Concept 2qd brochure

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@©[N]@EPT

The Ultimate in _
Sound Reproductlon

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Concept

Concept ZQD-the result of a
concerted effort to design a turntable
that offers both ultimate precision and
ultimate convenience. Every detail. from
the action of the controls to the damping
material of the feet. has been carefully
thought out and crafted by a distin-
gUished international team of deSigners
and production engineers. The final
result is a remarkable record playing
instrument-a turntable to satisfy even
the most discerning audiophile.

Experience the calm authority of the
Concept 20D. Look at it. operate it.
hear your favorite records played on it.
You'll find the Concept 20D offers more
than the best competing models

Two Critical Factors

As we completed the development of
our laboratory standard electronics and
constant energy speaker systems, we
began critical listening to a wide variety
of the most dynamic recorded material
availableiincluding the highly modula-
ted direcHo-diso and digitally recorded
pressings. We became acutely aware of
two problems that plagued many
turntables. inadequate speed stability
and excessive tonearm inertia.

We set out to design a turntable that
would maintain highly accurate, highly
stable speed-even when subjected to
the increased drag caused by a stylus
tracking highly modulated grooves of
the loudest passages. And we set out to
develop a tonearm that would minimize
mistracking due to uncontrolled reso-
nance and excess inertiaemistracking
that limits dynamic range, drains amplifi-
er power. and that leads to audible
distortion on the loudest passages.

We wanted a record playing system
to reproduce the most lively recordings
without any audible loss in the full
dynamic range and sonic integrity of the
music. With the development of the
20D, we feel we have succeeded.

Quartz Control Improves
Direct-Drive Speed Stability

Constant platter speed must be main-
tained continuously or there will be
noticeable distortion (wow and flutter) in
the sound of mu5ic. While many turns
table drive systems are designed to
maintain consistent rotational speed
under low-stress or non-stress condi-
tions, the increased friction that comes
from a stylus tracking a highly modula-
ted groove will cause minute fluctuations
in the speed of these drive systems,

Recognizing this fact, Concept engineers
set out to develop a drive system that
would maintain constant speed under
varying load conditions.

The direct drive system has proven
capable of maintaining the most consis-
tent speed control yet achieved in stan-
dard turntable design. By mounting a
massive platter on top of a low-speed.
high torque motor. a direct- coupled fly-
wheel is produced This technique over~
comes many factors that tend to
degrade the speed stability of other
designs.

To absolutely eliminate speed fluctua-
tion problems, however. a motor control
system was needed. This system would
keep the motor precisely regulated so
that minute speed fluctuations were
detected as they happened and
corrected immediately.

The quartz crystal is one of natures
most accurate time references. Crystal
references are used for the precise
control of instruments ranging from
standard-maintaining chronometers to
radio transmitters When stimulated by
an electrical current. the crystal will
vibrate at an extremely stable frequency.
By using crystal control in the drive
circuit of the Concept 20D, it is possible
to achieve a laboratory standard of
speed control.

The 2ODs DC drive motor is
equipped with a builtain frequency
generator. While the motor/platter
system is rotating at a constant speed.
the output of this generator is a constant
frequency. Any deviation in the speed of
the motor/platter system is detectable as
a change in this frequency.

A phase-locked-loop (PLL) system
compares the output of the motors
frequency generator with the precisely
controlled frequency of the quartz
crystal oscillator. The most minute
speed changes initiate a correcting
voltage from the PLL which adjusts the
motors driving circuitry and instantane-

Ouarthlocked PLL servo system

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ously corrects the speed variation. This
sophisticated control circuit, consisting
of 4 integrated circuits plus associated
discrete parts. assures that increased
dragias when the stylus tracks highly
dynamic material or when a tracking
record cleaner is being usediwill not
cause platter speed variations,

The DC servo platter drive motor
used in this quartz-locked system has
been engineered ,with a high stall torque
of GEOcm/g. High torque gives the motor
a margin of power for maintaining cor-
rect speed even under extreme load
conditions. And due to this high torque,
the platter drive system reaches full
speed quickly-in a maximum of 1.8
seconds.

The 90-pole armature frees this motor
from another speed variation problem:
cogging. Cogging is a minute starting/
stopping that can be heard as wow and
flutter in turntables with fewer poles. The
motor has been further refined with the
elimination of friction»inducing brushes.

The platter sitting on this high torque
motor is 3V2 lbs. (1.7 Kg) of die cast
aluminum, precision machined to
achieve the most delicate balance possi-
ble.This massive platter serves as a fly-
wheel 1or the drive system, further redu-
cing the problems of a speed variation.

The machined strobe markings on the
platter are illuminated by a 3-LED
strobe. This strobe is driven by circuitry
referenced to the highly accurate crystal
oscillator so that it is immune to fluctua-

The quartz crystaiibne ol natures most
accurate time references