MB-450 Series III Signature Monoblock


Music lovers have long admired the VTL MB-450 Signature monoblock amplifier for outstanding performance at a fair value. The new Series III version of the long-standing MB-450 platform features a complete re-working of the entire signal path. Upgrades include a fully balanced differential input stage driving a differential phase splitter and a lower impedance push-pull output stage with a dramatically improved, fully balanced and enhanced interleaved and coupled output transformer. VTL’s innovative engineering brings the legendary sonic performance of the venerable 450 Signature platform to even greater heights.

The new MB-450 Signature monoblocks gain further sonic benefits with a shorter, faster and fully balanced negative feedback loop, with zero global negative feedback. The negative feedback loop completely eliminates ringing and requires no capacitor compensation to maintain critical phase integrity and information. The result is an amplifier that remains stable even under the most demanding loads.

Adjustable precision-regulated bias and screen supplies hold the output tube operating point constant even under AC and main power supply fluctuations, and stabilizes the critical power supplies yielding tonal stability and sonic integrity especially during complex, dynamic signal conditions.

Another new feature is a user adjustable Damping Factor feedback control that allows the user to adjust the amplifier’s output impedance by varying the amount of negative feedback.  Impedance can now be precisely set to suit the listener’s taste, and to improve control of the loudspeaker loads to deliver best performance.

The 4 possible settings are:

  1. LOW – Lowest damping factor, good loudspeaker control, most natural sound.
  2. MED – Better loudspeaker control, with some impact on sound quality
  3. HI – Best loudspeaker control, with a little more impact on sound quality, but on speakers that need the control the sonic improvement is clear
  4. MAX – Maximum damping factor, but sonic impact is noticeable

Finally, the amplifier has been substantially re-voiced with premium Mundorf silver oil capacitors, for a sweeter, more extended top end and mid range tonality that sounds more relaxed, with better flow and integration. Input stage capacitors are also bypassed.

Even a brief listen to the new MB-450 Series III monoblock reveals the successful implementation of the new technology. The mid bass has more authority and control while the critical midrange exhibits a new effortlessness in reflecting the natural instrumental colors and timbres. This greater sense of ease and control of the critical mid bass and midrange area enables the top end to sound completely natural and unconstrained. The impact of the music’s broad brushstrokes is unmistakable, while at the same time, the listener enjoys the indelible intimacy and micro-dynamics that lay deep inside favorite recordings.

MB-450 III
MB-450 III Back Panel
MB-450 III Back View

Functionality features

  • Fully balanced differential circuit – even single-ended signal produces balanced signal at output
  • Re-designed fully balanced differential input and driver stages for increased signal swing, bandwidth and stability
  • Zero global Negative Feedback
  • Shorter, faster feedback loop for greater tonal control without phase shift
  • Improved handling of loudspeaker loads for greater signal stability
  • The amplifier is unconditionally stable, without the need for capacitor compensation
  • Tube like JFET-type current source for lower sonic impact in single-ended mode
  • Lower impedance output stage for improved loudspeaker control
  • Dramatically increased interleaving and coupling in the balanced VTL proprietary Signature output transformer, for wider bandwidth and zero ringing
  • Variable user-adjustable DF feedback control to vary output impedance and damping factor for optimal matching to speaker load
  • Software microprocessor controlled
    • Tetrode/Triode Switchable
    • Auto Bias, Fault Sensing
    • Current in-rush limiting
    • Standby Mute function; with reduced tube current for increased tube life
  • 425 watts per channel in tetrode; 225 watts per channel in triode
  • Uses eight 6550 or KT-88 tubes per monoblock
  • Adjustable regulated screen supply for stable operating point; discrete regulated input and driver supply for greater signal resolution and tonality
  • Adjustable precision-regulated bias supply for greater signal resolution and noise rejection and improved isolation from mains supply variations; output operating point does not change with AC power fluctuations
  • Improved Autobias and fault sensing system to operate in fully balanced differential mode; amplifier is fully protected against output tube failure; no need for precision matching of output tubes
  • All premium Mundorf silver oil caps in signal path
  • Film bypass of power supply caps for greater HF resolution
  • Extruded aluminum front panel with luxurious, modern look – black and silver options available
  • Rack mountable
  • Rigid construction and improved ventilation for lower operating temperature
  • Factory upgradeable from Series II


