Fixed Pickup Mechanism - Sony SCD-1 Technical Background

2.2. Fixed Pickup Mechanism.

Optical playback systems require motor servos,
tracking servos and focus servos to maintain
accurate playback. Unfortunately, the laser out-
put is extremely low in level—making it extremely
sensitive to radiated noise. That includes noise
induced from the servo currents!
While servo currents obviously can't be
eliminated, they can be isolated, controlled and
reduced by Sony's Fixed Pickup Mechanism. It
creates a quiet environment for clear, low-noise
signal readout.
Typical laser transports mimic the design of LP
turntables. The spindle, disc and motor are fixed
in position. The laser acts like a phono cartridge,
tracking across the radius of the disc. The Fixed
Pickup Mechanism changes everything. To iso-
late servo voltages from the laser pickups, the
pickups themselves are fixed, rigidly bolted onto
a subchassis. While the pickups remain station-
ary, the disc and turntable move horizontally to
accomplish tracking. As a result, the system
achieves extremely precise tracking—with
extremely low induced servo current noise.
Sony's Fixed Pickup Mechanism
suppresses servo-induced noise.
This Fixed Pickup design—first used in Sony's
critically-acclaimed CDP-XA7ES Compact Disc
player—has been further refined by highly
advanced sub-assemblies:
• Spindle motor. Made of die-cast aluminum for
high rigidity. The stator (stationary side)
includes a sapphire bearing. The rotor (rotating
side) features a ruby ball that fits into the
sapphire bearing. This combination makes for
incredibly smooth rotation — and reduced
motor servo current. It also reduces wear at
the contact point.
• Base plate. The drive mechanism is mounted
to a solid aluminum plate, 6 mm (1/4 inch)
thick. The spindle cutout is reinforced with an
extra plate for added rigidity. Special openings
suppress vibration, to reduce servo currents
further still.
• Floating suspension. The entire mechanical
block floats on four rubber dampers, mounted
on four chassis pillars. The design combines
high rigidity with superb isolation from chassis-
borne vibration.
• Disc stabilizer. The disc is held onto the spin-
dle by a massive brass stabilizer that the
user places over the center hub. This dampens
extraneous motion and helps create a
high-precision rotating system.
The die-cast aluminum spindle motor is highly rigid.
A unique ruby rotor ball bearing minimizes
friction and servo current.
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