VTL MB-450 Signature - Series II

Review

by James Leahy

Beautiful designed and outstanding performance -  VTL MB-450 Signature Series II Monoblocks!

As of Dec 2009, these are my new Reference amplifiers . Why? For a number of reasons that I will explain. For an introduction I will let VTL explain in their own words the design philosophy behind their latest MB-450 design. No point doing the same work twice, then I will give you my thoughts in more detail.

"The Series II now incorporates VTL's advanced Auto Bias and Fault Sensing technology-features formerly available only with our flagship Reference products. A revised power supply and improved electronics give the MB-450's an ultra-fast transient response and a dynamic range.

The MB-450 Signature Monoblock Amplifier (including its predecessors) has been a core model in the VTL line for almost 20 years. With the release of the Deluxe 300 monoblocks in the late 80's, VTL successfully introduced a high power amplifier that could drive a wide range of speakers and yield outstanding performance for a reasonable price. The model evolved incrementally over the years, including a name change to the MB-450 Signature Monoblocks in 1996.

The MB-450 Series II Signature Monoblocks debuted in 2007 and incorporate many of the recent technological advances first introduced in the flagship 800W Siegfried Reference monoblocks in 2004. The essential elements of Siegfried's "smart-tube" technology are now standard with the MB-450 Series II. This system encompasses logic-controlled automatic biasing--which continually checks each tube for optimal performance--and an array of fault-sensing diagnostics that alert users to the operating status of each tube.

The "smart tube" technology puts an end to the guesswork formerly inherent in large tube amplifiers, making the new MB-450s easier to use and maintain. Other technology that has trickled down from the Siegfried amplifier includes a precision-regulated power supply and upgraded circuitry components. As a result, the MB-450 has attained new thresholds of sonic performance, with greatly improved bass tightness and dynamics. Compared to former versions of the MB-450, the Series II offers an unrestrained sense of openness, tighter and more controlled bass, and an ease and musical neutrality that give you the most satisfying listening experience.

An all-tube amplifier, the MB-450 Series II is the culmination of VTL's most advanced thinking in performance engineering. A proprietary regulated power supply, high-grade parts, and an automatic tube bias system ensure ultra high fidelity audio reproduction, while tube fault diagnostics and user feedback offer the ultimate in usability and convenience.

The audio amplifier is comprised of a fully balanced input stage and a long-tailed differential phase splitter, coupled with a push-pull output stage. Within the latter section is a logic-controlled auto-bias system that continually checks and adjusts the output tubes to ensure they are operating at optimal condition for proper balance across the output transformer.

The power supply section is similarly advanced: All critical voltages are precision regulated for consistent and predictable performance under a wide variety of conditions. Large energy storage reservoirs mean that the amplifier is capable of delivering huge peak current swings into demanding loads for powerful musical performance.

Optimized operating voltages and timed current inrush limiting dramatically extend tube life, with low idle current draw on all stages. An ever-warm position further lowers idle current while keeping all voltages present so the circuit remains warm when not in use.

The amplifier can run in one of two operating modes: Tetrode or Triode. The user can change mode either in standby or in power-on mode. Users often prefer one mode to another, depending on the type of music. For example, Tetrode may offer a wider sound stage and greater dynamics for complex and demanding symphonic music, while triode may work better for small ensembles or solo instruments."

Form Factor

How big is too big? I estimate the mass closer to a hefty 50kg each rather then what VTL lists. They are the largest amplifiers I can comfortable move by myself and relocate. This was a must in my buying requirements and amplifiers that I cannot move without help can be more restrictive. These must be shipped on pallets, Ground Shipping is way out of the question. A special note to users of such equipment, VTL recommends and so do I that you do not do as I do but always seek help when unpacking and/or moving these amplifiers. Please do not attempt to move them yourself.

Style / Design

If I am going to have to look at them everyday all day I want something I want to look at. I'm a very visual kind of guy as many of you might have alluded to already. If I'm not attracted to something I just can't get turned on no matter how much I try to talk myself into it. This is not an issue with the MB-450 Signature Series II Monoblocks, from every angle they look the business and I know I will not want to replace them any time soon. VTL have transformed their entire range to a very modern, dapper and leading-edge design. The curvaceous 0.75" thick front panel milled from a solid one piece aluminium billet with smoked glass insert projects a sophisticated and timeless design. The protective outer cover lends itself to a very functional and well ventilated design. As if this wasn't good enough there are removable sub-panels that allow quick and easy access to the vacuum tube area. This is a Godsend and negates the need to remove the entire outer top and side cover.