pdficon_smallMB-450 Data Sheet

Technical Specifications

Vacuum Tube Complement 8 x 6550 or KT-88, 1 x 12AT7, 1 x 12BH7
Output power
20Hz – 20kHz <2.5% THD
Tetrode: 425 Watts, Triode: 225 Watts
Into 5Ω
Input sensitivity Variable between 1-2V, depending upon DF setting
Input impedance 45kΩ
Load setting
Output load range 4Ω – 8Ω
S/N ratio 450W Tetrode & 200W Triode: -110dB, 120Hz
Power consumption Idle = 300W, Full power = 1000W
Primary mains fuse rating 100/120V = 15A Ceramic Slo Blo, 220/240V = 8A Ceramic Slo Blo
Input fuse 100/120V = 1A Ceramic Slo Blo, 220/240V = 1A Ceramic Slo Blo
Logic fuse 100/120V = 1A Ceramic Slo Blo, 220/240V = 1A Ceramic Slo Blo
B+ fuse rating Plate Fuse – 2.5A fast acting 600V, Screen Fuse – 0.75A fast acting 600V
Dimensions W x D x H 18.5 x 18 x 9 inches (47 x 45.7 x 23 cm)
Weight 93lbs (42kg) per monoblock unpacked, 110lbs (50kg) packed

VTL MB-450 Series III Signature and MB-185 Series III Signature Mono Amplifiers

…“Key to the ‘450’s performance is the foundation provided by its unconditionally stable, fully balanced and heavily regulated circuit topology, the platform on which everything else rests. That stability is what provides its innate sense of order and musical organization, the clarity it brings to musical structure, rhythms and phrasing. With the ‘450s, recordings have a naturalistic perspective and presence that depends on having a place for everything and everything being in that place — not in the clamped, pinched, over-damped and etched style of so many ultra-definition solid-state designs, but in the way that instruments and voices have a natural position and separation.”

“…and the magic of the music survives intact. It’s all about the relationships: the relationship between the notes, the relationship between the players. That’s what the ‘450 IIIs preserve — and preserve so effectively that you can add more and more notes, more and more musicians or voices without the whole edifice crumbling and crashing down.”

“In contrast, the ‘450 has a power margin and sense of musical authority that allows it to handle far more awkward loads with an easy grace, a potent low-frequency weight and extension to make the most of really widebandwidth speakers.”… Read the full review here…

- Roy Gregory, The Audio Beat, November 29, 2014

VTL MB-450 Series III Signature Monoblock Power Amplifier

…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 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…

…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… Read the full review here…

- Michael Fremer, Stereophile, Vol.34 No.4, April 2011

VTL MB-450 Series III Signature mono amps

…It’s this ability to tie the subtleties of time and texture to the solid substance and sheer power of which they’re capable that makes the 450s so special. At the same time as they keep the small and the frankly massive in easy coexistence, they also keep things lucid and articulate.

…what really strikes you is the effortless sense of power, allied to a clear sense of musical direction. Berglund gives us a reading with a real sense of purpose and that’s just what the 450s deliver; there’s never any doubt where this performance is going. The VTLs keep everything pointing the same way, binding all the threads together, building and building them as Berglund demonstrates his mastery over both the score and the forces beneath his baton. Just when you think that the music can’t get any more intense, he releases the pressure in a long, long slide before ramping it up once again into one of the great orchestral climaxes.

…Playing Berglund’s Sibelius Two on the VTLs is a musical tour de force.

…Here is the pot of gold at the end of this particular rainbow – the high-powered valve amp that you can live with AND love. So much music, so few flaws and none of them intrusive, this is an amp that’s finally come of age: More than that, it’s one for the ages. Read the full review here…

- Roy Gregory, Hi Fi Plus, Issue 88, 2012

VTL MB-450 Series 3 Signature Monoblock Amplifier

Read the full review here…

- Jack Liu, Audio Art, Taiwan, January 2011