wjm@whuxj.UUCP (MITCHELL) (04/12/84)
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)
chenr@tilt.UUCP (Raymond Chen ) (04/13/84)
<Sacrifice>
First, of all, thank you Bill Mitchell. I was going to post an article
like yours regarding unwarping records, but I was hoping that someone else
had beaten me to it.
I'd just like to add one thing. Make sure that the protective groove will
be the only thing in contact with the glass if you're going to use the oven
method. I've seen records warped in such a way so that the portion of the
record with the grooves would have made contact (and recieved most of the
pressure) first, including one that looked like someone had heated their
thumb to 200 deg C. and then stamped the record with it. (Weird).
I still think you're better off trying EVERYTHING else before resorting
to this method, though.
--
From the Random Fingers of --
Ray Chen
{allegra | ihnp4 | mhuxi}!princeton!down!tilt!chenr
"It's amazing what a thousand monkeys and a few typewriters can accomplish..."ron@brl-vgr.ARPA (Ron Natalie <ron>) (04/13/84)
My favorite method from my FM radio days is common through out the industry. Most of the broadcast quality turntables use massive platters for both durability and stability. The method involves a weight the size of the record label with a hole in it that is placed on the record while playing. Other methods include a similar "spider" device that uses spring tension rather than sheer weight. A few years ago, someone came out with a turntable with a vacuum pump that sucked air through the platter and could apply some phenomental amount of suction to hold the record flat to the platter. I don't think it ever caught on. I think I'll stick with the record weight and a tone arm that is sufficiently low in inertia to track the remaing wrinkles. -Ron