CD Transport Rumble

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Does anyone know what might cause an audio CD transport mechanism to to  
issue a rumbling noise when playing a commercial CD?  I've got beaucoup  
commercial CDs (mostly classical) in my collection and I've noticed this  
only on one CD (in this case a Philips label), even though it otherwise  
plays OK in the CD player.  That CD doesn't appear to be warped or  
abnormal upon visual inspection.  Thanks for your time and comment.  
J. B. Wood                e-mail: arl

Re: CD Transport Rumble
On Mon, 15 May 2017 11:39:24 -0400, "J.B. Wood"

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Off balance CD.  I've had it happen when someone attached a stick-on
label to a CD.  At high RPM's, the CD will vibrate.  I've also seen a
damaged hole in the CD cause the drive clamping mechanism to lock at
an odd angle, also causing vibration.  If it's only one CD, try to
make a copy of the CD.  If there is something wrong with the CD, the
copy should play normally.

Jeff Liebermann
150 Felker St #D
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Re: CD Transport Rumble
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I've seen a few CDs where the center hole wasn't "to spec".  It was
either slightly undersize, or had bits of plastic "burr" on the edges
of the hole.  As a result it would not drop down on the drive spindle
properly, and the CD would sit at a bit of a slant and would wobble
when spinning.

Going around the inside of the center hole with a small piece of
fine-grit sandpaper, to break off any burrs from the molding/stamping
process, and then cleaning the CD carefully to remove any sanding dust
and grit (rinse under running water) has usually worked out.  In cases
where it doesn't, I'd "rip" the CD and burn an exact copy, store the
original and use the copy as a play disc.

Re: CD Transport Rumble
J.B. Wood wrote:

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I had a CD player that started to do something like this.  Passages with  
only high notes came through well, passages with low notes just dissolved  
into something that could be called a rumble.  It was odd, the beginning of  
the CD played perfectly, at the end the audio was totally inaudible.  It was  
not a time thing, you could skip to the end of the CD and it would  
immediately be bad, skip to the beginning and it was fine.

After some poking I discovered the (brush) motor was shot, there were spots  
where the motor would not start.

I just replaced the whole player, it was quite old.  But, it was a very  
interesting defect that I still don't understand.  CDs start at the middle  
and spin fast, then slow down as they work out toward the edge.  Motor speed  
seemed to have something to do with the problem.


Re: CD Transport Rumble
Jon Elson wrote:

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And, reading the thread again, maybe the OP was talking about audible noise  
from the transport, not noise in the audio output, which was what I was  
thinking at first.


Re: CD Transport Rumble

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I had a cheap CD player (boombox) that only played the first 3 or 4
songs on any CD. It was not worth sticking money or time into it. I put
it in the barn for a barn radio (the radio worked fine). And bought
another CD player.  

I think the OP was talking about the CD itself making noise, not the
sound from the speakers. He said it's classical music. If it was rock
music, he probably would not even hear that noise. But I do wonder if
the center hole is not exactly centered. I'm sure that could happen....

Re: CD Transport Rumble
On 05/16/2017 02:35 AM, wrote:

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Hello, and thanks to all who responded.  I took a closer look at that  
problem CD and indeed the center hole is off center.  Not much but  
ostensibly enough to elicit the observed effect in the CD player.  
J. B. Wood                e-mail: arl

Re: CD Transport Rumble

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Yep, I had that feeling.....
The result of mass production....

Make a copy of it, and play the copy from now on. I'd copy at the
slowest possible speed because of that "wobble".

Re: CD Transport Rumble
On Monday, 15 May 2017 19:56:32 UTC+1, Jon Elson  wrote:
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Higher speeds are less affected by motor dead spots, at low speed it would see much more rotational speed variation.


Re: CD Transport Rumble wrote:

 It was odd, the beginning
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Yup.  I knew what an interpolation sounded like on that player, a little  
chirp when a block of data would not error-correct.  This was different, but  
maybe the player's chip set had some different method of covering up buffer  
errors that tried to fake the data.  And, I could easily see at the lower  
speed that it could get lots of buffering errors if the speed was unstable.


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