Quit true. In fact, the FBI came to my house because there seemed to be some price fixing going on in the film cap business with a few with high mark up that caught the governments attention. true story. The markup on boutique caps is excessive and one in particular who started that trend was linked to me by association. Dont know what became of it but the person they were really investigating doesnt sell caps any more. However, that started a trend.... not unlike headphones are marked way way higher than costs would traditionally indicate. A lot changed politically since then and now Greed is good, it seems.
THx-RNMarsh
Regarding the 2H which was measured by FFT on the captured cap DA waveform from a film cap.... it is real. And, yes, the traditional model is linear. I have not explored the root cause of that 2H but it was lower with lower DA caps. Some how the model needs to be refined more.... perhaps to show some asym hysteresis. My test used a pulse because it ws not a symmetrical sine wave..... I wanted a transient... more music-like... waveform.
Those who listen to caps for any sound has been consistant over the years in choice.... that choice follows the DA of caps... lower DA is chosen via listening evaluations. I use PP most anywhere for a film...
But to put this in historical context, we had a lot of coupling caps which were polar types and that was the issue at the time... polar cap DA is huge and more audible. That eventually led me to the idea to create only balanced topologies and then servo them. This the mainstream today and thats how it came about.
Today, it is the DA you have to worry about in filters where there is a voltage drop across the cap.... speaker XO, active EQ, RIAA, NAB etc.
THx-RNMarsh
Those who listen to caps for any sound has been consistant over the years in choice.... that choice follows the DA of caps... lower DA is chosen via listening evaluations. I use PP most anywhere for a film...
But to put this in historical context, we had a lot of coupling caps which were polar types and that was the issue at the time... polar cap DA is huge and more audible. That eventually led me to the idea to create only balanced topologies and then servo them. This the mainstream today and thats how it came about.
Today, it is the DA you have to worry about in filters where there is a voltage drop across the cap.... speaker XO, active EQ, RIAA, NAB etc.
THx-RNMarsh
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with laser pickup, you can not use a fixed amount of spiral tracking motion to stay centered on the groove due to those mentioned variables. isnt trivial to drive it along the groove with just light. This was the area they had trouble with and then the whole idea died. Did they ever get it solved?
-RNM
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The Library of Congress has sponsored that, there are results.
http://bio16p.lbl.gov/2013-examples.html
EDIT - If you search around the home page there are some old presentations with clips from original LP, laser scanned LP, and CD remaster from original tapes. I assume the cost of the equipment is 100's of K$
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They don't, they use an elaborate tracking system like CD or DVD which has exactly the same problem. I'm sure they borrow heavily from that technology.
I believe there is a linear tracking carriage for the optics and then glavo mirrors are used to steer the beams to track the lateral low frequency wiggles
extra beams are used to find, track the groove edges so the wall sensing beams can be focused to spots on the groove walls
the output is the reflection angle of the wall spot beam - works out to be proportional to the velocity in the small angle approximation
linear position sensitive diodes are used to for the reflected beam sensing
so the output really is real time, real analog
extra beams are used to find, track the groove edges so the wall sensing beams can be focused to spots on the groove walls
the output is the reflection angle of the wall spot beam - works out to be proportional to the velocity in the small angle approximation
linear position sensitive diodes are used to for the reflected beam sensing
so the output really is real time, real analog
For the record, awhile back, due to discussion on this thread, my associate (my layout guru) and I looked into using FR-4, and we found that there were SOME acceptable versions that will will most probably use in future, as we are always designing new products. Teflon IS expensive, but it does do well, sonically. If we do not use FR-4(best type) in future, we might use what Nelson Pass uses, which is a ceramic. It looks good too.
Did they solve it satisfactorily and at reasonable costs -- at least comparable to CD drives? That would then make it more interesting possibility.... without the wear of the Lp it would have a great boost to the industry -- if at 'popular' prices.
THx-RNMarsh
A few years ago I chuckled about a friend who is certain that he hates feedback, one who embraces the dreadful and unsupported notion of canine tail-chasing, who nonetheless loved his laser turntable---except for some peculiar effect close to the end of a side, which led him to get rid of the machine. Thorsten L. slammed me for this and said the laser pickup was a simple photodiode and the tracking servo was slow enough as to have a negligible effect on the audio output (TL I hope I am not misquoting you here).
