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N
53
REFERENCE POWER AMPLIFIER
B
L
ORN OF
ISTENING
New Mark Levinson products are not introduced with
the seasons, or according to arbitrary marketing
schedules. They're introduced as new technologies,
which have shown promise on paper, are perfected and
proven through rigorous in-house development and
o
evaluation procedures. In the case of the N
53, a highly
experienced evaluation team was assembled to conduct
blind and sighted listening tests of a novel switching
amplifier prototype, measuring it against past and
present Mark Levinson linear power amplifiers as
well as a range of competitive products.
As the development process wore on, power amplifiers
deemed sonically inferior were removed from further
testing. Several judges were surprised to learn that the
new switching amplifier was never among them. In
o
fact, the early N
53 prototype emerged as a winner,
with several panelists awarding it top honors for speed,
dynamics and clarity. It was, to say the least, an
unexpected result. For a mere prototype switching
amplifier to hold its own against linear amplifiers that
were deemed to be the very best the marketplace had to
offer – time-honored Mark Levinson models included –
meant we knew we were dealing with a
paradigm-shifting design.
Convinced that the minor quibbles that had come up
during the initial listening tests could be overcome, the
o
N
53 project was commissioned, and development of
the first new Mark Levinson Reference power amplifier
in more than a decade began in earnest.
T
T
C
HE
ECHNICAL
HALLENGES
All power amplifier designs have inherent pros and cons
based on their design topology, and switching designs
are no exception. On the plus side, switching amplifiers
are more powerful, smaller and run cooler than their
linear counterparts – by several orders of magnitude. As
o
points of comparison, the Mark Levinson N
33 is rated
at 300 watts into 8 ohms, measures 31 x 14 x 31 inches
o
and weighs in at 435 pounds, while the N
53 – at 500
watts, 21 x 9 x 21 inches and 135 pounds – is nearly
twice as powerful, substantially more compact and 300
pounds lighter.
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The N
53 is capable of generating truly phenomenal
power levels to support both the instantaneous and
continuous demands of virtually any speaker load. More
o
impressive, the N
53 accomplishes this feat while main-
taining a constant, thermally balanced operating temper-
ature. Although always warm to the touch, the operat-
o
ing temperature of the N
53 will not vary – or exhibit
even the slightest change in performance capability –
regardless of how long or hard the amplifier is driven.
The downside of switching power amplifiers? Because
they switch output devices on and off in very rapid
succession to mimic the input signal – one set of output
devices drives the positive half of the waveform, and a
separate set drives the negative half – switching noise
and dead bands become significant design challenges.
S
O
S
N
WITCHING
FF
WITCHING
OISE
In most switching power amplifier designs, a brick-wall
filter is placed above the audio band to remove switch-
ing noise. But because of the filter's physical proximity
to the audio band, this has a significant adverse effect
on phase relationships, the smoothness of frequency
response and imaging. In short, it degrades overall
sound quality. To overcome this challenge,
Mark Levinson engineers devised Interleaved Power
Technology (IPT), a patented method of raising the
o
amplifier's switching frequency. In the case of the N
53,
the switching frequency is raised to an extremely high
2MHz, delivering two major sonic advantages. First, it
pushes the fundamental switching noise and associated
harmonics so far above the limit of human hearing that
they have no direct effect on sound quality. (In fact,
most audio testing devices can't even measure such
frequencies.) Second, it allows for easier removal of
switching noise from the signal with much gentler notch
filters, which have no negative effect on the crucial
audio band. The result is frequency response that is
ruler-flat across the entire audio spectrum, dipping only
a few dB at 100kHz. That's impressive performance for
any power amplifier. For a switching power amplifier, it's
nothing short of remarkable.
E
D
B
LIMINATING
EAD
ANDS
The other technical challenge for switching power
amplifiers are dead bands – silent gaps in audio output
created when the output devices driving the positive
half of the signal and outputs driving the negative half
are both turned off. This occurs every time the audio
waveform crosses from positive amplitude to negative
amplitude, or back again (about forty thousand times per
second for a 20kHz audio signal). Because even the best
output devices cannot switch on and off instantaneously,
a signal gap is created between each half of every wave-
form. Large gaps are highly detrimental to the audio
signal, but even the tiniest gaps have a negative impact
on sound quality – listeners will perceive that something
isn't right.
Dead bands can be minimized by keeping both sets of
outputs off for as short a time as technically possible.
But doing that increases the possibility that opposing
output devices may come on at the same time –
doubling the voltage they draw – which could easily
damage or destroy them. Engineers are forced to arrive
at a middle ground between sound quality and reliability
when designing switching power amplifiers.
Mark Levinson engineers saw this as unacceptable and
o
instead developed a patented technology for the N
53
that permits both sets of output devices to be on
simultaneously for short periods of time. Dead bands
are completely eliminated, without in any way
compromising the life expectancy of the output devices.
O
L
PTIMIZING THE
AYOUT
The primary function of any Mark Levinson
Reference product is to reproduce sound at the purest
level possible. With power amplifiers, the challenge
is to amplify the incoming audio signal without
distorting it and to effortlessly drive a wide range of
loudspeaker impedances at any volume level with the
forcefulness and grace that Reference-quality sound
reproduction demands.
o
Toward that end, the N
53 chassis is a compact vertical
design with four separate internal compartments to
shield and isolate different kinds of circuitry. The power
supply – an extremely low-noise toroidal transformer
with an oversized 2.8kVA transformer and four
47,000µF low-ESR capacitors – is placed in the bottom
compartment to reduce interference from magnetic
fields and high-current devices. The two middle sections
contain four amplifier modules, which are arranged sym-
metrically and mirror-imaged to maximize separation.
The top compartment includes the control circuitry,
which has an independent regulated power supply that's
shielded from the rest of the amplifier to prevent audio-
circuit interference.
Eight large coils – two per amplifier module – essentially
create four separate power amplifiers, which are respon-
sible for the exceptionally high power levels, large
o
dynamic and stunning clarity of the N
53. Working
together, these amplifiers raise the effective switching
frequency from 500kHz to 2MHz, producing the best
sound quality ever achieved in a switching amplifier.
Special attention was paid to the signals that pass
between different boards. Extensive use of low-voltage-
differential signaling (LVDS) for control signals maxi-
mizes their integrity, while all analog signals remain
balanced for superb noise rejection.
I
'
Y
T
L
T
S
OUR
URN TO
ISTEN
With the technical hurdles of switching power amplifiers
behind us and with the internal layout finalized, the
o
N
53 development team headed back to the listening
room. We listened with different types of music. We
listened with different speakers, electronics and cables.
o
We listened in different rooms. We compared the N
53
to other Mark Levinson power amplifiers. We compared
it to the power amplifiers of our competitors. We
listened blind, we listened sighted and we flew in
customers from around the world to listen with us.
Only then, when we were convinced that we had
coaxed the last ounce of performance from this
o
revolutionary design, did the N
53 go into production.
Now we invite you to listen to the world's new
Reference standard, and experience the incredible depth
and detail it uncovers in any source material.
The modulator board is the "brain" of the system. It is located at the top of the
amplifier in order to provide shielding from the main amplifier section.
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