Intelligence

In my youth when I was under the influence I have been known to put beauty before brains now and then to get the job done when times were tough but it is all a learning experience. VTL have come down the same path but in a different way. VTL's Smart-Tube Technology really gives these amplifiers a tremendous edge with auto bias control. When you have any large vacuum tube amplifier with so many output tubes this new technology certainly makes them easier to live with, maintain and at the same time provides a superior level of performance from always being optimally adjusted every time you switch your system on.

High Power

Driving my beloved B&W Nautilus 800 Loudspeakers I wanted a pair of vacuum tube Monoblocks with massive reserves of good clean unrestricted power. I like to over do things by quite a considerable margin and having an excess of quality vacuum tube power behind every note is totally fine with me. When I buy something I want to buy it once and once only. Not feel the need to up-grade a year or less later to something else that I knew I should have bought the first time around but I didn't because I want too much of a cheapskate. With over Four Hundred of VTL's finest watts per Monoblock I knew they would do quite nicely and would be more than capable of driving any loudspeaker I would ever want to power. Using 8 x 6550C output tubes per channel this makes for some serious firepower for the power hungry like me.

Having listened to VTL's own massive MB-750 Reference Series Monoblocks I was concerned I would not be as impressed with the MB-450 Series II in the slam and attack department. This concern of mine and speculation of lesser performance proved to be unfounded and false. After talking to Bea Manley she assured me I would be even more impressed with this new model and not to be concerned with the specification sheet and she was correct.

The new MB-450 Series II's are a truly stunning amplifiers. They have greater speed and attack than the older style amplifiers, due to the auto biasing and real time fine tuning of tube operating parameters. They also produce greater resolution - and in micro dynamics they have the edge without sacrificing any control or slam power. You will only understand what I am trying to explain when you have heard them.
 

Silent Operation / Cooling

Working in a small office and when listening to quiet musical pieces even the smallest and quietest of cooling fans can cause distraction. The heat dispersion issue has been very well thought out in this design with passive heat control management VTL have employed. They require at least 12 inches clearance around the top and sides of the amplifier's chassis. Ideally you should have them placed in an open location with plenty of air circulation and when you look this good if you've got it flaunt it. The MB-450 Signature Series II monoblocks are such a visual delight and showpiece for what is possible today in State-Of-The-Art vacuum tube engineering I have them sitting in pride of place on my office desk. They do run hot as you would expect as when generating this much power the by product is of course heat.

Protection / Safety

VTL is very serious about making their vacuum tube products easy to use and accessible to more music lovers then ever before. In the past some users have been apprehensive about getting into the world of vacuum tubes because of the perceived added maintenance and/or reliability issues.

It is this single factor that I believe sparked Luke Manley's original vision and dedication which led the company to build more user friendly products with the MB-185, MB-450 and Siegfried Monoblocks being the ultimate in his designs and all using 'Smart-Tube' technology. This technology first appeared in their Reference amplifiers the Siegfried's and then only 3 years later the benefits of this development has been provided in the Signature Series.  Good things surely do come to those who wait in the lovely world of VTL.

Even VTL's their entry level models such as the IT/ST-85, MB-125 and ST-150 that I have had much experience with are built to such a high standard that reliability issues are not a factor. The amplifier design is very robust and well has good passive protection by fuses an all circuits that major system failure which requires a workshop repair is unheard of to me.

When you get up into the hundreds of watts and start using more than four output tubes per channel in order to develop these huge power levels; the need for sufficient protection is more and more essential. As the number of output tubes increases the current level generated by the transformer must also increase by the same percentage to drive them. This raises the potential for sever damage to the circuit if a vacuum tube fails exponentially. Thus it also stands to reason the more output tubes you have the greater likelihood of getting a failure at some point in the day in day out operation. So you have two factors that are working against us in terms of reliability at these power levels. Extremely high current and the total number of output tubes.

