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AGC range

post #1 of 9
Thread Starter 

What is the Agc. range? I was reading a thread on audiokarma about why older CDp's and even some newer ones will not play burned CD's and someone said that the AGC range is often not enough for the player to read the CD.

post #2 of 9
Quote:
Originally Posted by RaymondLeggs View Post

What is the Agc. range? I was reading a thread on audiokarma about why older CDp's and even some newer ones will not play burned CD's and someone said that the AGC range is often not enough for the player to read the CD.

When a CD player reads a disc, it fires a laser into it and looks for reflected light modulated by the pits in the reflective layer.  Normal manufactured CDs have fairly well controlled reflectance, but there is still a variation in the amount of light reflected back, which affects the ability of the player to read the pit pattern without errors.  So, when a disc isn't as reflective, the player cranks up the laser power and/or the gain of the reader to compensate.  If it's highly reflective, they back things down.  The action is generally called AGC for Automatic Gain Control, though I think that's not exactly the right term for this application.  In repair manuals its not aways called AGC, but the function is the same.

 

A recordable disc may have a much wider range of reflectance, usually lower than a normal CD, and that's part of why some players have trouble with recorded discs.  A players AGC range is the range of automatic adjustment that can compensate for disc reflectance variation.  If a disc is just not reflecting enough light, and the AGC is all the way up, the read errors will be huge and the player may either not read it at all, or be very erratic.  

 

CD burners usually have highly capable readers, so it's practical to copy the problematic disc to a better blank and solve the issue.  

 

Players also age, and laser power does decrease over time.  Older players may not have the ability to read a CDR anymore because of lasers aging out. There used to be adjustments to compensate for this, it should all be automatic now, right up until laser failure.  

post #3 of 9
Thread Starter 

My Denon Player doesent play burned CD's 

post #4 of 9

Older CD players might have more compatibility issues. What Denon model do you have?  If it's supposed to read CDRs and or CDRWs you might want to consider replacing the pick-up head (repairs.)

 

Like Jaddie said, lasers are age and temperature dependent.

post #5 of 9
Thread Starter 

Its an Old Denon DCM-50 From 1996 Most burned Cd's I have are not that great anyway. It works well with normal Cd's though. In fact it plays them Better than the newer Sony disc player does.  Both Sonically and physically. 

post #6 of 9

Playing CD-Rs reliably didn't become a common feature in home CD players until the late 1990s, early 2000s, coinciding with cheap CD-R blanks, and the download boom.  It's not common to find a player from the mid 1990s and earlier that could handle them well.  

 

It may not be a repair issue, especially since the cost of repair of a 17 year old player would exceed its value, unless it was a very special high-end player. 

 

You might try copying those old CD-Rs to new blanks.  The newer ones have somewhat higher reflectivity, and the process would be cheap and fast.  Even better would be a rip/burn using error correction.  I'll bet you get some playing after that, especially if your CD-Rs are on old media.

post #7 of 9

If you are happy with it, definitively keep it. I did a cursory check and the pick up heads for the player seem to go for > $50. But then again, maybe nothing is wrong with it and the player just doesn't support CD-Rs.


Edited by ultrabike - 3/11/13 at 6:15pm
post #8 of 9
Thread Starter 

It is a second hand CDp anyway, and the CDR's are not that old. the oldest is from 2008. 

 

I opened it up once and it was flithy! .

post #9 of 9
Quote:
Originally Posted by RaymondLeggs View Post

It is a second hand CDp anyway, and the CDR's are not that old. the oldest is from 2008. 

I opened it up once and it was flithy! .
If you get a minute, open it up again and see if you could clean off the lens on the laser assembly. Be gentle and use something soft. Dirt on a lens does reduce its ability to read a marginal disc.
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