I'm assuming the servo issues would be one of the biggest obstacles; it dawned on me that the ELP uses a laser to track the groove bottom, and that alone could possibly be used if one were to want to build one of these machines only for mono discs. But getting the laser to move with the shape of the groove at micron levels would be quite a challenge, I'm guessing.
I've actually done very very rough experiments with this, if you take a laser Pen, and point it at a grove while a record is spinning, you can see the difraction pattern change as the record spins, the problem would be translating these difraction patterns into something processable, and this would undoubtbly cause use of the D word (digital *gasp*)
As far as tracking is concerned, I was thinking of using the 3 beams from the laserdisc head. The middle one would sit in the bottom of the groove and do nothing. The two outer ones would straddle the groove and hopefully reflect off the 'land' area between the grooves.
Since the pickup head already has a photodiode array to detect these reflected beams, it might be possible for them to be used for this. One difference would be that the LP tracks are much wider than laserdisc tracks, so the 3 beam arrangement would need to be magnified.
If it worked, it would actually track similarly to the way laserdiscs and CDs track, with a beam on either side of the track. The servo attempts to keep the reflections from the two outer beams equal in intensity. When that happens, the center beam is centered on the track.
But as I said.. reading the signal recorded in the groove.. that's another problem entirely, and much more difficult for DIY, I think.
Since the pickup head already has a photodiode array to detect these reflected beams, it might be possible for them to be used for this. One difference would be that the LP tracks are much wider than laserdisc tracks, so the 3 beam arrangement would need to be magnified.
If it worked, it would actually track similarly to the way laserdiscs and CDs track, with a beam on either side of the track. The servo attempts to keep the reflections from the two outer beams equal in intensity. When that happens, the center beam is centered on the track.
But as I said.. reading the signal recorded in the groove.. that's another problem entirely, and much more difficult for DIY, I think.
pixpop said:
an understanding of the ELP principle may affect your assessment
the laser beams are in fact focused on each sidewall and the angle of the reflected beam is measured with a PSD (position sensitive photodiode) - the ELP player uses analog processing for the audio signal transduction path
galvo-mirrors are used for the high speed tracking - a separate stage does radial tracking
for more fun you need to consider physical limits such as the f#/gaussian beam waist dia/focal depth relation - in "light" of the knowledge that the better hyper elliptical line contact styli actually have a contact patch on the order your red laser light wavelength!
I think a laser phono cartridge might be a better approach - you can use those hyper elliptical line contact styli and a regular or linear tracking tone arm - well established tech - the laser innovation would be the laser motion transduction of a reflective spot on the stylus
pixpop said:
Yes, I think this probably is far more difficult than I could ever pull off, but I'm still taken with the idea...
I keep wondering if there's a way to combine the ELP approach and one of the other non-contact methods that reads the shape of the groove bottom for mono discs...again, you couldn't read stereo discs with it, but I wonder if it would be somewhat - in perspective - easier as a starting point. Except I can't fathom how the laser tracking the groove bottom could generate the signal without relying on some function of the servo, and then tracking and response would seemingly be limited by the servo's performance.
Just thinking out loud...
jcx is right that the ELP table uses the groove walls for tracking as opposed to the lands.
I've already mentioned it to van, but some DVDs use a wobble groove to store data - suggesting that a sacrificed DVD head may be a starting point for experiments. If it's a Blue Ray head you could get a much tighter focus from the beam than you will with the red lasers (although I'm not sure if they'll be implementing wobble grooves in Blue Ray). I had no reply on any of the fora I posted asking about the construction and function of wobble groove capable DVD heads, and none from a manufacturer mentioning them - which doesn't help.
Big project but I've been impressed by the diversity of this forum and am still hopeful that perhaps we might be able to work out something between us over time.
I've already mentioned it to van, but some DVDs use a wobble groove to store data - suggesting that a sacrificed DVD head may be a starting point for experiments. If it's a Blue Ray head you could get a much tighter focus from the beam than you will with the red lasers (although I'm not sure if they'll be implementing wobble grooves in Blue Ray). I had no reply on any of the fora I posted asking about the construction and function of wobble groove capable DVD heads, and none from a manufacturer mentioning them - which doesn't help.
Big project but I've been impressed by the diversity of this forum and am still hopeful that perhaps we might be able to work out something between us over time.
(Sticky Me?) Laser turntable
Hi
I've read many reviews, trade comments and 'testimonials' re this over the years. Most reviews started out waxing wonderment at the technology and terminating lukewarm at the sound quality.
Regarding the $15'000 price, I'm quite frankly surprised it is so low, seeing they claim to have blown $21million on R&D.
