VTL MB-450 Series III Signature Review
VTL is a legendary Californian tube specialist. It is already delivering the third generation of the MB-450 III Signature monoblocks, which pump 425 watts into the speakers. 7Review has tested them.
by Tom Frantzen
An amplifier, also called a power amplifier or current amplifier, converts the signal voltages of the preamplifier into power capable of driving a loudspeaker. Such power amplifiers are in most cases designed for stereo, i.e., two-channel playback. For higher power demands, they are also available as monoblocks. In this case, an amplifier is designed exclusively for one channel, which ensures a particularly generous output power. High-power amplifiers in tube technology are traditionally rather rare. Usually, 100 watts is the limit. Because the costs to achieve even this value are relatively high compared to the semiconductor world. But exactly such mono power amplifiers and powerhouses we have in front of us with the VTL monos, which are presented here in the “Signature” version.
Monoblocks, as banal as it may sound, have a practically infinite channel separation—and this has a positive effect on plasticity and spatial imaging. Thus, such monos are considered the royal road. The VTL brand is a legend. The US manufacturer was founded in 1987, with David and son Luke Manley initially working together. The brand Manley Laboratories, primarily responsible for professional studio technology, was added later, and after a business split, Luke Manley eventually continued VTL and the now unfortunately deceased David Manley continued Manley Laboratories. So, Manley primarily supplies music production and VTL the reproduction. The headquarters of both companies, including production, are now located in Chino, California.
“Mono power amplifiers with such immense power based on tubes are a rare species.”
With a tube-driven amplifier weighing a hefty 42 kilograms and a price per unit of just under $24,000, a feeling of awe naturally sets in. This still applies after almost 30 years as a tester and even more so when dealing with the third incarnation of such a legend. From a circuit point of view, the present monoblock can be traced back to the early 90s and has been called the MB-450 since 1996. With the Series II Signature, the “Smart Tube” technology derived from the reference monoblocks Siegfried was introduced into the devices in 2007.
This refers primarily to the processor-controlled automatic self-analysis and bias adjustment of all tubes. Furthermore, the MB-450 monos “inherited” the precision-regulated power supply and the overall revised circuit with the highest quality components, with a fully symmetrical input stage and extremely elaborate output transformers from their siblings costing almost $144,000. With the latest Generation III, an improved, variable negative feedback loop for amplifier control was added. Each monoblock MB-450 III Signature can be operated with a total of eight standard output tubes KT88 or 6550 at your choice. Driven as a tetrode (four-pole)—more precisely as a “tube type with four electrodes”—the VTL pumps a continuous 425 watts into the speakers, and with the same tube operated as a triode (three-pole), it delivers 225 watts, measured at 2.5% distortion and 5-ohm load. The switching can be done during operation on the front left, which is rather rarely handled in this way with switchable amplifiers. 7Review recommends, however, for reasons of caution, to at least significantly reduce the listening volume.
Variable Damping Factor
In addition to the tube configuration, the damping factor on the MB-450 III Signature can be adjusted in stages between LOW, MED, and HIGH. The very useful auto-bias circuit ensures that the pre-matched KT88s in the test device work optimally together, so that on the one hand a maximum of low-distortion power and on the other hand a minimum of wear occurs. So you don’t have to worry about anything; the amplifier checks its specifications itself during the startup phase after switching on and adjusts if necessary. Borrowing from Rudolf Diesel, one could well call the step-by-step startup phase indicated by blinking LEDs a “Manley” memorial minute, but of course, this “soft start” also benefits the operational safety and lifespan of the tubes. You should allow the powerhouse one or two minutes. You don’t have any choice anyway. Triode fans must be very strong now. Of course, we are well aware that a tube amplifier as a triode often sounds better, more colorful, softer, and more atmospheric, or at least can sound so, than in the more complex pentode or tetrode mode. However, the VTL amp has twice the power as a tetrode.
In the case of the fantastic B&W 801 D4, however, it was audible that even the nominal 225 watts as a triode can sometimes become scarce. In tetrode mode, however, the VTL has superb control over this speaker, especially when the transistor-equipped (!) Accustic Arts PRE-AMP V in the large 7Review listening room, as one of the best preamps, prepared the work.
Dream Team in the Listening Room
This preamplifier delivered real punch and “grip” in the bass, while the congenial strength of the VTL monos lay in the radiance and colorfulness as well as in the emphatic power of the extremely agile mid-high frequency reproduction, and was able to unfold without restraint. We have never heard such a powerful yet controlled bass from a tube. The fine detail reproduction and sovereignty of the VTL is absolutely exemplary; the stage is illuminated extremely spaciously and plastically, and the most delicate individual events, such as facets in Tori Amos’s voice, are wonderfully worked out even at high levels without breaking up the context. Textures are and remain traceable in all areas of the spectrum. This is undoubtedly world-class, and depending on preferences, one or the other will choose these tubes because of this spectacularly resolved, powerful intonation of the mids, even if, for example, the transistor power amplifier from Accustic Arts kept the bass on a leash just a jot better. Here, the decision on what one prefers becomes very, very difficult. However, the control of the VTL over the B&W remains absolutely phenomenal for a tube!
