CED VideoDisc and Player Discussion

[7jlong]

Rixrex, your points are good ones, especially re: reinventing the (capacitance electronic) wheel. But I think there is a danger in guessing that anyone contributing to this forum are only the types that sit at home surrounded by a couple of vintage oscilloscopes and a pair of needle-nose pliers and thinks they can build themselves a new CED disc from scratch.

For example, I actually write this from my desk in my admin position at MIT. I don't know anything about what it would take to pull off a laser-etched CED, but a brisk walk a few yards in a couple of different directions would yield piles of people who might.

So no, I don't think it is 100% unattainable for forum contributors.

Which isn't to diminish the achievements of RCA at the time. I read Margaret Graham's book, and have read enough of Tom's research to know just how wild this whole process is. But the tools have changed since then, maybe to the advantage of just this very kind of medium.

I also think that anyone who would seriously try it knows that it is 100% for-fun only and hits the law of diminishing returns at the conceptual stage. Nevertheless, I can think of much crazier "flights of fancy" for someone to spend their time and money on. To suggest (as your post on 5/25 did) that any such endeavor is rendered invalid by a lack of scientific or societal advancement is defeatist at best and snooty at worst. If that were the case I should give up the bulk of the things that I do on the side for personal enjoyment, for they advance nothing besides my own sanity and enjoyment of life. How selfish!

[SRSanford10]

RCA researchers were eventually succesful at doing laser optical recording in the CED format. A major problem was the optical reflections from the v-shaped grooves. This was eventually overcome by careful control of the photoresist exposure. This same issue is common to the production of masks for integrated circuit production. Gaining expertise in this is valuable in numerous technologies.
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Scotty

[matt carr]

I think that since I'm not going to mass produce CEDs then I don't need to go through all the trouble of making the master and mold and stuff. All I would need to do is cut the stamper. If I can laser cut a piece of aluminum then that should work, I think. All I need to do is make a program to make a cut path or whatever a laser etching machine will take from a 60 minute or less movie file. That should be my next project. I got friends taking the polymer science classes at Southern Miss so I can get them to tell me all about what I need to make the discs out of and what the proper way to press them is.

If I get someone else to let me borrow their laser etching machine then all my costs should be in raw materials and whatever it cost me to make a press for the compression molding part.

As for making a program to basically transcode a video file from my computer into a cut path, that will probably take a year or two depending on how much free time I will have. I don't like having lots of projects laying around so I will try and finish it as quickly as possible when I start it.

[7jlong]

Again, I really know nothing, but I'm wondering why you wouldn't sidestep the stamping process entirely and instead etch directly onto a disc that would then be playable? If your recognized goal is not mass production, it seems like it would save you a lot of trouble to not have to go through the pressing process.

All this may look stunningly naive to a trained eye, but I think if I were going to pursue such a process on such a small scale I would probably try to find a way to make new blank discs and etch them directly. Kind of like CD-R for the CED crowd!

Just a thought!

[matt carr]

If that is possible - and I don't see why it wouldn't be - then that would be the way to go.

Now why didn't I think of that?

[SRSanford10]

I agree with 7jlong that cutting a disc that could be played directly is a much more reasonable way to start. I re-read an RCA CED paper in "RCA Review" for 1978. It went over the history of coated CED discs. The original coating was aluminum, but researchers found it was too grainy (this made for a poor carrier to noise ratio--and thus a snowy picture). Much better materials were gold and grain-free copper.
Early Philips optical discs were cut into a thin metal coating on a glass substrate. The papers I have seen did not detail the type of metal. About a year later, optical recording for laser discs converted to mastering onto a photoresist coated on a glass substrate.
Matlab has suggested using Chromium as the recording medium, possibly on a vinyl plastic substrate. The only negative thing I can see about this is that the melting point of Chromium is rather high. This should not be a problem if Matt Carr's friends have access to a powerful laser etching tool.
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Scotty

[Rixrex]

Thanks for the dubious compliment. I don't think I'm being snooty, and I also don't think it's defeatist to place differing priorities upon what one wishes to do with one's technical expertise.

Of course, anyone with the time, money and knowledge can do such things as recreate recording systems, even a simple cylindrical recording device to make recordings for playback on an old Edison machine. Certainly it can be personally rewarding even if there's no other value.

Regardless, viewing such endeavors on a personal level, it's a matter of what you wish to do with your life. Do you wish to recreate technology for personal enjoyment and think that you may find an advancement in such work, or do you wish to actually make scientific or technical advancement as your goal and experiment for that reason? I just don't think that recreating systems already created and now surpassed is particularly valuable, and great value and personal fulfillment can be obtained otherwise. That's the point I was making, and it isn't defeatist nor is it cavalier.

[7jlong]

Umm... OK.

Anyway, I'm intrigued by the materials that RCA auditioned and abandoned. Again, I'm very hazy on a lot of this - so forgive my ignorance - but based on my understanding of the system, does this mean that the material the disc is made of doesn't strictly matter as long as it is conductive? Is there a certain minimum level of conductivity that has to be met? Is too much... too much?

Seems like it would leave some interesting possibilities for materials choices if this wasn't a critical value in the equation!

[SRSanford10]

It remains to be seen exactly what the material limits might be. The ideal mechanical substrate for a contact playback system (phonograph, CED, etc.) should allow the signal undulations to be deformed during the passage of the stylus and then immediately spring back to their normal shape. If the substrate is too hard, the probability is that the diamond going by at 450 rpm's would tend to shear off the signal undulations.
For the electrical characteristics, there must be a capacitor formed. The gold coated stylus is the upper surface of the capacitor. The conductive surface of the record is the lower plate. In the early CED discs, the necessary insulator was made with a styrene plastic coated layer. This was no longer necessary with the production discs which use a formula with 5 percent of very fine grain carbon. The conductivity at 915 Mhz was stated as 5 ohm centimeters . This measurement quantity was new to me . The metal coated discs had a bit better signal to noise ratio than the conductive discs, but this was not enough tom be very significant.
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Scotty

[7jlong]

Interesting. I'm wondering if the kind of low-run manufacturing that we're talking about here merits an "upgrade" to the material - I'm sure a few of the decisions made as far as production of consumer CEDs were dictated by beancounters at RCA, as in: if you can get away with a more cost-effective material, then why not?

Perhaps any new CEDs could be seen as something like the 24k gold Mobile Fidelity Sound Labs discs - advanced disc materials for the discerning CED-o-phile! Ha!

[CLS2086]

[SRSanford10]

I ran across an article that would be useful in the event that a master recording could eventually be made in the CED format. First, a correction: I wrote in my last post that the CED discs which were sold to the public contained 5% of carbon fine particles. The figure was actually 15% carbon particles. The article was in "RCA Engineer" Jan./Feb. 1982 by Michael McNeely and Marvin Bock who were with the CED disc manufacturing operation in Indianapolis in the late 70's and early 80's. The paper is titled "Micro-molding is a VideoDisc requirement." The information is important for anyone considering trying to replicate discs in the CED format. Probably the most difficult specification to meet with this type of plastic molding process is a disc that is flat to within 10 one thousandths of an inch. RCA found what was in the late 70's the best European manufacturer of phonograph record presses. Their existing press would not meet this specification. The mold structure needed to be modified, and considerable work was done on carefully controlling temperature cycles and hydraulic pressure. The authors mentioned that compression presses for plastic molding has been used for years for such mundane objects as toilet seats, but I doubt that anyone cared if the toilet seat was flat to 10 one thousandths of an inch.
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Scotty