VTL MB-125 MonoBLoc AMpLifiers

on test
VTL MB-125
Monobloc Amplifiers
V
acuum Tube Logic, better known
as VTL, has been in the business of
making outstanding valve amplification products for around a third of a century.
It was back in the early 1980s, in South
Africa, that the father and son team of David
and Luke Manley produced quality valve amplification pitched at local professional film
and music recording studios. From there,
*David Manley died of a heart attack on
December 26, 2012, at the age of 73, in
Varrennes-Jarcy, France, where he had
moved to live with his sixth wife, Veronique.
54
word spread and soon the Manleys crossed
the ‘pond’ and started building amplifiers
for the domestic market in Europe. Further
success, especially after 1986’s Consumer
Electronics Show, saw the company move
to the United States where, for the first
time, they embarked on full-scale production on a global scale. The MB-125
reviewed here, however, is entirely the work
of Luke Manley, David having left VTL in
1993 to concentrate on his eponymouslynamed company, Manley Labs, which is
now owned and operated by David’s fifth
wife, EveAnna Manley. (*See left.)
Keep It Simple
As the entry point to VTL’s line of amplifiers,
the MB-125 monoblocs are almost diminutive by way of contrast with the high-end’s
almost ubiquitous ‘bigger is better’ approach. Be that as it may, but the unpretentious MB-125s are nonetheless built to
very high standards. And the amplifiers are
as simple as they are elegant. The nicely
curved brushed aluminium fascia features a
large central smoked glass window—which
becomes a viewing porthole to the innards
and the glowing glory of the EL34 power
and 12AT7 signal valves within.
vtl mb-125 monobloc amplifiers
On TEST
Power Output: Single channel driven into
8-ohm and 4-ohm non-inductive loads at
20Hz, 1kHz and 20kHz using tetrode mode.
Other than the window to valve goodness, the faceplate’s only mar from total
barrenness is a power switch that’s flanked
by a small blue LED. Equal simplicity applies to the sparsely-populated rear panel
where only a single-ended RCA provides
signal connectivity, an IEC socket provides
the 240V a.c. connection and a very nicely
machined pair of binding posts will cater
for your speaker cables. A toggle switch
provides the option of running the amplifier
in either low-powered triode or full power
tetrode mode. Experimentation here is
advised as the sonic differences between
each mode will vary depending on speaker
load and character. Generally, it’s thought
that for a purer, perhaps more full-bodied
presentation, you’d choose triode mode
while more punch and dynamics can be had
by running in tetrode mode. But as they say,
your mileage may vary…
The MB-125s are specified as being capable of 55-watts and 100-watts into 5Ω in
triode and tetrode modes respectively. Frequency response in both modes is claimed
to extend from 20Hz to 20kHz at ±0.1dB.
The power specifications derive from an array of four EL34 valves per monobloc which
are driven by two 12AT7s. The MB-125 is
quoted as being able to drive loudspeaker
loads right down to 2Ω. Input impedance is
a high 145kΩ which makes these amplifiers
suitable to run with almost all preamplifiers
I’m aware of.
Overall, the ‘fit ‘n finish’ is of a very
high standard and the units feel substantial
in terms of their weight and their torsion
strength. Care should be taken when lifting the units as they’re disproportionally
weighted towards the rear (where the substantial custom transformers are housed).
Although I’ve listed the warranty as being
two years, if you register your product with
VTL’s Australian distributor, Advance Audio,
it will extend the warranty period (on the
amplifier only) to five years. The valves are
warranted for only six months.
On a side note, VTL is not only about
high level signal amplification. The company’s two-box TL-7.5 preamplifier, now in
its MkIII iteration, has received universal acclaim as being of reference level and among
the very best available. Similar technologies
apply to the preamps on lower rungs, so
the former leading to long-term bliss and
the latter to an expensive and bumpy seat
in the gear-swapping carousel.
VTL’s MB-125 has the reputation, pedigree and specifications to work with an
almost universal set of speakers but, darn
it, they sounded outstanding with the ‘onpaper’ difficult-to-drive Wilson Sasha Watt/
Puppies. Here were two simpatico components that greeted each other, shook hands,
and went about producing some of the best
sound I’ve heard.