Secondly, if wealthy people spend the $15'000 bucks on this equipment and provided there are no breakdowns during their ownership, these owners will be the last to criticise their purchase, lest they are perceived as foolish. It is human nature that the more you money you spend on something, you become defensive in justification for that expensive trinket you spent so much money on.
A last thought: This laser tt can't handle unclean vinyl as the beams read muck as well. In fact, records have to be almost totally free of the usual stuff found on records before you can have an enjoyable and troublefree listen.
According to vinyl lore, besides decoding record grooves and turning into milliVolts, an analogue phono cartridge is supposed to also push the muck out of the way during play.
Why don't they just add a good quality line contact diamond stylus to their reading mechanism to push the muck forward or away and let the lasers do the job behind? Obviously the stylus will only have a suspension - nothing else. Something like a Stanton cart with the brush ahead??
bulgin
Hi
I've read many reviews, trade comments and 'testimonials' re this over the years. Most reviews started out waxing wonderment at the technology and terminating lukewarm at the sound quality.
Regarding the $15'000 price, I'm quite frankly surprised it is so low, seeing they claim to have blown $21million on R&D.
Secondly, if wealthy people spend the $15'000 bucks on this equipment and provided there are no breakdowns during their ownership, these owners will be the last to criticise their purchase, lest they are perceived as foolish. It is human nature that the more you money you spend on something, you become defensive in justification for that expensive trinket you spent so much money on.
A last thought: This laser tt can't handle unclean vinyl as the beams read muck as well. In fact, records have to be almost totally free of the usual stuff found on records before you can have an enjoyable and troublefree listen.
According to vinyl lore, besides decoding record grooves and turning into milliVolts, an analogue phono cartridge is supposed to also push the muck out of the way during play.
Why don't they just add a good quality line contact diamond stylus to their reading mechanism to push the muck forward or away and let the lasers do the job behind? Obviously the stylus will only have a suspension - nothing else. Something like a Stanton cart with the brush ahead??
bulgin
I came across a couple websites using desktop scanner to "read" the LP and some computer trick to "decode" the music and play it out from computer. My 2 cents.
http://www-cdf.lbl.gov/~av/
http://www.cs.huji.ac.il/~springer/
http://www-cdf.lbl.gov/~av/
http://www.cs.huji.ac.il/~springer/
Re: (Sticky Me?) Laser turntable
I have posted this a couple of other places in discussing this unit; the demo does seem recessed in the top to me, and others have commented on lackluster high end performance. Could this have something to do with loading on a standard preamp? I just wonder since the deadness seems to be in about the same range that the loading resisior would work on a standard cartridge, and I can't imagine what it would do to a laser input but degrade the signal. Just a thought....
I have posted this a couple of other places in discussing this unit; the demo does seem recessed in the top to me, and others have commented on lackluster high end performance. Could this have something to do with loading on a standard preamp? I just wonder since the deadness seems to be in about the same range that the loading resisior would work on a standard cartridge, and I can't imagine what it would do to a laser input but degrade the signal. Just a thought....
The scanner thing is what gave me a little bit of hope for this working - if you can get sound out of a horrible scan and some quick DIY software, you should be able to get at least something from this too.
The muck thing... the laser beams can be repositioned I think such that they avoid all the gunk at the bottom of the groove, leaving only big lumps and dust as the remaining problems. If you love music, your records shouldn't have big lumps of gunk on them in the first place. The dust could be fixed with something like a static charge plate across the record to suck up the dust (someone's probably already made one for normal decks) or an air duster.
The main thing that appeals to me about this idea in the first place is that it's none contact, so you don't have to worry about wear and tear. Using a stylus to dislodge gunk seems to go quite against that for me. If I was going to do that, I'd definitly just buy a normal cartridge and forget the lasers.
I don't think the sound quality (or lack of) from the ELP will be a fundamental problem of using lasers, it's more likely just their implementation of it.
And as bulgin says, if they spent 21M on the R&D, they're probably still 20.9M down on their investment given the number of these they've probably sold.
The muck thing... the laser beams can be repositioned I think such that they avoid all the gunk at the bottom of the groove, leaving only big lumps and dust as the remaining problems. If you love music, your records shouldn't have big lumps of gunk on them in the first place. The dust could be fixed with something like a static charge plate across the record to suck up the dust (someone's probably already made one for normal decks) or an air duster.
The main thing that appeals to me about this idea in the first place is that it's none contact, so you don't have to worry about wear and tear. Using a stylus to dislodge gunk seems to go quite against that for me. If I was going to do that, I'd definitly just buy a normal cartridge and forget the lasers.
I don't think the sound quality (or lack of) from the ELP will be a fundamental problem of using lasers, it's more likely just their implementation of it.
And as bulgin says, if they spent 21M on the R&D, they're probably still 20.9M down on their investment given the number of these they've probably sold.
