MB-185 Series III Signature Monoblock


Following the footstep of the MB-450 Series III, the MB-185 Series III Signature monoblock has gone through the same technological improvements as its bigger brother. The upgrade to the Series III platform is extensive with a complete rework of the signal path and new features added while retaining all the user friendliness of the previous model such as automatic tube biasing and comprehensive fault sensing.

Upgrades 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 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 emphasizes 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.

There is also a new 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
MB-185 III
MB-185 III Back Panel
MB-185 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
  • 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


pdficon_smallMB-185 Data Sheet

Technical Specifications

Vacuum Tube Complement 8 x EL34 or 6CA7, 1 x 12AT7, 1 x 12BH7
Output power
20Hz – 20kHz <3% THD
Tetrode: 225 Watts, Triode: 140 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 225W Tetrode & 140W Triode: -90dB, 120Hz
Power consumption Idle = 270W, Full power = 550W
Primary mains fuse rating 100/120V = 12A Ceramic Slo Blo, 220/240V = 6A 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 – 1.5A 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 85lbs (38.5kg) per monoblock unpacked, 100lbs (45.4kg) packed

MB-185 Series III | Sound Stage Australia

“The sense of live musicians in their room and now in yours is again spookily real … as in being at a live performance, detail is imminent as a naturally occurring aspect of the artists at work in a specific acoustic space and time. It is the actual physical presence of the amps themselves that can never be discerned. The VTLs instead ultimately give primacy to and serve wholly the performer and the performance. It is as if the glass fascia on the front of the amplifier’s casing is a window into that musical event, the tubes illuminating that performance, with seemingly infinite colours and washes of tone.”

”The VTL MB-185 Series III Signature amps, especially when mated with the highly sympatico VTL 6.5 Series II Signature tube based preamplifier, equally distinguished by its accurate tonal balance and rhythmic prowess and linearity, results in a system of amplification that has managed to bring out the best in every speaker I have to date hooked them up to, from big Wilson Sasha 2s to little Harbeth monitors. No glare, no listener fatigue. Just a whole lotta musical satisfaction going on.”

Read the full article here…

- Peter Katsoolis, “VTL MB-185 III Signature Monoblock Amplifiers,” SoundStageAustralia.com, August 2017

The 12th Annual Positive Feedback Writers’ Choice Awards for 2015 – The Best of the Best!

VTL MB-185 Series III Balanced Signature Amplifier

MB-185 III Award
I heard a large variety of gear this year, having attended both T.H.E. Show Newport, actually located now in Irvine, and RMAF in Denver. Mentally rewinding all that now, and searching for common denominators between this year’s models and previous encounters, certain touchstones emerge. You can tell a lot about high-end manufacturers by the company they keep. People who design and produce high-quality audio products obviously want to partner with other products that will make them sound great in a show setting. In other words, it is not a random coincidence that several of the systems I have connected with most positively over time at varied venues contained electronics from VTL Amplifiers Inc. I admire audio companies with real track records, as Luke Manley has been creating since 1987 with Vacuum Tube Logic. The company name says it all. VTL’s focus has been on creating very high-quality tube-based amplification gear from the get-go, with those designs refined over time.

At the 2015 RMAF I spent some time with the VTL MB-185 Series III Balanced Signature Amplifier. These hefty looking monoblocks put out 140wpc in triode mode, or 300wpc in tetrode, into 5 ohm loads. That is a lot of great tube juice, capable of driving loudspeakers with aplomb, even the tough customers load-wise. And the VTL’s do this with a S/N ratio of -90dB. One of the updates in the current model is the utilization of EL34 tubes, 8 per channel. In my experience this tube type delivers a punchy and strong sound, almost ‘poppin’ if you will. And this is in line with one of VTL’s design goals, as stated clearly on their website—power. These are not your aunties little flea-circus monoblocks, but some Big Dog units that brought the Wilson loudspeakers I heard them driving to heel. They can bark, but they can also purr- I heard the most minute and delicate textures, as well as white-hot fireworks, depending on the music. In the RMAF room the VTLMB-185’s were partnered with their VTL preamplifier siblings- the VTL TP-6.5 Signature Phonostage ($12,000), and the VTL TL-6.5 Series II Signature Linestage preamplifierlifier ($15,000). This is not meant as a full-scale review, so I refer readers to the VTL website for more detailed information: https://vtl.com

