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:
- 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
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 aluminium 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
20Hz – 20kHz <3% THD: 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