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VTL MB-450 Series III Signature Power Amplifier

VTL MB-450 Series III

The VTL MB-450 series began life in the late 1980s as the Deluxe 300, a pair of which I once owned. Over the years the basic design has been improved and modified, in the forms of the MB-450 (1996) and the MB-450 Series II (which I reviewed in January 2008). The tube complement remains the same: eight 6550s in the push-pull output stage, a 12AT7 input tube, and a 12BH7 driver. Into a 5 ohm load, the MB-450 III is claimed to produce 425W in tetrode mode or 225W in triode, from 20Hz to 20kHz.
The Series II added VTL's Smart Tube technology, also found in the company's flagship Siegfried line. This optimizes tube performance through the use of logic-controlled auto-biasing, which continually monitors each tube, and adjusts its bias on power-up as well as when the system is idling. It also includes a diagnostic system: If a tube malfunctions, the amp indicates that with an adjacent LED and shuts down if the tube draws excessive current.

VTL's goal for the Series III Signature revision was, first, to improve the MB-450's ability to better drive a wider range of loudspeakers. These changes include a redesigned, fully balanced differential input stage driving a differential phase splitter, and a lower-impedance push-pull output stage terminating in an output transformer that is now fully balanced, and claimed to be "dramatically improved." The Series III also has a shorter, faster, fully balanced negative-feedback loop. VTL claims that this circuit completely eliminates ringing and maintains phase integrity without using capacitor compensation.

Precision-regulated power supplies for the output tubes' bias supply and screen voltage maintain the tubes' operating-point consistency, even when the AC supply fluctuates. VTL claims that this produces tonal stability and "sonic integrity" in the reproduction of complex, dynamic signals.

A front-panel button allows the MB-450 to be switched between tetrode and triode operation for the output tubes. Although there is a Mute button, switching the operating mode can be performed without having to mute the amplifier. The four settings of the Damping Factor toggle switches behind the glass window on the front panel vary the MB-450's output impedance by changing the amount of negative feedback in the circuit. The Low setting minimizes damping and to produce the "most natural sound," per VTL, while Med (Medium) has a minor impact on the overall sound but produces somewhat better speaker control. The Hi setting further improves speaker control, but has a greater impact on the sound; and Max applies the iron fist of maximum feedback, but with a noticeable negative sonic impact, according to VTL.

VTL claims that the addition of pricey premium Mundorf silver-oil capacitors produces a sweeter, more extended top end, a more relaxed-sounding midband, and superior midbass control. An MB-450 Series II can be upgraded to Series III status.

Description

The Series III looks very similar to the Series II, with one significant exception. Now, to access the tubes, instead of removing the entire cover, which was unwieldy, VTL has cut from it a pair of small L-shaped sections directly above the output tube sockets, making them far easier to remove and replace.

Otherwise, with its gracefully curved front panel of matte brushed aluminum and tinted glass, the MB-450 remains a substantial piece of kit built to an extremely high standard—which is what you should expect to get when you plunk down $18,000 for a pair of them. The beefy speaker terminals can take a hard torqueing, and everything else on the rear panel, as well as what's inside, is industrial grade.

Setup

While VTL's instructions suggest that unpacking each MB-450 Series III Signature is a two-man job, I managed it myself (thanks to the gym). No doubt your dealer will do this for you, but if not, be careful. Not only does each amp weigh 93 lbs, but because its transformers concentrate most of its mass in the rear, lifting and carry can be awkward and tricky.

The manual is usefully detailed, helpful, and informative, but sometimes makes the simple seem complicated: "For the MB-450 amplifier, there should be a total of 8 sockets for the output tubes. . . ." Should be? Is someone at VTL worried that a tech might have omitted a few sockets?

The output-tube sockets are numbered 1 through 8, but all of the 6550C tubes, which were separately shipped in another box, were labeled "#2," while two spares packed with the amps were labeled "#7." This caused some confusion, particularly as the instructions tell you to "Insert the output tubes into each of the output tube sockets from tube #1 to #4 on the left side of the cover and 5 to 8 on the right side of the cover."

