VTL MB300 & MB450 Signature monoblock amplifiers Michael Fremer 1999 part 2
While setting the bias is less convenient without the built-in meter, it's still relatively easy (once you remove the cage) using an inexpensive RadioShack digital meter, a plastic-shafted or insulated flat-blade screwdriver, and the well-written instructions. During the year or so I had the 450s in and out of my system, the bias settings on the 16 tubes hardly drifted from the specified 27mA quiescent current draw.
The MB450 is compact but extremely heavy, most of its weight awkwardly in the rear of the chassis, where the power and output transformers are located. Moving and placing the amp is tricky: while you can carry it around using the front-mounted handles, setting it down without resting its weight on the rear panel is almost impossible—another reason the binding posts and triode/tetrode switch have been angled up and out of the way on the new rear panel—a really good idea.
The heart of any conventional vacuum-tube amplifier is its output transformer, and here is where VTL has made the most significant change. The new Signature transformer is said to be a far more sophisticated and efficient design that results in "better current transfer from the tubes," according to Manley. So much better that, using the same eight output tubes, VTL claims a one-third gain in power output: from 300 to 450W at 8 ohms.
The new transformer has, according to VTL, ultrawide bandwidth and very low loss, due to multiple tight layering and coupling of the primary and secondary windings—which, the company claims, also results in very clean squarewave response. (For more information on VTL's Signature transformer, including an upgrade program for owners of older VTL amplifiers, check out the VTL website.)
One immediate difference between the pre-Signature MB300s I owned and the MB450s was clearly audible before I listened to a note of music: the new amps were much quieter, with no discernible mechanical transformer buzz. The 300s thrummed.
VTL has managed to substantially improve and refine the sound of this amplifier without losing any of its previous greatness; the MB450 retains the MB300's rich, robust sound.
The big VTL amplifiers have always excelled at creating a large soundstage and an enveloping sense of space, and the 450s did not disappoint in that regard. On Chesky's great Olatunji CD Love Drum Talk (WO160; also on 24-bit/96kHz DVD, CHDVD180), the naturally reverberant church venue was portrayed with a large, dramatically enveloping sense of height, depth, and width.
Tony Bennett's Live at Carnegie Hall, Vol.1 (Columbia CS 8705), from 1962, highlighted the 450s' ability to map out a big, airy space while offering fine focus on the main event. It's funny to hear Bennett say, "Here's a brand-new popular song," then launch into "I Left My Heart in San Francisco"! The engineers did a great job of presenting an honest perspective, the drum kit appearing way back on the stage, not spotlighted by close miking. If you've heard jazz in Carnegie Hall from the middle of the room, this recording through the 450s will put you there.
Bennett appears center stage as a focused, three-dimensional apparition, yet with a natural airy boundary between his image and the supporting ether. It's damn convincing—even without a center channel and surrounds. How do they do it? When Bennett hits the climactic high notes on the final chorus, you can feel the air in the hall pressurize and set off a typically warm, controlled Carnegie Hall reverberant event. A perfect recording to show off what the 450s do best.
While the old 300 lost ground at the frequency extremes, the 450 provided a far more solid and well-defined bottom end, with less bloomy midbass and plenty of wallop at the very bottom. While the 450 isn't the punchiest amp I've heard in the bass, its sheer weight and solidity more than compensated. On top, compared to the original 300 (as I remember it), the 450 had a sharper, more immediate attack, with crisper, better defined transients.
The MB450 was just on the right side of thick and rich in tetrode mode. Switching to triode resulted in an increased purity with more than enough power to drive the Audio Physic Virgos, but the overall sound was too ripe for my tastes. But that could be the speakers; the Virgos are on the warm side to begin with.
While the MB450 is a faster, more neutral edition of the classic VTL amp, it still sounds more slow, dark, and thick than some other tube amps, including VTL's own MB 175, which I reviewed in June 1997 (Stereophile, Vol.20 No.6). That amp, designed for small-woofered speakers, sounded fast and nimble, with a snappier sense of rhythm and pace, punchier bass, and a more open, extended top end.
If you liked the sound of VTL's original big amps, you'll appreciate this latest incarnation even more (footnote 1). That wasn't the case when the company switched a few years back to KT90 output tubes. Many listeners found the sound sharp and somewhat glary on top, at least until the tubes had undergone extensive burn-in. While the KT90s made the amps sound faster, midband richness and weight were seriously diminished for many listeners.
VTL's amplifiers now feature 6550 output tubes. If you need lots of clean tube power to drive large speakers, and you want a dependable pair of amps that deliver a big, rich, three-dimensional sound at a (relative) bargain price, the VTL MB450s should be on your radar screen.—Michael Fremer
Footnote 1: It's easy to understand why the big Martin-Logan Statements, with their fast, clean, open, transparent midrange and pristine highs, were such a perfect match for the multiple 1250W VTL Wotans at HI-FI '98—especially given the giant room—and why the combination proved so popular with the public. No matter how much we'd like it not to be, it's a mix'n'match world, and that combo worked to perfection.—Michael Fremer