Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site catnip.UUCP
Path: utzoo!decvax!bellcore!ulysses!mhuxr!mhuxn!ihnp4!houxm!hjuxa!catnip!ben
From: ben@catnip.UUCP (Bennett Broder)
Newsgroups: net.audio
Subject: Re: advice on CD players
Message-ID: <264@catnip.UUCP>
Date: Sun, 16-Mar-86 11:52:48 EST
Article-I.D.: catnip.264
Posted: Sun Mar 16 11:52:48 1986
Date-Received: Tue, 18-Mar-86 23:22:23 EST
References: <817@alberta.UUCP> <253@catnip.UUCP> <601@mmm.UUCP>
Distribution: na
Organization: The Broder Residence, Holmdel, NJ  07733
Lines: 56

In article <601@mmm.UUCP>, schley@mmm.UUCP (Steve Schley) writes:
> In article <253@catnip.UUCP> ben@catnip.UUCP (Bennett Broder) writes:
> >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 is a pretty strong statement, without any hard facts to back it up.
> It _is_ possible that three-beam pickups might die young.  See below.
> 
> >This salesman seems to suffer from the common
> >misconception that 3 beams means 3 lasers.  This just isn't the case.
> > {description of 3 beam technology}
> 
> This is, to the best of my knowledge, an accurate description of how
> three-beam pickups work.  Now, let's try a thought experiment,
> comparing the two types of pickups.  To get the same raw data S/N from
> the disc, I suggest that the intensity of the three-beam pickup's
> center beam must equal the total intensity of the single-beam pickup's
> laser.  Since the three-beam pickup is also generating two side beams,
> its total output must be greater than that of the single beam pickup,
> which means higher power dissipation in the diode.  This generally
> reduces life expectancy of an electronic component.
> 

Single beam lasers have a much wider beam. Tracking information
must still be provided for the servo circuit.

> I do not know of any studies that discuss actual failure rates of CD
> player laser diodes.

Neither do I, though the one case I know of where a laser diode failed
was an old top loading Magnavox, a single beam design.

> >This mechanism gives a three beam player a big advantage in
> >tracking eccentric discs.
> 
> This statement, while possibly true in specific comparisons, is not
> true in the general case.  A while back, reviewers were finding that
> certain Philips single-beam players would out-track certain Japanese
> three-beam players on defective discs.

By eccentric discs, I mean those with the hole punched off-center, not
with other types of defects.  According to the service technician I spoke
with at Studer/Revox (a company that makes single beam units), the
configuration of the three beam machines is much more resistant to this
type of mistracking.

-- 

Ben Broder
{ihnp4,decvax} !hjuxa!catnip!ben
{houxm,topaz}/