reference 600 amp, the output tubes are mounted on vertical circuit boards, one for each channel, running along the left and right interior chassis walls. This results in a virtual dual-mono layout all the way back to the power transformer (with shared secondary winding), with independent, distributed energy storage and very short signal paths. The amp features the same heavy-duty, gorgeous speaker terminal posts (they're actually enjoyable to use) as the VT130SE.

Bring on the boring reviews!!!
After 13 years in the reviewing game, I've learned there are two ways to make a rave review really boring. The first is to use the "sonic checklist" technique, wherein the reviewer lists every important audiophile attribute, and goes on and on about how the component excelled in every way: "The amp was tonally neutral from the lowest bass to the highest highs, had incredible dynamics, both micro- and macro-, was neither dry nor overly liquid in texture, revealed gobs of detail, and produced a wide and deep soundstage with perfectly placed images on the stage. Unlike any amp I've heard before, this amp has so many strengths, and I can't seem to find any flaws." With the exception of one possible shortcoming I'll describe below, all of the above hold true for the VT100.

But that would make this a really boring review.

I could instead use the second sure-fire way to write a boring rave: the "I stayed up till all hours going through every record in my collection and, my God, it was as if I was hearing the recordings for the first time" method. I would go into gory detail about my favorite recordings, recapping why they sound so much better than ever before.

That also held true for my experience with the VT100. It would also make very boring reading.