Please read my post again.
I said that AGC is a threshold detector function. It has nothing to do with
laser diode power calibration.
Sony players do nothing special with the laser diode. The AGC function
provides variable threshold detection, which is what gives it the ability to
read Orange Book.
"Mark D. Zacharias" wrote in message
...
And yet the laser power is not calibrated according to any disc
reflectivity, merely to provide a constant laser current, which is
virtually
the same regardless of whether any laser light returns from the disc at
all.
In a multi-read model, which I will admit I have not studied, this may be
different. Your old Sony however, isn't multi-read in the same sense as a
modern CD-ROM device. It may just have the laser power turned up somewhat.
The only unit I have seen which calibrated the laser output on playback
was
a karaoke model - unknown Chinese vendor. Viewing the HF pattern on a
'scope
one could observe the laser "eye pattern" ramping up depending on the disc
type. Your Sony does not do this.
Mark Z.
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"Robert Morein" wrote in message
...
"Mark D. Zacharias" wrote in message
...
I was talking CD-R, not RW, haven't tried those in the older Sony's
but
I
would be surprised. Lots of other units use the Sony pickups, and none
of
them boost the laser power based on reflectivity - a constant current
is
maintained as a voltage drop across a resistor, indicating a constant
laser
diode current, regardless of reflected signal received back to the
diode
pack. The APC (not ACG) transistor is mainly a switch, though as I say
the
current is kept nearly constant.
Mark Z.
I did not intend to imply that AGC is an adjustment of the laser diode.
It is an adjustment of the threshold detector.
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"Robert Morein" wrote in message
...
Sorry, Mark, I can't agree.
The following tech sheet
http://www.sanyo.com/semiconductors/news/Vol66.pdf
gives specs on the Sayn LA9251M, a common CD controller chip.
Among the features provided is
. Automatic follower operation (tracking gain and track detection
level)
Because lasers wear and output decays over time, calibration to the
reflected signal at a particular point in the life in the product is
essential.
This feature is frequently referred to as AGC, and has been
implemented
with
varying degrees of effectivenss in different players.
For example, every Sony player I own, back to 1991, is multi-read
capable,
which means that it can read a CD-RW, which of all the available
blanks
differs the greatest from a pressing.
Most other brands were, at least in the past, not nearly so good. It
is
remarkable that Sony built multi-read into their products long
before
CD-RW
was in frequent use.
I have the service manual for all my players, and none of these
older,
multiread capable units have either a calibration pot or a service
mode.
"Mark D. Zacharias" wrote in message
...
With VERY few exceptions, audio CD players do not calibrate laser
power
automatically. Some are adjusted with physical potentiometers,
some
newer
ones do it in a service mode using eeproms, but once set, the
laser
calibration is done.
Focus is adjusted dynamically while playing, and of course during
the
focus
search routine. Focus offset value is kept in memory until the
next
disc
read operation so that if the PLAY button is pressed again, it can
spin
immediately without doing another focus search.
Mark Z.
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"Robert Morein" wrote in message
...
"Surinder Singh" wrote in message
...
I play the CD's I burn in Phillipps Boombox. If I Maxell Gold
CD-R
it
takes
20 seconds for the boom box to recognize the tracks and be
ready
to
play
it
after inserting the CD. With Memorex 52x, it takes only 2
seconds
for
boom
to recognize the tracks. Does it mean that Memorex is better
quality?
I
would have thought the gold coloration ;-) & Maxell name would
make
the
former a better quality?
Thanks.
Different CD disks have different reflectivities for the burn/no
burn
conditions.
The CD player has a calibration function that enables it to
correctly
recognize these conditions.
Depending upon the design of the player, the ability to
recognize
disks
with
different reflectivities vary.
Only a few years ago, it was common for many brands of CD
players
to
fail
to
recognize CD-Rs, because insufficient range had been built into
the
calibration function.
What you observe has more to do with the player than the disk.
Gold as a reflective material has a signficant advantage for
archival
use.
However, it is somewhat less reflective than aluminum.