I typically on average use my personal VTL MB-450 Series II Monoblocks around 12 hrs/day, everyday. This equates to over 4,000 hrs/yr of tube drenched power. This could be classed as 'Extreme Use' and there are not a lot of amplifiers in this power range that can take this punishment without serious reliability issues. When spending this sum of cash on amplifiers you want total piece-of-mind assurance that they can be used all day every day at full output if required; without fail.

I know of no other gigantically powered, stone cold reliable, power amplifiers designed for 24/7 'Mission Critical' operation than the VTL MB-450 Signature Series II Monoblocks. I won't trust anything else but VTL to deliver this level of proven reliability and performance for my system and my business.

These amplifiers have Active Fault Sensing circuits that make it so simple to diagnose a faulty tube and this also protects the rest of the unit from any possible damage. This feature developed my Luke Manley is not mealy an evolution in vacuum tube technology but a REVOLUTION.

From experience I can tell you this is a very important area of concern when getting up into this power level. Do not under estimate the value in this technology. I have used other large tube amplifiers in the past and the engineers have designed a sonically beautiful and wonderful circuit without even a second thought as to what would/could happen if a tube let go and shorted. In such an event you do not want to be in the same room as the amplifier when it happens and when something goes wrong it always goes wrong in a big way. You really know about it with a blown circuit board in need of repair to prove it and the fright of your life.

Vacuum Tube

Not a hard decision for me to make and all others who prefer music over solid state hearing damaging noise. This is the only sane choice for the mentally balanced amongst us to make.

'Protection' - The reason whey these sell as fast as VTL can make them.

I had to wait 6 weeks for mine to be made.

You will fall in love with these masterpieces and what makes them unique.

Auto Bias / Fault Protection on all Output Tubes via easy to see LED Indicators.

"Comprehensive fault sensing monitors the status of the output tubes, and alerts the user to any adverse conditions. In the case of a problem in any of the output tubes, the amplifier will immediately shut down. The tube fault is indicated on the front panel, as well as by a blinking LED on the top deck next to the tube that caused the fault shutdown, making diagnosis and tube replacement easy.

The logic-controlled automatic bias system is designed to keep the tubes at peak performance and operates completely outside of the signal path. The tube biasing circuit checks and adjusts the tube bias values automatically during the power-on sequence, as well as when the amplifier is at idle (i.e. when no music signal is being amplified.), and drops out of the circuit path when music signal is detected."

New innovative removable side panels for easy vacuum tube access rather than having to remove the entire top cover of the amplifier.

• 20 Amp Power Inlet Socket

• Full Fuse Protection On All Circuits

• Fuses for Main, Logic, Input, Plate & Screen Circuits

• VTL's Super Balanced & Single Ended Inputs

• 12V Trigger for Mute, Mode and Power Functions

• Suer Heavy Speaker Binding Posts

Massive Power Supply Capacitors and VTL's Signature Transformers.

• MODE - Tetrode / Triode Switching

• POWER - On / Off

• MUTE - Mute / Idle Mode

"When the amplifier is in Mute Mode, the output tubes are drawn down to a very low trickle current with noticeably lower heat output to conserve tube life."

 

Sonic Evaluations

The album of choice is 'Echoes' by Pink Floyd (EMI Records- 2001'). With all the extra features of these Monoblocks you might fear that the factory VTL house sound has been corrupted from what we have come to both love and respect. No so. I am told by Luke that all this 'Smart Tube' Technology operates outside of the signal path and reviewing these amplifiers personally I can confirm in no uncertain terms that VTL have succeeded where others have failed.

Before the writing of this review I have found that these Monoblocks require at least a couple of hundred hours on them to really break-in and open up. Please be patient, VTL advise when you are home leaving them on with a music source connected to them and playing with the volume turned down to a low level if so desired. If not run then like they were meant to be used and watch them improve with every hour.

Although the MB-450 model has been around for over 20 years the new Series II generation at the same time produces more controlled bass response with tighter grip and authority down to the lowest octaves which is largely down to a revised power supply which is precision regulated with improved electronic components throughout.

The traditional VTL sound has been improved on and by quite some degree that will be noticeable to all. The openness and transparency has been lifted into the Stratosphere. The imagery, synergy and vocals appear to be produced at a faster pace with no lag time. Very fast sounding amplifiers that combine this trait with liquid valve smoothness. Not overly warm and dark sounding like I have heard from other brands in the past.

