Kenwood L-07D Instruction Manual page 3

was formerly driven at constant voltage. In the
L-07D, however, the motor coil is driven at cons-
tant current, therefore, counter electromotive
force in the coil can be ignored and control can
be more precise.
The L-O7D uses double servo coupling which
automatically switches the control method when
the speed differs by + 3%, from the rated speed:
when the speed difference is beyond + 3%, the
speed is controlled to obtain a large torque and,
when it is less than + 3%, the phase is controll-
ed to obtain a wide lock range and large phase
gain,
Further, at a speed of +3%, the circuit
coupling is changed from DC to AC to reduce in-
fluences from the motor drive circuit and the
motor offset.
if the moment of inertia varies to a great ex-
tent (e.g. if KENWOQD''s disc stabilizer DS-
20/DS-21 are used), the dynamic parameter
(time constant) can be changed
Anti-vibration, complex structure turntable plat-
ter with high transient load characteristics and
large moment of inertia
A moment of inertia of 1.025 kg:cm? is ob-
tained (when the turntable sheet is attached),
resulting in high kinetic energy of rotation.
Therefore, the platter rotates stably even if the
transient load from the stylus varies. The
mechanical impedance supporting the record is
kept high, so that signals cut in the record can be
traced exactly by the stylus
The turntable platter is made of diecast
aluminum inside of which there is Duralumin
4mm thick, The top surface of the platter is
finished accurately.
Further, a nonmagnetic stainless steel turn-
table sheet is mounted on the platter so that
good anti-vibration properties are obtained
Non-resonant boron laminated pipe tonearm
with high stiffness
Light and rigid materials must be used for the
tonearm to raise the resonant frequency of the
tonearm. In the L-O7D, super-hard aluminum as
used in air frames together with carbon and
boron fibers are used for the tonearm. This
3-layer structured tonearm has high stiffness
and, because of the combination of different
materials resonance is suppressed and_in-
fluences degrading stylus performance are
eliminated
The head shell attached is a 7-layer carbon-
boron laminated structure, therefore it is light as
well as extremely stiff.
Highly accurate and rigid pickup loop
The pickup loop, which is the signal conver-
tion system of the turntable and picks up the
signal cut in the record, includes "3 fulcura'' —
the platter support point (center shaft), the
tonearm support point (pivot) and the cantilever
supporting point —, these are most important in
any turntable system. The accuracy of the posi-
tions of these ''3 fulcura'' is generally accepted
as determining the performance of the turntable.
The most important requirement of ''ideal con-
version' is that the locations of these ''3
fulcura'' relative to the groove of the record do
not change
In the L-O7D, 12mm (15/32'') diameter
hard stainless steel is used for the precision
finished center shaft so that performance is im-
proved. To support the heavy turntable platter, a
floating magnet is used, so that viscous
resistance of the thrust pad, etc is reduced and
the cutoff frequency of the motor is lowered
Carbon tool steel is used for the tonearm
pivot and stainless steel is used for the rotating
shaft together with over-sized bearings.
Therefore, the tonearm turns smoothly around
the supportilng point and all other motions are
eliminated. The cantilever supporting point must
be 100% stationary. If not, unnecessary signals
wil be picked up or the music signal will be
modulated, resulting in degraded sound.
Collet chuck type, highly-rigid tonearm base
The tonearm shaft is fixed by means of a col-
let chuck to the tonearm base which is made of
brass and stainless steel. The tonearm base is
equipped with the helicoid height adjustment
mechanism which enables highly accurate
height adjustment at a rate of 0.1 mm per turn
for a total height of 7 mm. The tonearm shaft is
also made of BSBM material and has a diameter
of 27.6 mm (1-3/32"').
Whatever the force from the collet chuck the
tonearm shaft is never deformed. The tonearm
base and tonearm shaft weigh a total of 3 kg.
This mass-concentration design improves
strength and resistance to external mechanical
interference.
L-o701K) 3