I also questioned the problem of speckle and was assured that it was a non-problem. In case it might ever be, there was a recent development in making relatively broadband light sources as scene illuminators that might have application.
The one thing that virtually everyone I've read who has dealt with optical LP players cites is the need for absolute cleanliness. Since this is difficult to achieve (look at the dust motes in a beam of sunlight in any typical environment to see what one is up against), I can see laser players used in archival facilities, but perhaps just a curiosity for home use.
What I do find a bit odd is the extent to which people are willing to suppose that light is so fine-grained, as it were, that to do anything with it in lieu of, say, electrical signals is prima facie desirable. Of course supermarket scanners work, but the resolution is not high. There is a lot of exciting work going on in beating certain supposed resolution limits in microscopy, but in general unless you are dealing with photons as the signal of interest to begin with, the introduction of them into a system is not always an assurance of enhancement.
Brad
And where exactly did this "DA waveform" come from? How were you able to isolate DA from everything else in order to attribute the distortion to DA itself? How were you able to distinguish the source of the distortion from all other possible sources of distortion? John's "micro diode" distortion was simply distortion produced by his antiquated test gear.
And did you not read Scott's comment or Jan's Bateman quote? Do you have even the foggiest notion of what you're saying?
Or not. Maybe you've just come to erroneous conclusions.
Why not use difference testing and use actual music?
Oh get off it, Richard. I doubt you could tell the difference between an electrolytic and a film cap without peeking.
Again, read Scott's comment and Jan's Bateman quote. I really don't think you have a clue what you're talking about. Just more clown car mythology.
se
A lot of discussion on error correction lately.
Some of you might be interested in this,
http://www.diyaudio.com/forums/lounge/273459-cd-error-correction-audible.html#post4304371
The first time I saw teflon in a product was in an ADI op amp, the metal-cased 310 (? --- sure that number has been recycled a few times now). The high-quality input terminal was insulated by a teflon insert in the cover plate. The product used the varactor bridge approach and the diodes were selected bipolar transistors! Someone at UCLA had designed the amplifier into a photometer, with the detector being cooled photomultiplier tubes.
When I breadboard with through-hole parts I use bus wire and teflon tubing---not for the high resistance etc. but because teflon doesn't melt back like lower-temp insulation. I suppose I'm probably getting a whiff of perfluorooctanoic acid from time to time, but it hasn't killed me yet.
For a self-scanned photodiode array spectrometer, the charge-integrating preamp used a feedback C fashioned with teflon tubing and with one "plate" being the input JFET gate lead. The cold chamber was evacuated and the temperature stabilized. The capacitance was determined by two independent measurements to be 130fF if memory serves. A lot of charge to voltage conversion gain. Needless to say when using the system for spectrometry, there were standard stars observed for additional calibration.
I believe that Michelson-Morley is the point at which much of modern particle physics pivoted. Before that, of course, it was widely assumed, since at least the Greeks, that all matter and energy manifestations were built upon a common Aether medium. The unexpectedly null result of the Michelson-Morley experiment to prove the Aether was taken to mean that an Aether did not exist. From that, Lorentz equations attempted to reconcile the null M-M result with known relative velocity principles. Hence, the birth of Special Relativity theory, with time dilation and mass increase predictions.
However, the way I've read it explained before, there was and is another interpretation to the null Michelson-Morley result. Which is that an Aether (if it exisited) could be of a nature which would not apply a drag or resistance on matter and energy. Water or air would be the wrong fluidic medium analogy. An Aether would instead have behave like an analog of a true superfluid, applying zero motional resistance to matter and energy, if in fact such a medium were to exist. This would have to be so, else the orbiting of planets would eventually slow and decay. I don't believe that the original M-M experiment, nor a higher resolution modern re-creation of it, could have proved nor disproved an Aether having such a superfluidic like property.
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Despite the fact that I've been running several projects to eliminate PFOA from any of the products my company sells, I'm personally not terribly worried about it.
The issue with PTFE as sleeving is triboelectric effects. That's an acute problem at high impedances.
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