Also according to Luke, "The Signature Transformer is an ultra-wide bandwidth, low loss output transformer. The Signature transformer's major strength is that it can deliver the current in the bass, while at the same time maintaining the speed in the high frequencies, dramatically improving the square wave response of the amplifier, and translating to a far cleaner sound."

Although with these amplifiers you have the choice between Tetrode / Triode I have always preferred full power Tetrode mode in all of VTL's designs. Nice for other who might prefer Triode mode to have this feature and choice available to them at the push of a button.

Always run a Balanced interconnect with these amplifiers to take full advantage of VTL's own Super Balanced input circuit. The benefits over single ended operation are considerable and if you are investing in this level of equipment you should really also have a capable line stage with what I would call an essential feature being 'Balanced' circuitry to drive them.

I have put my money where my mouth is for this product and after living with them for quite some time now I am not just happy but thrilled with their performance and am sure I made a great decision in up-grading. I listen to them all day everyday at considerable volume levels without any listener fatigue or strain.

I cannot review these monoblocks without giving fair and detailed mention to the critical line stage driving them. When you are at this level of resolution the synergy between your pre and power combination gets to make a huge difference. This is because when your amplifiers are as revealing and transparent as the MB-450 Signature Series II's the matching of the pre-amplifier or line stage becomes more critical for extracting the most out of what these amazing monoblocks can offer.

The VTL MB-450 Signature Series II monoblocks really need to be run with a matched unit of the same elevated standard to achieve the best results from my testing. The perfect match for these is obviously VTL's very own TL-6.5 Signature Series line stage that according to Luke Manley achieves 90% of the sound quality of it's bigger brother. VTL have advised that from using much of the top tier technology developed when designing from the larger and more expensive two box TL-7.5 Reference Series II the TL-6.5 offers outstanding performance in a more manageable package and at a lower price point and is the perfect partner to the MB-450 Signature Series II monoblocks. So at the end of the day we all get to benefit from the TL-7.5 Reference Series II's limitless R&D budget but way of the brilliant TL-6.5 Signature Series line stage.

Just as the TL-6.5 Signature Series owner benefits from trickle down technology developed from the cost no object TL-7.5 Reference Series II the MB-450 Signature Series II monoblock owner also benefits with parts and technology lifted directly from the companies top of the line Siegfried Reference Series monoblock spare parts bin and pays only a fraction of that purchase price to secure the majority of the performance. It's really great that VTL have provided such truly cutting edge performance level at an affordable market price point with their Signature Series products.

Believe me folks, so good is the performance, texture, and layering of the TL-6.5 / MB-450 Series II combination I do not feel I am missing anything when I listen to my system everyday by not going for the TL-7.5 Reference Series II / Siegfried Reference Series set-up.

To conclude this review I would sum them up as saying they are well endowed with a mountain of headroom and dynamic range to drive the most challenging of loudspeakers with total control authority. The traditional vacuum tube smoothness is there but with an exceptionally fast and transparent soundstage.

The sound presentation I feel is very similar to an O.T.L. amplifier design but blending these qualities together with a traditional hard hitting punch and slam of a large array push-pull 6550C output stage as in the MB-450 Signature Series II is unique and gives the best of both worlds. The single biggest factor for this achievement is the Signature Output Transformers. For those asking why have I spend so much time discussing the transformers in this review the answer is simple. The quality of a vacuum tube amplifier has a huge influence from the output transformer, so naturally this is why VTL have correctly put so much R&D into this area. This is one critical component that effects the entire performance level in all areas of importance.

There is such a high degree of sonic separation between the layers when used with an appropriate line stage and good front end components that you will no longer consciously find yourself listening to the system anymore but you will find that the music takes over and you no longer search for your favourite test disc or L.P. but simply play your favourite artist or album on your system and relax into sonic heaven.

You don't realize how much you have been missing until you try something like this in your system.

Associated review Equipment

• Line Stage:         VTL TL-6.5

• Speakers:           B&W 800 Nautilus

• Cables:              Furutech

• Transport           Wadia 170i

• DAC                   Cambridge DacMagic