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From: michaelk@tekmdp.UUCP
Newsgroups: net.audio
Subject: Re: linear tracking turntable inquiry
Message-ID: <1998@tekmdp.UUCP>
Date: Thu, 2-Jun-83 14:30:15 EDT
Article-I.D.: tekmdp.1998
Posted: Thu Jun  2 14:30:15 1983
Date-Received: Wed, 8-Jun-83 22:46:43 EDT
References: tesla.85
Lines: 37

Yes the Sony PSX-800 "learning" is not turned off after the first few
tracks, it is continuously learning, and correcting , it is just the first
few track revolutions that some error is guaranteed.  The point I was
trying to make is that unlike "dumb" tonearms that are ONLY drug across the
face of the record, or linear trackers that do a sawtooth correction (a simple
correction loop that has a tracking angle sensor, and just "corrects" the
position whenever the sensor trips, thereby giving a sawtooth error), the
SONY does try to establish a horizontal movement, that given a record with
evenly spaced grooves, would sit dead center in the groove, with zero
tracking angle error for the entire record.  Now then, this learning
mechanism in addition to the linear tracking construction results in the
first order errors corrected. The error correction closed loop (with
the tracking angle sensor, etc) becomes a second order effect corrector, rather
than first order corrector. I might point out that all words "error" above
refer to very small numbers on an absolute scale, and refer generally to
relative error in a linear tracking environment.
    While I am at it, I might explain the SONY biotracer construction.  The
linear tonearm has (obviously) freedom of movement on a grand scale
horizontally when the whole arm moves.  The arm also has a large vertical
movement freedom (up and down) that is obvious. But, it also has a limited
horizontal movement a little either side of perpendicular to the carriage.
In the arm (near the pivot point) are vertical and horizontal oriented
velocity sensors, and linear motors.  It uses these to actively null out
arm resonances, and gives the arm a measurable, effective mass of zero.
Some of the interesting side benefits are that it automatically balances
the arm everytime it picks it up.  So if you change the cartridge (that
universal mount) to a different weight one, instant re-balance.  Additionally,
it uses a bias on its vertical linear motor to generate the vertical tracking
force.  This makes the tracking force knob a potentiometer off to the side,
and you can turn it while playing the turntable to see how the cartridge
tracking is doing "real-time".  Likewise, it provides a more consistant vertical
force on warps.  The innards of the thing is PC board galore.  Scratches
on the records still go pop though.

Mike Kersenbrock
Tektronix Microcomputer Development Products
Aloha, Oregon