The MB-125s would have to be amongst
the sweetest yet most hard-driving valve
amplifiers given their moderate power
rating (I also run a 750-watt solid-state
monster—so we’re talking about gravitating
from the sublime to the ridiculous).
VTL MB-125
Monobloc Amplifiers
Newport Test Labs
Newport Test Labs
For a purer, perhaps more full-bodied
presentation, you’d choose triode mode...
Power Output: Single channel driven into
8-ohm and 4-ohm non-inductive loads at
20Hz, 1kHz and 20kHz using triode mode.
very sound one-brand pre/power combinations are on offer.
On a size note, each of the VTL MB-125
amplifiers measures 400×300×180mm
(WDH) and weighs 22kg.
A Perfect Match?
In the world of audio, where the pursuit of
sonic excellence is achieved via both scientific and creative avenues, the concept of
synergy can be either a blessing or a curse.
Insert a new component into an existing
system and it could be heaven or hell, with
Brand: VTL
Model: MB-125
Category: Monobloc Power Amplifiers
RRP: $8,495 per pair
Warranty: Two Years (Six months on valves)
Distributor: Advance Audio Australia
Address: Unit 8, 509–529 Parramatta Road
Leichhardt NSW 2040
T: (02) 9561 0799
E: [email protected]
W: www.advanceaudio.com.au
Triode & Tetrode
Magic midrange
Chino not China!
Power consumption
Runs hot
LAB REPORT: Turn to page 58
Test results apply to review sample only.
55
ON TEST
vtl mb-125 monobloc amplifiers
Rarely have I experienced such a total lack
of grain or etch ... and there was plenty of
magic in the all-important midrange.
Power Output: Single and both
channels driven into 8-ohm and
4-ohm non-inductive loads at 20Hz,
1kHz and 20kHz using pentode and
triode modes. [VTL MB-125]
The amps exerted impressive control, not
only over the twin high-power 203mm
woofers, but with the overall sonic presentation, especially in the dynamic contrast
domain. Demanding musical fare was just a
walk in the park for these amps and, much
like the many other US-based valve amps I’ve
reviewed in Esoterica, the VTLs managed to
tread a space where profound detail, resolution and instrumental separation were the
bedfellows of warm, full-bodied, yet quite
fast and furious sound. Drums and percussion, toms and kick in particular, displayed a
‘roundness’ and a vigorous attack with-
56
out excess bloom or boom—just a more
expressive, less-dry presentation than some
high-damping solid-state amplifiers, but one
just as powerful-sounding and, in this case,
more satisfying. In that last sense, the MB125s sound like far more powerful beasts
than their specifications would suggest. And
that, surprisingly, was in triode operation, my
preferred mode of listening, with the tetrode
mode bringing a bit more punch but at the
same time losing some ‘bloom’ and magic in
the midrange… but only a tad, mind.
And there was plenty of magic in the
all-important midrange. Whether vocals or
brass, or the lower violin and upper cello
notes—and so much more—the MB-125
monos were always resolute and sweet.
Rarely have I experienced such a total lack of
grain or etch. And again, stressing the solidity of the images, the large sense of space,
the superb instrumental separation and the
surprising dynamic modulation. In my experience, some amplifiers at this price-point
exhibit a limitation of some form; sometimes
it’s a tad too much bass bloom (possibly associated with cost-savings and compromises
in the transformer design) or a colouration or
lack of transparency in the mids or highs
(the association there may be related to
circuit and component compromises). The
MB-125s just played music; always involving,
always utterly listenable.
Conclusion
In my opinion, having at least one item in the
system chain sporting valve circuitry brings
the magic. The crowded Australian market
offers plenty of valve amplifiers, and certainly
a whole host of budget fare in over-the-topbling livery from China, but what the VTL
MB-125 monos offer is understated elegance
mixed with solid engineering and all-American manufacturing (in Chino not China).
Few amplifiers have had the impact or
had my reference system singing to the
triumphant levels as the MB-125s. Call it
synergy, within the microcosm of my reference system, or call it all-round potential
excellence in the audio world at large. Sir or
madam, one thing is for sure; shopping at
this price-point and not trying VTL’s MB-125s
is totally at your peril because, in the world
of the high-end, these VTL MB-125 monoblocs are one hell of a bargain.