VTL's CEO, Luke Manley, told me that the manual was written by his wife, Bea Lam, who feared that a more direct tone would sound bossy. I say go for it, girl! Don't be afraid to write: "Remove the covers and insert output tubes into the eight sockets." We'll know not to insert more than one in each socket. Of course, the auto-biasing circuit makes matching the tubes irrelevant, a point Manley reiterated when he visited my listening room to make sure everything was going well. Why even mention the socket numbers?
Manley had brought along four spare B+ fuses, and extra input and driver tubes. Better to be prepared in the event of a tube failure, in which case the MB-450's microprocessor-controlled design helps ensure that, at worst, you'll be replacing a tube and a fuse instead of shipping the amp back to the factory for more extensive and expensive repairs.

VTL MB-450 Series III back

The MB-450 Series III Signatures were in my system for three months, during which we experienced a severe windstorm; the power came and went, and there were many brownouts. The amps proved completely reliable; they ignored the brownouts, while each interruption of power caused them to revert to Standby mode.

Pushing the Power button turns the amp on. Hitting Mute both mutes the input and draws down tube current to a trickle. VTL suggests leaving the amps in Mute mode overnight, if you plan on listening the next day. Then, on startup, they'll be warmed up and ready to go. For extended non-listening periods, hit the Power button to completely shut down the amp. From a cold power-up, don't expect the MB-450 III to sound its best for an hour or so.

Sound

Luke Manley switched among the four settings of the Damping Factor control so I could hear the results of each from my listening position. Low sounded too sloppy for my tastes and my Wilson Audio MAXX 3 speakers, but Med tightened things up nicely. The other positions sucked the air out of the room, so Med it was. Your preference may vary with your taste and speakers. It's nice to have the flexibility.

Going from a megawatt solid-state amp to a powerful, competently designed tube amp no longer produces a seismic sonic shift—at least in tetrode mode. In fact, there was somewhat of an unexpected role reversal. Forget about warm, soft, rolled off—the MB-450 Series III's top-end extended smoothly out to the highest reaches. By comparison, my big Musical Fidelity Titan reference sounded somewhat less exuberant in the high treble, if equally refined.

Overall, in tetrode mode, the MB-450 Series III ran a fast, tight, lean, rhythmically nimble ship—the opposite of what "tube sound" is supposed to denote. Running the amplifier in triode mode did indeed produce the soft, tubey sound some like, but I don't. I ran the VTL in tetrode throughout the review period.

Do you like gobs of air and superior spatial projection? Do you like it when everything floats effortlessly in space, freed from the confines of the speakers? The MB-450 IIIs did that with ease. Their top end was as generous and expansive as you'd expect from the best solid-state amps, with unusually fast, precise attacks, but without any of the grain, glare, and etch that often accompany those attacks in the solid-state realm. The MB-450s didn't miss a molecule of air or a single cymbal rivet. VTL's specs show flat response to 20kHz. I believe it.

The clarity, transparency, and physical refinement of the VTL's reproduction of high-frequency transient information produced realistically sharp edges—the kind I don't normally associate with "tube sound," or with all that much solid-state sound, either. The MB-450's sustain was what I do expect from tubes: extended and expansive, with overall decay structures that were graceful and generous, even if the fade was more to dark gray than to the black you get from the best solid-state amps. I'd noticed this quality of the MB-450 in VTL's room at the 2010 Consumer Electronics Show, and now I heard it in my listening room.

VTL MB-450 Series III top

Classic Records' reissue on nine single-sided, 200gm, 45rpm LPs of The Royal Ballet: Gala Performances, with Ernest Ansermet conducting the Royal Opera House Orchestra (RCA Living Stereo/Classic LDS-6065), puts the listener in the airy space of Kingsway Hall, the orchestra arrayed on an ultrawide and ultra deep stage. This recording lets me hear into the stage's deepest recesses, and layers ranks of instruments from front to back with great precision, and the MB-450s reproduced all that it offers.

