MB-185 Series III Signature

MB-185 Series III Signature monoblock amplifier follows the design philosophy of MB-450 Series III and incorporates the same technological upgrades as its high-end models. This Series III platform upgrade is substantial, featuring a completely redesigned signal path and numerous new functions, while retaining all the ease of use of its predecessors, such as automatic tube biasing and comprehensive fault detection capabilities.
Upgrades include a fully balanced differential input stage driving the differential phase separator and a low-impedance push-pull output stage. Furthermore, a shorter, faster, and fully balanced negative feedback loop has been added, achieving zero global negative feedback. This negative feedback loop completely eliminates ringing, maintaining critical phase integrity and data throughput without the need for capacitor compensation. Therefore, this amplifier remains stable even under the most demanding loads.

Another major improvement to MB-185 is the adoption of the EL-34 tube. Acclaimed for its rich, natural, and open sound, the EL-34 tube brings a unique new timbre to this amplifier, further highlighting the cohesion and inner details of the music. The output transformer has been completely redesigned and carefully matched to complement the pure midrange and fast, tight bass of the EL-34 tube.

In addition, the newly added damping factor feedback control function allows users to adjust the amplifier’s output impedance by changing the amount of negative feedback. Impedance can now be precisely set to suit listener preferences and to better control speaker load for optimal performance.

The four possible settings are:

With the lowest damping coefficient, the speaker has the best control and the most natural sound.
Medium – Speaker control is good, but it has some impact on sound quality. HI – Best speaker control, with a slightly larger impact on sound quality, but for speakers that require control, the improvement in sound quality is obvious.
MAX – Maximum damping factor, but noise has a significant impact. Fully balanced differential circuit – can produce a balanced signal at the output even for single-ended signals.
The redesigned fully balanced differential input and driver stage improve signal swing, bandwidth, and stability.
Zero global negative feedback: Shorter and faster feedback loops enable better tone control without phase shift.
Improved speaker load handling enhances signal stability.
This amplifier has absolute stability and requires no capacitor compensation.
Employing a JFET-type current source similar to a vacuum tube reduces noise impact in single-ended mode. A lower impedance output stage improves speaker control.
VTL’s proprietary Signature balanced output transformer significantly improves interleaving and coupling, resulting in wider bandwidth and zero ringing.
User-adjustable DF feedback control allows for adjustments to output impedance and damping factor to achieve optimal matching with speaker load.
Software microprocessor control
Switchable tetrode/triode mode
Automatic bias adjustment and fault detection
Inrush current limiting
Standby mute function; reduces tube current to extend tube life
225 watts per channel in tetrode mode; 140 watts per channel in triode mode
Each monoblock module utilizes eight EL34 or 6CA7 vacuum tubes.
An adjustable regulated power supply for the anode ensures a stable operating point, while independent regulated power supplies for the input and driver stages enhance signal resolution and tonal quality.
This adjustable, precision-regulated bias power supply enhances signal resolution and noise rejection while improving isolation from mains voltage fluctuations; the output operating point remains stable regardless of AC power variations.
An improved automatic bias and fault detection system operates in fully balanced differential mode; the amplifier features comprehensive protection against output tube failure, and precise matching of output tubes is not required.
All capacitors in the signal path are premium Mundorf silver-in-oil types.
Film bypass capacitors are used across the power supply capacitors to achieve superior high-frequency resolution.
Featuring an extruded aluminum alloy front panel, it boasts a luxurious and modern look—available in black and silver.
Rack-mount installation
Sturdy structure, improved ventilation, and lower operating temperatures.
Upgradeable from the Series II factory version.
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 5Ω
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