Edgar Kramer
TEST RESULTS ON PAGE 58
Lab Report
vtl mb-125 monobloc amplifiers
Laboratory Test Results
One reason audiophiles (and musicians) like
valve amplifiers is that they overload very
gracefully… so gracefully that it’s difficult to
perceive they’re overloaded at all. Whereas
solid-state amplifiers go straight into hard
clipping at which point they suddenly
generate (literally) hundreds of high-level
odd- and even-order harmonic distortion
components, valve amplifiers clip ‘softly’
and, when they do, generate only a few,
low-order harmonic distortion components,
many of which sound so pleasant to the ear
(being predominantly low-order and evenorder harmonics) that it’s difficult (perhaps
impossible) to hear they’re overloading at
all. This ‘soft clipping’ effect also makes it
difficult to measure the exact output power
of valve amplifiers, because soft clipping
is also difficult to observe visually on an
oscilloscope screen, whereas hard clipping
is instantly visible. As a result, the power
output figures measured by Newport Test
Labs were not taken at clipping, but at the
level where THD exceeded 3.0%.
If you’re comparing the tabulated figures
with the manufacturer’s specifications, you
should note that Newport Test Labs used
standard 8Ω and 4Ω test loads during the
measurements, whereas VTL for some
reason used 5Ω test loads when compiling
its specification sheet, so the figures are not
directly comparable… though 4Ω is close
enough to 5Ω that any differences between
using one rather than the other would
mostly be academic. So I’ll start with the 4Ω
loads and, using its high-output (tetrode)
mode, the VTL MB-125 delivered 81-watts
58
(19.0dBw) at low and midrange frequencies, but managed only 60-watts (17.8dBw)
at 20kHz. In its low-output (triode) mode,
the VTL MB-125 was measured as delivering 40-watts (16.0dBw) at low and mid
frequencies, and 20-watts (13.0dBw) at
20kHz. As you can see from the tabulated
results, the power output figures were not
substantially different when the amplifier was driving an 8Ω load. Although the
amplifier falls short of VTL’s ratings, it didn’t
fall much short, in fact it was just 1.4dB shy
of spec in triode mode and just 1dB shy in
tetrode mode (using the result at 1kHz as
the reference).
The frequency response of the VTL
MB-125 was extended, reaching out
to 94kHz (–1dB) and a fraction further
(110kHz) if we look at the 3dB downpoint.
At the low-frequency end of the spectrum,
the VTL was 1dB down at 12Hz and 3dB
down at 7Hz. This puts the ‘normalised’
response at 12Hz to 94kHz ±0.5dB, or
7Hz to 110kHz ±1.5dB. Within the audio
band, the response was much flatter again,
at you’d expect, and as you can see from
Graph 5 (ignore the tiny ripples on the
traces on this graph, which were the result
of some mains-frequency hum creeping
into the measurements). Into a standard
resistive laboratory load (the black trace
on the graph) you can see the VTL MB125’s frequency response almost tracks the
0.00dB reference line from 20Hz to 10kHz,
then rises to be 0.05dB ‘high’ at 20kHz.
(The response continues to rise to peak at
50kHz, before rolling off to 94kHz.) This
puts the normalised audioband frequency
response of the VTL MB-125 at 20Hz to
20kHz ±0.02dB.
When the VTL MB-125 was connected
to a load that simulates that of a typical
two-way loudspeaker (the red trace on
the graph) you can see that its frequency
response was not nearly so linear as into
the purely resistive load, but the overall
response was still measured at 20Hz to
20kHz ±0.3dB, which is an excellent result.
(The vertical scaling of this graph must be
borne in mind: it’s quite extreme, with the
tops and bottoms indicating +1dB and –1dB
respectively.)
