VTL Mono Power Amplifiers

There are 4 Mono Power Amplifiers in the VTL range, just like their stereo equivalents there is a large variance in both price and performance! Read on!

MB-125 Monoblock

Priced at £6600 per pair the MB-125 represents incredible value for money, running at 100 watts per channel in Tetrode mode (50 W in Triode) it has enough power and current delivery to drive a sensible pair of speakers to a decent volume in a normal sized room.

I’ve heard these running in a system vs 2 well known UK brands who have amplification (in both 1 box and 2 boxes) for similar sort of money to the VTL and terms of musicality, coherence and toe-tapping the VTL had them both beaten before the first chorus of the first song had been played.

Superbly rich mid-range and a sweet top end with clarity and transparency is the sonic signature on offer here.

These are available either in pairs (£6600) or individually (for running in home cinema systems).

  • High energy storage power supply >200 joules.
  • VTL proprietary output transformer
  • Tetrode/Triode Switchable
    • 100 watts per channel in tetrode
    • 50 watts per channel in triode
  • 4 EL34 tubes per channel with individual bias setting for each tube
  • Extruded aluminum front panel with luxurious, modern look – black and silver options available
  • Front panel comes with a window of thick smoked glass where you can see the glow of tubes
More Reading - Audio Esoterica MB-125 Monoblock Amplifiers

MB-185 Series III Signature Monoblock Amplifier

Jumping up to the MB-185 the price of admission increases to £17500, so we’re getting on for 3 times the cost. That said, it’s money well spent if the rest of your system is up to the job.

With the Series III the signal path has been dramatically re-worked to make it is as short and as simple as possible. It contains all of the useful features you’d expect at this level such as auto-biasing and comprehensive auto fault sensing so you’ve no doubt if a valve may need replacing.

Upgrades with Series III include a fully balanced differential input stage driving a differential phase splitter and a lower impedance push-pull output stage. Also new is 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.

Another significant change to the MB-185 is the switch to well respected EL-34 tubes. Long admired for their rich, natural and open sound, the EL-34s bring a distinctive new sonic signature to the amplifier that emphasises the integration and inner details of music. The output transformer has been completely redesigned and carefully matched to complement the midrange purity and quick, taut bass of EL34s.

As with the S-200 and S-400 we also get the 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. Medium – Better loudspeaker control, with some impact on sound quality
  3. High – Best loudspeaker control, with a little more impact on sound quality, but on speakers that need the control the sonic improvement is clear
  4. Maximum – Maximum damping factor, but sonic impact is noticeable

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
  • 225 watts per channel in tetrode; 140 watts per channel in triode
  • Uses eight EL34 or 6CA7 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
More Reading - Roy Gregory, The Audio Beat (VTL MB185 Series III & MB450 Series III)

MB-450 Series III Signature Monoblock Power Amplifier

The MB-450 has frequently been classed as THE reference VTL Power Amplifier and for good reason. Priced at £20,000 for a pair they are one of my personal favourite amplifiers of all time. They all but disappear from the presentation, delivering perhaps one of the most ‘live’ sounding musical experiences I’ve come across to date.

They really engage and are incredibly expressive with a huge amount of power on tap, compared to the MB185s they will drive a much bigger and more demanding speaker with a lot more authority and scale.

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 very clever 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 settings are:

  1. Low – Lowest damping factor, good loudspeaker control, most natural sound.
  2. Medium – Better loudspeaker control, with some impact on sound quality
  3. High – 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

Don’t underestimate this feature, it can be incredibly useful and you will no doubt find that one of the 4 settings will sound dramatically better than the other in your sysyem; which is the right one depends entirely on the speaker and to a lesser extent how that speaker interacts with your room. If you have large speakers, or speakers that are incredibly difficult to control (big bass drivers – like B&W 801s for example), having it set to high or max is better. But in most instances Low and Medium are the optimal settings for maximum sound quality, but it really does depend on the speaker.

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.

  • 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
                     More Reading - Roy Gregory, The Audio Beat (VTL MB185 Series III & MB450 Series III)
                                                   Hi-Fi Plus Magazine (MB450 Series III)
Siegfried Series II Reference Mono Power Amplifier
The Siegfried is the VTL flagship amplifier, the absolute pinnacle in tube design and technology. The original Siegfried launched in 2003 and was the first valve amplifier in the world to feature Auto-Bias and Fault Sensing.
The Siegfried has a magnificent reputation and a performance second to none. It’s one of those products that you often see in photographs online showing true reference high end systems. A number of world-class loudspeaker manufacturers use a pair of Siegfrieds as their reference point for voicing their designs.
The reviews that the Siegfried has received the world over speak for themselves as well, to quote Michael Fremer from Stereophile magazine – “Remarkably quiet, wideband, as linear and tonally neutral as the best solid-state amps, and with just a kiss of the effortlessness tube lovers find so addicting, the VTL Siegfried II was as neutral and as uncolored as any tube amp I’ve listened to.”
If you want to get to the heart and soul of the music the Siegfrieds are the amplifiers to do it. Regardless of what genre of music you favour the Siegfried delivers so much clarity, transparency and raw emotion. With 650 watts per channel in Tetrode mode (330 in Triode) they offer effortless control over whatever speaker you choose to partner them with, each mono block packs in a dozen of the superb 6550 valves. KT88 valves are available as well as a cost option. Sonically they are a smooth and sweeter than the 6550 which offer more dynamics and punch.
The fault sensing on the Siegfrieds is superb, the LED display will inform you if a valve has blown, but it won’t stop playing music. You can monitor tube hours, internal temperatures, mains voltage. It can even be connected to a computer to generate a report for all the faults/issues it has ever sensed.
Perfect embodiment of modern and ancient technology being used together harmoniously!
Quite possibly the best mono power amplifiers in existence!

The new Series II version of the renowned Siegfried 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.

The new Siegfried Reference 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 plate, screen and bias 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 settings are:

  1. Low – Lowest damping factor, good loudspeaker control, most natural sound.
  2. Medium – Better loudspeaker control, with some impact on sound quality
  3. High – 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

As previously mentioned Low and Medium are the most popular settings, although it will vary from user to user depending on the speakers being used.

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.

  • Fully balanced differential circuit – 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 any capacitor compensation.
  • New 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 Reference 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
    • Fully bi-directional RS-232 control
  • 650 watts per channel in tetrode; 330 watts per channel in triode
  • Uses twelve 6550 or KT-88 tubes per monoblock
  • Adjustable precision-regulated plate and screen supplies 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
  • Precision regulated B+ and screen supplies
  • Rigid construction and improved ventilation for lower operating temperature
  • Factory upgradeable from Series I
More Reading

VTL Siegfried Reviews Page

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