Tube Power Amp Reviews

Since Chip Stern's update on VTL's second-generation MB-450 Signature back in October 2002, the amplifier has undergone further changes and improvements. It now features a completely redesigned input stage that incorporates advances made during the development of VTL's mighty Siegfried monoblocks. The '450 now has a true balanced input stage, the asserted benefit being superior common-mode noise rejection without the use of an input coupling transformer. Despite these improvements, the MB-450's price remains unchanged: $10,000/pair.

The new differential input stage consists of a high-gain 12AT7 tube to provide broad voltage swings, with B+ regulation and a constant-current source to maintain equal drive between the two phases even as the tube ages. Sez VTL main man Luke Manley, "This stage offers 60dB of common-mode rejection to external noise and other interference, and will accept also a single-ended signal on either phase, and will develop a signal on the opposite phase to drive the next stage."

The input stage is capacitor-coupled to a 6350 tube, this comprising a differential phase-splitter driver stage. The two halves of the tube form a long-tailed pair with a constant-current source, providing high voltage swing with equal drive to both phases of the push-pull output stage via series capacitors. The output stage remains unchanged—why mess with a good thing? Each amp still has eight 6550C power tetrodes and produces a very robust 450W into 5 ohms. Switch over to triode mode and you still get approximately 200W. As Rolls-Royce used to put it, power is "sufficient."

Evaluative listening was done principally with the Halcro dm10 full-function preamplifier and VTL's own TL-7.5 Reference line stage, fed by an Aesthetix Io Signature phono preamp. BAT's VK-51 SE line stage also put in an appearance. Speakers were Focal-JMlab Nova Utopia Be's. Classé's superb Omega SACD/CD player decoded the digits, and vinyl was handled by my regular analog rig of SOTA Cosmos Series III turntable, Graham 2.2 tonearm, and Dynavector XV-1S cartridge. Signal wiring included Nordost Valhalla, Siltech Classic, and Acoustic Zen Silver Reference. AC was provided via Shunyata Anaconda, Anaconda VX, and Siltech SPX-30 cords, with Shunyata's Hydra 8 conditioning and distributing the power. The MB-450s sat, as amps usually do chez Bolin, on Grand Prix Audio Monaco stands.

I've said it before: There's something really special about a great, massively powerful tube amplifier. The sensation of seemingly unlimited reserve power at any sane listening level let me relax totally into the music—the VTLs were not going to run out of gas no matter how hard I drove them. Dynamics were consistently first-class. The Minnesota Orchestra's colossal dynamic swings in Rachmaninoff's Symphonic Dances (CD, Reference RR-96CD) flustered them not a bit. Even during the most intense passages, the '450s never sounded even mildly stressed. Forceful music was always re-created with exceptional ease and refinement.

The MB-450's sonic character was big and luxurious, but not overly "tubey" in the old-school sense of the term. There was the natural musical warmth that tubes do so well, but nothing in the amp's character could ever be called "loose" or "unfocused." Images were always cleanly delineated, but in a way that called to mind the traits of live music far more than it did those of hi-fi. Inner orchestral voices—such as those in the performance of Schumann's Piano Concerto by pianist Byron Janis, Stanislaw Skrowaczewski, and the Minneapolis Symphony (LP, Mercury SR90383)—were revealed in precise place and proportion. Janis' piano rang clean and true, every note differentiated cleanly and distinctly. With Emmylou Harris' "I Ain't Livin' Long Like This," from Spyboy (CD, Eminent EM 25001-2), Buddy Miller's smokin' guitar solo was superbly articulated and left me shaking my head in awe at his masterful playing. The '450 was suave and satiny at the top of the spectrum, with good extension, and detail retrieval that was definitely better than average.

The VTL's midrange showed excellent transparency and detail. Timbre was what one might reasonably expect from an outstanding tube amp; the MB-450 was harmonically generous and true to both voices and instruments. Bass control can be a concern when tube amps are paired with such large drivers as the ported 13" units in the Nova Utopia Be's. The VTLs put those high-tech, low-mass woofers in a bear hug—definition was excellent, and extension left no room for complaint. Daryl Johnson's rumbling bass on Wrecking Ball on Harris' "Where Will I Be?" set things abuzz in my room. That potent bass was cleanly articulated and showed convincing bloom.

Soundstaging lived fully up to expectations: capacious, cleanly delineated, and enveloping. With the VTLs, I always felt myself a part of the environment created by the recording, not a disconnected observer of an event happening elsewhere. Backgrounds were as quiet as the best I've heard from tubes, namely the Lamm ML1.1, and that is very quiet indeed.

Switching over to triode mode brought a degree of voluptuous roundness to the VTL's presentation and moved the musicians an inch or two closer to me. There was also a jot or two of extra sparkle in the lower treble—perhaps a touch of romanticizing—and top-treble detail retrieval, while still very good, was not quite as evenly illuminated as in pentode mode. Bass became a little loosey-goosey at times in triode as well, but not so much that it could ever be described as "mushy" or "ill-defined."

While triode mode was excellent with orchestral music, its particular strengths perfectly suited smaller-scale music. Simon Nicol's remarkable vocal on "The Deserter," from Fairport Convention's XXXV (UK CD, Woodworm WRCD038), fuses moral passion and muted anger in quite an astounding way, and Rickie Lee Jones' take on "Walk Away René," from Girl At Her Volcano (LP, Warner Bros. 23805-1B), was even more heartbreaking than the Left Banke's immortal original. Triodes do, it seems, bring an extra level of emotional directness.

Ultimately, triode giveth extra warmth and touchability and taketh away some ultimate bass definition and dynamic slam, as well as the last few squillionths of resolution that pentodes provide—a fair trade. That both are available at the flip of a switch (after being sure to turn the MB-450 off) gives the MB-450 owner a mighty appealing set of choices.

The VTL MB-450 Signature offers a boatload of performance and power in a thoroughly engineered, straightforward, solidly built package. It will drive any speaker I can think of in pentode mode, and will drive nearly any speaker in triode mode. Its sound is open, inviting, and truthful in revealing both the artifacts of recordings and the essences of music. It is one very fine amplifier that should be heard by anyone shopping at this end of the market.—Paul Bolin