Graphs 3 and 4 show the output spectrum of the VTL MB-125 when driving 8Ω
and 4Ω loads at an output of one watt,
respectively. As you can see, distortion
is very low for a valve amplifier. Into 8Ω
loads, there’s a second harmonic at –75dB
(0.0177% THD), a third at –80dB (0.01%
THD), a fourth at around –98dB (0.0012%
THD) and that’s it (the ‘spike’ below 16kHz
is a measurement artefact, and should be
ignored on all the graphs on which it appears). When driving 4Ω loads, the level of
the second harmonic increases to –68dB
(0.0398%), the level of the third harmonic
to –70dB (0.0316%) and the level of the
fourth to around –94dB (0.0019%) and a
fifth harmonic appears at around –99dB
(0.0011%). These distortion levels are all
quite low, as you can see, but also, adding
second harmonic distortion is musically the
same as adding a second note an octave
above, which the human ear finds ‘pleasant’ and adding a third harmonic is musically equivalent to adding a fifth above, which
vtl mb-125 monobloc amplifiers
again results in a sonically pleasing result.
The noise floor on both graphs shows that
there’s considerable low-frequency noise
in the output, likely mains-related, which
accounted for the VTL MB-125’s relatively
high unweighted noise figures.
dBFS
0.00
Distortion at high power output levels
was high, as you can see from Graphs 3
and 4, which show output at 55-watts into
an 8Ω load (Graph 4) and at 70-watts into a
4Ω load (Graph 5) both graphed using the
VTL’s tetrode mode. You can see that into
Newport Test Labs
-20.00
Lab Report
an 8Ω load, except for the third harmonic,
all the other harmonic components were
more than 70dB down, so each contributed
less than 0.0316% distortion to the total.
Into 4Ω loads, save for the third harmonic
at around –53dB (0.22%), the first five
dBFS
0.00
Newport Test Labs
-20.00
-40.00
-40.00
-60.00
-60.00
-80.00
-80.00
-100.00
-100.00
-120.00
-120.00
-140.00
-140.00
0.00 Hz
4000.00
8000.00
12000.00
16000.00
0.00 Hz
20000.00
dBFS
0.00
Newport Test Labs
4000.00
8000.00
12000.00
16000.00
20000.00
Graph 4: Total harmonic distortion (THD) at 1kHz at rated output (70 watts) into a 4-ohm
non-inductive load, referenced to 0dB (Tetrode Mode). [VTL MB-125 Power Amplifier]
Graph 1: Total harmonic distortion (THD) at 1kHz at an output of 1-watt into an 8-ohm
non-inductive load, referenced to 0dB (Tetrode Mode). [VTL MB-125 Power Amplifier]
dBr
1.00
Newport Test Labs
0.80
-20.00
0.60
-40.00
0.40
0.20
-60.00
0.00
-80.00
-0.20
-0.40
-100.00
-0.60
-120.00
-0.80
-1.00
-140.00
0.00 Hz
4000.00
8000.00
12000.00
16000.00
20000.00
Graph 2: Total harmonic distortion (THD) at 1kHz at an output of 1-watt into a 4-ohm
non-inductive load, referenced to 0dB (Tetrode Mode). [VTL MB-125 Power Amplifier]
dBFS
0.00
Newport Test Labs
10.00 Hz
100.00
1000.00
10000.00
Graph 5: Frequency response of line input at an output of 1-watt into an 8-ohm noninductive load (black trace) and into a combination resistive/inductive/capacitive load
representative of a typical two-way loudspeaker system (red trace) (Tetrode Mode). [VTL]
dBFS
0.00
Newport Test Labs
-10.00
-20.00
-20.00
-30.00
-40.00
-40.00
-60.00
-50.00
-60.00
-80.00
-70.00
-80.00
-100.00
-90.00
-100.00
-120.00
-110.00
-140.00
-120.00
0.00 Hz
4000.00
8000.00
12000.00
16000.00
20000.00
Graph 3: Total harmonic distortion (THD) at 1kHz at rated output (55 watts) into an
8-ohm non-inductive load, referenced to 0dB (Tetrode Mode). [VTL MB-125 Amplifier]
0.00 Hz
6000.00
12000.00
18000.00
24000.00
30000.00
Graph 6: Intermodulation distortion (CCIF-IMD) at an output of 1-watt into an 8-ohm
non-inductive load, referenced to 0dB (Tetrode Mode). [VTL MB-125 Power Amplifier]
59
vtl mb-125 monobloc amplifiers
Lab Report
harmonic distortion components were
all below –60dB (0.1%), and above
5kHz, were mostly around 80dB down
(0.01%) or more. The small spikes
(‘grass’) around the fundamental (at
1kHz) and the harmonics indicates that
the VTL MB-125’s power supply was
working very hard during these (continuous) tests.