This is all wild and fruitless speculation. So allow me to add to it:
If it were possible to track both edges of the LP groove, would it be possible to reconstruct the sound from these signals? I assume you would need to do some kind of magic with the amplitude and phase of the two signals. For example, if the amplitude changed equally, but they were exactly opposite in phase it should decode as a mono signal. I don't know what it would look like for a stereo signal. But the deviation from the center must bear some useful relationship to the signal, no? Is it necessary to capture the depth informationas well?
If it were possible to track both edges of the LP groove, would it be possible to reconstruct the sound from these signals? I assume you would need to do some kind of magic with the amplitude and phase of the two signals. For example, if the amplitude changed equally, but they were exactly opposite in phase it should decode as a mono signal. I don't know what it would look like for a stereo signal. But the deviation from the center must bear some useful relationship to the signal, no? Is it necessary to capture the depth informationas well?
pixpop said:
Hi pixpop. Don't know if I'm right or wrong here but aren't the opposing sides of an LP groove arranged to be sum and difference.i.e. one side does L+R and the other does L-R or something like that, the idea being that a mono cartridge can still play the lp? Stereo FM is transmitted in the same way for the same reason and decoded electronically whereas a stereo cartridge due to the arrangement of it's coils decodes the two signals mechanically. Si.
I don't think they are sum and difference. The two cahnnels are recorded at 45 degrees to the horizontal, and at 90 degrees to eacch other. The coils in the cartridge are mounted appropriately to pick up one signal and reject the other.
Easier than reading the groove with a laser might be capturing the movements of the cantilever. But there's no reason to believe a laser would do it better than magnets and coils.. except that the laser would have vast frequency response. I think frequency response of modern cartridges it not a problem, though.
Easier than reading the groove with a laser might be capturing the movements of the cantilever. But there's no reason to believe a laser would do it better than magnets and coils.. except that the laser would have vast frequency response. I think frequency response of modern cartridges it not a problem, though.
i got an old laserdisc player for free and so i decided to actually build one of these. what rpm does the laserdisc spin at? i thought that maybe i should get an old direct drive player and use the motor from that so it spins at the normal 33. any tips before i start?
Up to 1800 RPM (1798.2) for Constant Angular Velocity (CAV) discs. CLV discs start at that rate and ramp down to around 600 at the end. Like CDs, they play from the center to the outside. The motor velocity is under servo control.
Making it run 54 times slower at a steady rate will be a challenge.
G²
yeah i know its different, but its similar, and i can use the mount for the read/write head from the laserdisc to mount my own lasers and tracking system. i decided to just get an old broken turntable and scavenge the motor out of it. i think the hardest part is just getting it to track the groove...
What you want to look at on a vinyl disc is totally different from what is read off a LaserDisc. The reflectivity is drastically different for starters. LaserDisc, like CD, is looking for on/off 'pits' in one plane. For LP you need to look at the two sides of the groove AND an analog read out. It's a BIG job to re-engineer the optics and then the servos.
G²
There existed in the 1940s a turntable using optical playback. I cannot recall who made it (British origin I'm fairly sure), but the product was killed by the restrictions on purchasing of things like lead-acid batteries due to war.
This used an incandescent lamp as the light source, and a phototube (as used in a cine projector) as a pickup. There was no 'tracking' as such, the optics were moved by a plush-pad that rested on the disc, and was carried along by the grooves. Mono only of course.
There exist (existed?) photographs of it somewhere on the WWW a while ago, but I cannot now find them.
I have a 1960s Toshiba LP pickup that uses a diamond stylus, but also a filament lamp and photodiodes as electromechanical transducers.
Royal Dutch Philips demonstrated the first working version of their Laserdisc/Laservision system in 1972 (!) but it took them six years to get it to the form of a commercial player. Again, highly skilled engineers spending huge budgets.
I suspect an easier method would be to 'watch' the LP groove through a microscope with a CCD image sensor, and decode the variable image with software. Not analogue enough, perhaps?
This used an incandescent lamp as the light source, and a phototube (as used in a cine projector) as a pickup. There was no 'tracking' as such, the optics were moved by a plush-pad that rested on the disc, and was carried along by the grooves. Mono only of course.
There exist (existed?) photographs of it somewhere on the WWW a while ago, but I cannot now find them.
I have a 1960s Toshiba LP pickup that uses a diamond stylus, but also a filament lamp and photodiodes as electromechanical transducers.
Royal Dutch Philips demonstrated the first working version of their Laserdisc/Laservision system in 1972 (!) but it took them six years to get it to the form of a commercial player. Again, highly skilled engineers spending huge budgets.
I suspect an easier method would be to 'watch' the LP groove through a microscope with a CCD image sensor, and decode the variable image with software. Not analogue enough, perhaps?
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