Read the full article here…

- Sasha Matson

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

…For my musical tastes and in my system, the ‘185 IIIs’ combination of musical grace, structural insight and articulation, their ability to reveal the interplay of musical phrases, textures and tonality, their sheer rhythmic dexterity and effortless ability to track changes in pitch and tempo, make them a musical joy.”

“The ‘185s deliver a natural perspective,a beautiful sense of acoustic space … and a beautifully separate and focused solo instrument. They allow Yepes his full expressive range, his notes and phrases their full shape and spacing, a master class in lucid precision. But they also embrace the sudden shifts in dynamic density that allow the music to jump and surprise, they traverse the astonishing changes in rhythm and tempo without hesitation or restraint.”

“This is an EL34 amp done right; in fact, make that done very right indeed!”… Read the full review here…

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

VTL MB-185 Series 3 Signature

…After you listen to the MB-185 Series 3 Signature amplifier, you will not be thinking about a comparison between a solid state amplifier versus a tube amplifier. The reason is that the sound of this amplifier very simply shows you what live music is all about. There is no artifice, no individual sonic character that stands out. Whatever music you are listening to, the MB-185 will give you a faithful representation… Read the full review here…

- Jack Liu, Audio Art, Taiwan, Nov. 2012

VTL MB-185 Series III

… I have to say that we probably have before us the best VTL “finale” (the best power amp) ever. Obviously I don’t want to say that the MB-185 trumps comprehensively the Siegfrieds which cost so much more (which remain possible for so few of us). Let’s just say that I am beyond curious to hear an eventual version of the Siegfrieds provided with the same improvements … But as I think again, this may be something that would be better not to know at all! Surely I must let VTL know how much I appreciate how it has constantly improved a project that it began a good thirty years ago while remaining faithful to the genial simplicity of the original circuit, introducing in various phases improvements in the ease of use, in dependability, in the maintenance of the tubes themselves (I’m referring here to VTL’s autobiasing), and this time (with the MB 185) reaching theoretical perfection for an tube amplifier of great power with balanced circuitry and no global feedback.

…the MB-185s beat my beloved 225s right across the board. The 225s have no superiority to speak of compared to the 185s. The latter have better bass, quicker with better damping, the mids sound more precise, and the highs are lighter and airier. I prefer tetrode operation, but some may still find the triode capabilities of the 185s to their taste. I played with the feedback options but went back to the default immediately. Nevertheless the opportunity VTL provides listeners to intervene and vary the amplifiers’ performance subtly (via the DF switches) are commendable. Read the full review here…

- Marco Benedetti, Audio Review, Italy, No. 336, Sept. 2012

CES & THE Show 2011 | Hot Product

Call them “retro” for their use of EL34 output tubes, but VTL’s new MB-185 Signature Series III monoblocks sounded anything but old school driving a pair of Avalon Indra speakers. All the treble and midrange splendor of EL34s were present, along with potent bass drive. Read the full report here…

- March Mickelson, The Audio Beat, CES 2011 Show Report - Hot Product

CES & THE Show 2011 | Baubles, Bangles & Beads

…The ‘450s’ new little sibling, the ‘185, is based on the ‘450 but reworked to make the most of the EL34 power tube. A well-made EL34 is one of the gold standards for high-end, hand-wired guitar amplifiers and has a delightful sweetness and delicacy that, backed by a traditionally stiff and overbuilt VTL power supply, yields nothing in the way of traction and oomph in the lower ranges. The ‘185-anchored system was immediately inviting, very much a “pour a glass of wine, put on some tunes and relax” system. I can’t imagine any real music lover not falling in love with the perfectly wonderful sound this system produced. Read the full report here…

- Paul Bolin, The Audio Beat, CES 2011 Show Report