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From: ben@catnip.UUCP (Bennett Broder)
Newsgroups: net.audio
Subject: Re: advice on CD players
Message-ID: <253@catnip.UUCP>
Date: Mon, 3-Mar-86 23:15:16 EST
Article-I.D.: catnip.253
Posted: Mon Mar  3 23:15:16 1986
Date-Received: Thu, 6-Mar-86 02:50:32 EST
References: <817@alberta.UUCP>
Distribution: na
Organization: The Broder Residence, Holmdel, NJ  07733
Lines: 26

In article <817@alberta.UUCP>, luca@alberta.UUCP (Luca Vanzella) writes:
> One thing in particular - a local dealer (carries JVC, Sanyo, and Sony) 
> suggested to me that 3-beam laser units would not last as long as 1-beam
> laser units due to "the power configuration".  He suggested 6-8 years
> life expectancy vs 8-10 years.

This is just not true.  This salesman seems to suffer from the common
misconception that 3 beams means 3 lasers.  This just isn't the case.
The three beam units use half silvered mirrors to split the beam of a
single laser into three individual beams.  The center beam is used for
reading audio information -- it is equivilent to the single beam used
in other machines.  The other two beams are aimed just to the left and
right of the track.  The outputs from the photodetectors from the side
beams are compared.  If the unit is tracking properly, the difference
should be zero.  But if the pickup is off slightly, one of the auxiliary
beams will be dimmer (because it will be catching the edge of the pits).
The sign and magnitude of the difference between the two auxiliary beams
tells the player how much of a correction it needs to make and in what
direction.  This mechanism gives a three beam player a big advantage in
tracking eccentric discs.

-- 

Ben Broder
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