Intermodulation distortion (CCIFIMD) is shown in Graph 6, and you can
see that as with almost all valve amplifiers, there’s a considerable (–70dB)
signal regenerated down at 1kHz as a
result of the two test signals (at 19kHz
and 20kHz). There’s also a signal at
2kHz (–80dB). However these regenerated signals are still quite low in level
for a valve amplifier, so the VTL MB-125
appears to have less CCIF-IMD than
many competitive designs.
As alluded to previously, the unweighted signal-to noise ratios reflect
some noise in the power supply section
of the amplifier, with Newport Test
Labs measuring overall figures of 54dB
referred to an output of one-watt and
73dB referred to rated output. Applying standard IHF A-weighting to these
results, to simulate the level of noise
that would be perceived by the human
ear, you can see that the S/N figures
improve to 72dB and 90dB respectively.
These are good results for a valve amp.
The square wave tests (see the four oscillograms) present much of the data already
measured in abbreviated (but difficult to
read!) form (which is why square waves
are such a useful tool in amplifier analysis).
The VTL MB-125’s frequency extension is
obvious from the 100Hz and 10kHz square
waves, but the 100Hz wave also shows the
MB-125 has excellent low-frequency phase
accuracy. Particularly impressive is the amplifier’s ability to cope with highly capacitive
loads (2µF). The small overshoot visible on
all the square waves (including the one into
the capacitive load!) is due to that peak in
the amplifier’s response at 50kHz, mentioned previously which, however, because
of its frequency will be audibly benign.
Mains power consumption will be high,
with this single monobloc amplifier drawing
more than 100-watts from your mains at
all times, and peaking at pulling more than
250-watts if you sustain playback at high
volume levels.
Obviously in a system you’d have two
amplifiers operating, so you need to double
these figures to obtain ‘real’ consumption.
The lesson is to switch your pair of VTL MB125s off whenever you’re not using them.
(And using a dedicated 240V power outlet
might also be helpful).
Overall, the VTL MB-125 is a very welldesigned valve amplifier that delivers excellent performance for its genre.
Steve Holding
VTL MB-125 Power Amplifier - Power Output Test Results
Channel
Load (Ω)
20Hz
(watts)
20Hz
(dBW)
1kHz
(watts)
1kHz
(dBW)
20kHz
(watts)
20kHz
(dBW)
Tetrode
8Ω
76
18.8
82
19.1
61
17.8
Tetrode
4Ω
81
19.0
81
19.0
60
17.8
Triode
8Ω
38
15.7
36
15.5
20
13.0
Triode
4Ω
40
16.0
40
16.0
20
13.0
Note: Figures in the dBW column represent output level in decibels referred to one watt output.
VTL MB-125 Power Amplifier - Test Results
Test
Units/Comment
12Hz – 94kHz
–1dB
Frequency Response @ 1 watt o/p
7Hz – 110kHz
–3dB
THD+N
Signal-to-Noise (unwghted/wghted)
Signal-to-Noise (unwghted/wghted)
Input Sensitivity (CD Input)
Output Impedance
Damping Factor
Power Consumption
60
Measured Result
Frequency Response @ 1 watt o/p
0.18%
@ 1-watt
54dB / 72dB
dB referred to 1-watt output
73dB / 90dB
dB referred to rated output
90mV / 546mV
0.54Ω
14.8
NA / 112
(1-watt / rated output)
OC =
V
@1kHz
watts (Standby / On)
Power Consumption
115 / 251
watts at 1-watt / at rated output
Mains Voltage Variation during Test
240 – 252
Minimum – Maximum
Subscribe And
Save
On TEST
BeTTeR
THan
SonoS?
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November/December 2013
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January/February 2014
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Hear the sound…
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FATHER
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