VTL - Signature Monoblock Amplifiers

Current models include:
•  MB-450 Series III Signature
•  MB-185 Series II Signature

Further information:
•  Review

The VTL Signature Monoblock Amplifiers have evolved steadily since their early inception in the 1990’s, and are the most popular core models in VTL’s lineup. Known for their high power, high performance and ability to drive a wide range of speakers, the Signature monoblocks have won wide acclaim as the best value in high performance tube amplifiers. In 2007, VTL significantly transformed and modernized the Signature Monoblocks by incorporating the “smart-tube” technology derived from VTL’s flagship Siegfried Reference Amplifier, as well a s updating its looks to match the sleek VTL Reference components. Utilizing the auto bias and fault-sensing technology first developed for the Siegfrieds, the new Series II Signature amps are now even easier to use and maintain. Parts upgrades, including portions of the regulated power supply used in the Reference VTL Siegfried monoblocks, contribute to a significant improvement in sonic performance, with greatly improved bass punch and dynamics.

MB-450 Series III Signature Monoblock Amplifier

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:

LOW -- Lowest damping factor, good loudspeaker control, most natural sound.
MED -- Better loudspeaker control, with some impact on sound quality.
HI -- Best loudspeaker control, with a little more impact on sound quality, but on speakers that need the control the sonic improvement is clear.
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.

Feature List:
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.	450 watts per channel in tetrode; 200 watts per channel in triode. Uses eight 6550C 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.
Data Specifications

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MB-185 Series II Signature Monoblock Amplifier

The MB-185 Series II Signature monoblock delivers superior performance at an affordable price. It offers the same technological improvements and cosmetic refurbishment as its bigger brother, the MB 450 Series II, although in this case using six 6550C tubes and a more compact output transformer to make 220 watts per channel. The extensive updates to the Series II amplifier include a revised power supply, SmartTube technology with automatic bias adjustment and fault sensing, and upgraded electronic components. The result is an amplifier with improved dynamics as well as superior speed and transparency at the top end. With its extraordinary agility, the MB-185 Series II is ideally suited for use with planar or electrostatic speakers as well as dynamic speakers with 10-inch or smaller drivers.

Feature List:
VTL proprietary Signature output transformer Software microprocessor controlled Tetrode/Triode Switchable Auto Bias, Fault Sensing Current in-rush limiting Standby Mute function 220 watts per channel in tetrode; 110 watts per channel in triode 6 6550C or KT-88 tubes per monoblock Regulated screen supply and separate fusing	Discrete regulated input and driver supply Redesigned fully balanced input and driver stages High quality audiophile grade coupling caps 12V Trigger and mute input Extruded aluminum front panel with luxurious, modern look – black and silver options available Front panel window of thick smoked glass reveals the glow of multiple output tubes Rack mountable Rigid construction and improved heat ventilation
Data Specifications

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Review

VTL MB-450 Series II Signature monoblock power amplifier, Michael Fremer, January 2008

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