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Nº32
REFERENCE PREAMPLIFIER
The Nº32 Preamplifier is a revolutionary Mark
Levinson component. It is the first preamplifier to
earn the Reference label.
Separating power-supply and control circuit-
ry makes sense in a modern, Reference-level
preamplifier. AC power supplies, microprocessors,
LED displays - essentially, anything that gener-
ates noise - are housed in a separate chassis from
the low-level audio signals (the Nº32 Reference
Controller), while all of the audio-preamplifier
circuitry is housed outboard (the Nº32 Reference
Preamplifier). Thus, the audio circuits are exposed
only to quiet, regulated DC power and the audio
signal itself.
Two master power supplies are located in
the center section of the Reference Controller:
one is dedicated to control and communications;
the other is used for the audio circuits. The power
from the AC line is pre-filtered, and the two
master supplies are isolated from one another. The
power supplies use custom-designed transformers
featuring multiple secondary windings, which
substantially improve isolation between separate
circuit blocks. Separate rectification, filtering, and
regulation circuits are used to supply DC to the
control/communications circuits, a Nº25 phono
DC supply output, and the 400Hz oscillator
circuits used in power-supply regeneration.The Nº32 employs AC power regeneration:
the DC supply feeding the voltage gain stages is
derived from an AC source generated within the
amplifier itself. This technique is expensive but
very effective. In the Nº32 Reference Controller, a
400Hz oscillator generates the AC source for the
preamplifiers audio power.
Microprocessors are noisy devices which
can pollute low-level audio signals if care is not
taken to keep processing noise out of the signal
path. For this reason, the microprocessors in the
Nº32 are not only located in the controller box,
physically separated from the preamplifier chassis,
but are also within their own shielded box.
The microprocessors in the Nº32 control
volume changes, signal routing, and other switch-
ing functions. They make it easy to name inputs,
select mono modes, set mute level, or program
offset or gain levels for individual inputs - all
from the front panel. Like other current Mark
Levinson components, the Nº32 uses a software-
based operating system that can be upgraded
through its RS-232 port.
The Reference Preamplifier chassis has no
buttons or knobs. The Reference Controller is
used to execute all commands through its simple
front panel. Each source can be named in the
display, and full control of all functions, with the
addition of mono/stereo selection and polarity
control, is available from the remote.
The Nº32s casework is extraordinary even
by Mark Levinson standards, and, like the other
aspects of its design, reflects an uncompromising
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approach. Its chassis is a custom aluminum
casting, machined and finished with a conductive
Irridite (clear chromate) coating. This design
approach assures a rigid, stable environment in
which vibration and microphonic effects are
controlled.
The left and right channels are separated by
a solid aluminum divider wall, formed as part of
the casting. Each channel is thus sealed into its
own environment to prevent the electromagnetic
noise of one channel from degrading the other.
Because each channel is effectively isolated from
the other electrically and physically, the Nº32s
stereo separation is equivalent to that of two sepa-
rate mono preamplifiers.
The Nº32 is the first Mark Levinson product
to use Arlon 25N
®for its circuit boards. This
materials superb dielectric properties help the
Nº32 achieve remarkable performance with
complex audio signals. Arlon 25N was chosenonly after extensive listening tests revealed that it
was audibly superior to all other materials in this
particular application.
Both balanced and single-ended inputs are
provided on the rear panel. Single-ended signals
have common-mode noise (noise present on both
signal and ground) rejected at the input stage.
Fully balanced instrumentation amplifiers are
employed as the gain stages, and each input can
be separately adjusted using the software to offer
0, 6, 12 or 18dB of gain. Using this feature, the
Nº32 allows the volume control to work in its
optimum range even when its sources have
substantially different output levels.
While volume control is one of the primary
functions of a preamplifier, it is also a source of
compromise in many designs. The Nº32
introduces a new active attenuator: a discrete
design that offers an unprecedented combination
of precision and neutral sonic performance. The
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