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From: wjm@whuxj.UUCP (MITCHELL)
Newsgroups: net.audio
Subject: Re: Unwarping records
Message-ID: <186@whuxj.UUCP>
Date: Thu, 12-Apr-84 08:49:43 EST
Article-I.D.: whuxj.186
Posted: Thu Apr 12 08:49:43 1984
Date-Received: Fri, 13-Apr-84 20:15:24 EST
Organization: Bell Labs, Whippany, N.J.
Lines: 69

Yes, the plate glass sandwich technique will work for unwarping severely
warped records, BUT BE CAREFUL!!!!!'
First, be sure the glass is perfectly clean, since any dirt on the glass
will flow into the record's surface and cause surface noise (why do you think
the regrind vinyl used by certain major U.S. record companies is so noisy -
the ground up label paper and dirt from it is one reason).
Second, as mentioned earlier, the key to the process is to warm the record
slightly so that it will flow back into a level plane, but not too much so that
the information in the grooves is distorted.  Since records have raised outer
edges and center areas (to protect the grooves when records are stacked on
a (horrors ! (-: ) changer) the pressure from the glass plates will be applied
there rather than to the grooves.
It is CRITICAL not to let the record get too hot for too long, else groove
damage will occur.
By the way, an alternative to this procedure is to put the sandwich of glass
and record in bright sunlight, which will accomplish the same result.
(There is a lesson here - keep records (and tapes for that matter) out of
the bright sun, especially in an enclosed car).
It is important to keep one thing in mind - the glass sandwich procedure should
only be used as a LAST RESORT when all other alternatives have failed, namely
putting the warped record in its jacket or between glass plates under some
record-sized weight (like a stack of other records), using a center weight on
your turntable, and storing it in a horizontal or vertical stack for some time.
Like most other things, an ounce of prevention is worth a pound of cure and
proper storage will keep most non-warped records from warping.  The best way
to store records is exactly vertical, but if you can't accomplish this, storing
them horizontally in stacks is a reasonable alternative (although less
convenient when you want to play the bottom record in a stack- perhaps some
CS stack allocation algorithms for ordering the records might minimize this
possibility) (By horizontal and vertical, I am refering to the plane the LP
resides in).  Also, I highly recommend a center clamp/weight - they are not
that expensive (~$20) and can make warped records much more playable.  Also,
I view the ability to play severely warped records an important criterion
when selecting a new arm or cartridge - note that it is not totally correlated
with price, while most high-end arms do well, there are budget models that
also perform well - at one time I had a Garrard Zero 100 that did quite well
in this category (athough it had many other problems, which was why I upgraded
through several intermediate steps to my Mission 774/775).
Of course the only answer for NEW warped records is to keep bringing them back
and keep letting the guilty record company know that this type of defective
product is not acceptable.
While we're on the subject, don't forget that TAPES can also be damaged by
improper storage and high heat, which can warp cassette shells and (in extreme
cases, damage the plastic tape backing itself).  If you do have a damaged
cassette, Radio Shack sells a cassette repair kit (sometimes known as a C-0)
which is a new shell and leader tape that you can splice the tape from the
damaged shell onto and wind it into the new shell - yes it is a pain, but it
is a way to recover a damaged cassette.
Open-reel tape is probably the medium least susceptable to physical damage
(as long as the tape itself is ok - it can always be wound onto a new reel)
Of course, all magnetic tape is subject to stresses in the tape pack, which
it why one should NEVER store tapes that have just been fast forward wound
or rewound.  It is also advisable to store tape in the PLAYED position (tail
out) since this makes any "print-through" (the transferring of magnetic
fields containing information from one layer of the tape to the one next to
it on the hub) appear as a "post-echo" (an echo after the original signal)
which is less objectionable than a "pre-echo" that would result if the tape
were stored in the ready to play position (head out).
Tape is also subject to magnetic damage and should be kept away from items
containing magnetic fields like power transformers, motors, solenoids, relays,
and the like (not to mention bulk erasers and head demagnetizers).
As for CD's, I'd suspect that they can also be warped by heat to the point
where they can't be tracked.  Since they are rather new, I don't have
any quantitative data about susceptability to damage or repair methods, but
it seems that the same type of care should be given to them as to LP's or tapes.
Regards,
Bill Mitchell
Bell Communications Research, Inc.
Whippany, NJ (whuxj!wjm)