How the Laser Turntable Works

Scanner mirrors

Two tracking laser beams are directed to the left and to the right shoulders of the groove of the record. Only the part of the beams that reach the groove are reflected to two PSD (Position Sensitive Detector) optical semiconductors. The part of the beams that fall on the land area of the record are deflected and not picked up by the PSD devices. The signals are sent to a microprocessor via analog to digital converters, then to servos to maintain the reader head position directly above the groove.

The laser tracking beam

Two additional laser beams are directed at the left groove wall and the right groove wall just below the tracking beams. Modulation on the individual grooves is reflected to scanner mirrors and onto left and right photo optical sensors. The variations of the modulated light cause the audio sensors to develop an electrical representation of the mechanical modulation of the grooves. The entire sound reproduction chain is analog.

The distance from the surface of the record to the traveling pickup head is kept constant by using a separate laser beam. This is very similar to every CD player that uses a "focus" laser to move the laser that reads digital bits to the proper spacing between the reader and the disc. Since phono records vary in thickness, this feature assures precision alignment from the pickup head to the record. The servos are fast and responsive allowing the LT to accommodate even warped records. Also the new audiophile 180 gram (thick) records are reproduced beautifully.

Interior view of the Laser Pickup Head

A view of the inside of the Laser Pickup Head.

A special calibration LP record is provided with each Laser Turntable and is used to set up the optics and microprocessor. The record has about 20 minutes of grooves with no sound. It is necessary to run this special disk for about 30 seconds.

The calibration disk should be used when you operate the machine for the first time. Every few months you may elect to run the calibration disk to maintain tracking accuracy, particularly if you notice any mis-tracking during playback. When the machine is moved to another location, it is wise to run the calibration disk again.

The Laser Turntable is, no doubt, the most sophisticated and state-of-the-art "record player" ever designed.

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Reported by
Sanju Chiba,President & CEO
ELP Corporation, Japan
Conatct: chiba@elpj.jp

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