The MB-450 III's crystalline finesse in the treble never ceased to excite. Cymbals, bells, and celeste were reproduced with effervescent precision and sophistication: tiny when appropriate, but always precise. It's almost impossible to go ice-crystal precise on top and not pay a price in terms in the richness of string tones lower in the audioband, but the MB-450s managed a fine, realistic sheen on massed and solo strings alike, producing an ideal balance of bow on string and the resulting woody resonance.

Like the Series IIs, the Series IIIs produced "enhanced holographics" compared to my current reference amp, the Musical Fidelity Titan, which couldn't match the 450's airy expansiveness. While the VTLs' reproduction of space was more generous and their soundstage wider, deeper, and more vivid, it was never bloated, nor were images on that stage diffuse or lacking in weight or body. Still, the solid-state Titan was superior in the latter regard, producing greater body and weight and, especially, image solidity. Which you'd prefer would be a matter of taste.

Like the MB-450 II's, the III's low-frequency extension was seemingly complete—deep, solid, and especially well controlled—with the result that the sound of the III was rhythmically nimble and texturally revealing. It gave ground to the MF Titan in terms of bass weight and, especially, bass dynamics, where it seemed lighter and somewhat more polite, and less able to produce visceral, stomach-slamming drive. Of course, one listener's "drive" and "weight" are another's "sludge."

Switching back to the Titan produced more satisfying bass weight and drive, but nothing seemed to be missing from the MB-450 III's reproduction of a recent AAA reissue of the Jimi Hendrix Experience's Axis: Bold As Love, mastered by George Marino for 180gm vinyl (Legacy Records). In fact, the shimmer of Mitch Mitchell's cymbals seemed to extend more cleanly and with greater clarity further into the stratosphere than I'd ever heard it. The decay of that shimmer was notably more clean and graceful than the Titan's somewhat darker rendering. However, the big solid-state amp produced more visceral weight with electric bass and kick-drum that more effectively propelled the music forward.
When the Musical Fidelity was in the system, I missed the VTLs' crystalline cymbal shimmer and air. When the MB-450s were in the system, I missed the Titan's stomach-slamming low-frequency weight. But if there's a single amp that does both as well as each of these two doing what it does best, I've yet to hear it.

Missing from the sound of the MB-450 III was the slightly "splashy" quality to transients that gave cymbals and sibilants that "more prominent role than I was used to hearing from familiar recordings" that I noted in my review of the MB-450 II. Instead, as already noted here, sibilants were consistently rendered cleanly and precisely, as were cymbals and other instruments that produce high-frequency transients. In fact, the MB-450 III set a new standard in that regard for my listening room.

The MB-450 III's reproduction of female voices was mesmerizing. Ella Fitzgerald's Twelve Nights in Hollywood (4 CDs, Verve B001292002), recorded live at the Crescendo in 1961, hadn't yet been released when I reviewed the Series II, but she always sounded full-bodied and clean through the big Titan, as did Aretha Franklin when I played her I Never Loved a Man the Way I Love You (gold CD, Atlantic/Rhino/Mobile Fidelity Sound Lab 574).

The MB-450 Series IIIs produced a different perspective on Fitzgerald's voice: one more spotlit, with less body and more throat, more room context and somewhat less intimacy. Through the Titan she sounded richer, but through the VTLs she sounded smaller, more precisely drawn, and more of her singing technique was revealed. I could visualize more of what her mouth was doing, but less of the picture's completeness. Which was better, or more "correct"? Who knows? What seat in the house was more "correct?" What picture was the engineer trying to reproduce? Who knows?

The Aretha Franklin album produced a similar shift of perspective: Her voice was more generously drawn through the Titan, and was heavier in her lower registers. The MB-450 IIIs' picture was airier and more tightly focused, with greater emphasis on the vocal cords, less on the chest sound.

The MB-450 Series III was voiced with VTL's tubed preamplifier, and I suspect a tube preamp would better match its personality than the solid-state darTZeel NHB-18NS I use, which so well complements the warmer-sounding, solid-state Titan.