The influence of switching the damping factor on the large VTL is less than the tube configuration but still audible. It can be adjusted in three variants using two toggle switches: LOW, MED, and HIGH. Of course, this is a welcome means to further fine-tune the amplifier and transducer, which are a sensitive pair for music reproduction. And this can be of particular importance, especially with tube amplifiers. The offer is honored; it is realized by very few tube devices—the Accustic Arts offers something similar as a transistor power amplifier. However, we wonder a bit about the sense of positioning these toggle switches inside the VTL power amplifier. Because you have to remove housing parts (protective grille) to adjust them. With both monos together, we’re talking about 24 screws here.
But we actually found the middle position to be universal enough to leave it there in most cases and with most speakers. Usually, you’ll try this once with your transducers and optimize it for your own system; in retail or test operations, it would be better otherwise. We also find the fiddling with the tight speaker terminals a bit tedious but don’t want to overemphasize that either, as you don’t have to or “may” do that often as an owner, and other power amplifiers rarely “shine” here. The VTL powerhouses are delivered with unmounted power tubes. The dealer or proud new owner can take care of that themselves. In the test sample, eight KT88s per channel/monoblock are to be used; 6550s are alternatively possible later. The VTL power amplifiers are extremely well protected. Even a cursory glance at the “armada” of fuses on the back of the Californian amplifier reveals that. They protect the considerable investment made from damage that could occur in the event of mishandling, short circuits, overheating, direct current, or the like. VTL’s confidence in its own qualities is reflected in five years of warranty upon registration; for the tubes as wear parts, VTL gives half a year warranty.
That might sound more threatening than it is. Because that a tube “dies” is rarer than one might think, and it takes much longer than one might fear. Moreover, the more common types do not cost a fortune and are optimally protected here by design. So everything is fine. In terms of measurement technology, the VTL delivers few surprises besides the extremely high output power. The distortion level is moderate for a tube amplifier, but the noise is even outstandingly low at well over 90 dB! The damping factor is somewhat low, and unsurprisingly, the high idle power consumption of 272 watts—per monoblock, of course—is noticeable. The power amplifiers undoubtedly make a noticeable contribution to heating the living room, which is not unpleasant, at least in winter.
Power and Glory
All in all, it remains to be noted that these VTL monos, with a suitable preamplifier and top transducers, are among the best we’ve ever had in the 7Review listening room. Of course, one must also attest that this is due not least to the immense power, which is extraordinary for tube amplifiers and is quite helpful when driving even more difficult and demanding speakers. In the case of particularly demanding transducers, a tube amplifier rarely comes in “pole position.” That’s a pity when you consider what tube technology can achieve here, especially in the quality of a particularly agile and powerful, expressive midrange reproduction. In this case, however, one must once again state that power apparently can be replaced by nothing but even more power. This applies especially to larger rooms and, as mentioned, “hungry” speakers. And it pays off immediately there. These are extremely fascinating and absolutely outstanding sounding amplifiers—wow!
Specs
- Type / Price Class: Mono Power Amplifier (Tube) / Over €10,000
- Website: www.vtl.com
- Price: €39,000 (pair)
- Dimensions (W x H x D): 46.5 x 23.5 x 46.5 cm
- Weight: 42 kg
Evaluation Breakdown
Sound (55%)
- Rating: 9.3/10
- Description: Expressive, colorful, finely resolved with good grip, dynamic, three-dimensional, and lively.
Measurements (25%)
- Rating: 7.9/10
- Power Output per Channel (4/8 Ohm at 3% THD): Very Good (305W)
- Impulse Power at 4 Ohm (1 kHz): Very Good (339W)
- Intermodulation at 5W: Good (0.17%)
- Damping Factor at 4 Ohm (63Hz / 1kHz / 14kHz): Very Low (4/4/2)
- Channel Separation (dB): Very Good (Mono)
- Upper Frequency Limit (kHz): Very Good (>80kHz)
- Distortion Factor at 5W (%): Good (0.081%)
- Signal-to-Noise Ratio at 5W (dB): Very Good (93dB)
- FFT Spectrum: Good
- Power Consumption at Idle (W): Very High (272W)
Features (10%)
- Rating: 8.8/10
- Build Quality: Good
- Number of Inputs (Cinch/XLR): Very Good (2, both switchable)
- Color Options: Only one available
- Triode/Pentode Switchable: Yes
- Bias Adjustable or Auto-Bias: Yes
- Tube Replacement Possible: Yes
- Hard Power Switch: Yes
Usability & Handling (10%)
- Rating: 8.8/10
- Device Operation / Display: Good
- Manual Quality: English only
- Warranty: 5 years (registration required); 0.5 years for tubes
Final Test Result
- Overall Rating: 8.4/10
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