Power to Spare

I found that 425W into 5 ohms was more than enough power to drive and effectively grip each of my Wilson MAXX 3s, which are more sensitive than the MAXX 2s. The MB-450 IIIs never ran out of gas, even at the climaxes of orchestral crescendos played at realistic SPLs; overall, their dynamic capabilities were complete at both ends of the scale. Considering the cost, the complexity, and the heat, the MB-450 struck a pleasing balance of power, finesse, and practicality.

That the Musical Fidelity Titan swamped the MB-450 IIIs in bass and midbass dynamic thrust was immediately apparent when I switched back to it—but some of the attractive qualities produced by the VTLs were now gone. My immediate response on switching from the MF to the VTLs was "Where's the weight?" In the opposite direction, it was "Where's the air and shimmer—and how can I live with that thickness?"

Conclusions

The VTL MB-450 Series III Signature is a significant evolutionary advance from the MB-450 Series II Signature. It's a much better sounding amplifier—a clearly smoother-sounding performer that's less likely to show its sonic seams, as the II occasionally did. Their unquestioned transparency and wide bandwidth made them difficult to "hear"—about as high a compliment as can be paid any audio component.

Through the MB-450 IIIs, the top and the bottom ends of the audioband sounded and felt complete. The lower octaves, in particular, were tightly drawn and well extended. I never wished for more grip or extension. In some ways, particularly on top, the MB-450 sounded more like a spectacular solid-state amp. Only its superior flow—its long sustain and clean decay—gave away that it it's a tubed design. It sure wasn't hissy or noisy, and it never sounded like a pleasant "tone control," as some ripe-sounding tube amps are accused of doing. In fact, the MB-450's sound was more on the lean side, with a somewhat less-than-generous lower midrange and upper midbass combined with fast, airy, sparkling upper octaves and tight, nimble lower ones.

The MB-450 Series III Signature combined a great solid-state amp's upper-frequency speed and clarity and bottom-end extension and grip with a great tube amp's musical flow, though there remained still more true weight (not bloat) to be had on the bottom that, in my experience, can be produced only by a big solid-state amp.

I know I could live happily with either the Musical Fidelity Titan or the MB-450 Series III Signatures because, for a few months, I lived happily with both, switching between them to enjoy and appreciate what each brought to the sound of my system and recordings. I appreciated the Titan's added weight and punch on bottom and its rich yet detailed upper octaves. When the MB-450 IIIs were in circuit, the air, space, and speed made listening engaging and enjoyable, and though bottom-end dynamics were somewhat less pronounced, the VTLs' speed and extension more than compensated, to produce fully satisfying bottom-octave performance and exceptionally fine rhythm'n'pace with even the hardest-rocking records.

Like the MB-450 Series II Signature, VTL's MB-450 Series III Signature is easy to recommend.

Specifications

Description: Tubed monoblock power amplifier with switch selectable Damping Factor (four levels available). Tube complement: one 12AT7, one 12BH7, eight 6550C. Inputs: 1 pair unbalanced (RCA), 1 pair balanced (XLR). Outputs: 1 pair binding posts. Rated power output at <2.5% distortion into 5 ohms: 425W (24.25dBW), tetrode; 225W (21.5dBW) triode. Frequency range: 20Hz–20kHz at 450W (tetrode) or 200W (triode). Optimal load range: 4–8 ohms. Input impedance: 42k ohms. Input sensitivity: 775mV–2.0V for full output, depending on DF setting. Power consumption: 30W at idle, 1000W at full power.
Dimensions: Each: 18.5" (470mm) W by 9" (230mm) H by 18" (460mm) D. Weight: 93 lbs (42kg) net, 110 lbs (50kg) shipping.
Serial Numbers Of Units Reviewed: 10418588/9.
Price: $18,000/pair. Approximate number of dealers: 40. Warranty: 5 years electronics, transferable.
Manufacturer: VTL Amplifiers Inc., 4774 Murrieta Street, Suite 10, Chino, CA 91710. Web: www.vtl.com.

Article written by Michael Fremer

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