Pete Verrando's CD Turntables

zuzu

#1 – 10:00 AM April 3, 2009

Doesn't Luomo have prior art on something like this?

Anonymous Anonymous

#2 – 10:10 AM April 3, 2009

I can bet, shiny metal visible pick-up is a fake, while real laser head looks absolutely traditional and is hidden underneath (probably covered by UV-transparent black plastic).

Will_Tingle

#3 – 10:22 AM April 3, 2009

An easy solution may be to put the CD on the turn table label up and have the stylus arm move across in sync with the real laser underneath, purely for aesthetics.

Either way, keep the Lazer in the arm, and I'd be more worried about the potential for blindness than the arc of the thing...

ROSSINDETROIT

#4 – 10:40 AM April 3, 2009

The earliest CD transports moved the laser in an arc. I have one apart on my bench: the elegant CDM-1 in a Revox 225 deck from the early eighties. The arc is short, though. The radius is no more than 4cm

RedShirt77

#5 – 10:52 AM April 3, 2009

they should replace the drives in xbox360's with these. Maybe they wouldn't self destruct every 2 years like the current ones do.

strider_mt2k

#6 – 11:02 AM April 3, 2009

Lazer arm?
Blindness?

I'm listening...

dculberson

#7 – 11:07 AM April 3, 2009

I bet the arc wouldn't really interfere with reading much at all. The CD transport mechanism is pretty robust at this point, and can deal with a lot of error. The difference on a track by track basis would be pretty minimal.

I bet you could just gut a portable cd player, modify the mechanism to swing a "tonearm" instead of moving the linear slide assembly, put the laser at the end of the tonearm and have it work.

That's all 100% conjecture, though, so take it for what it's worth.

I'll go out on a limb and say that's how these were built. Just the insides of a commodity portable CD player rearranged with a different mechanism for moving the tonearm. The little cheapie LCD screen seems to support that guess.

ROSSINDETROIT

#8 – 11:08 AM April 3, 2009

Unlike phonograph albums, CDs read from the inner edge outward. In this way they're able to accommodate different size disks on the same transport without sensing the medium size before reading. Sort of destroys the illusion when you can see the CD being read that way. I do like the idea of exposed optical media but in some cases ambient light can interfere with the read head.

ROSSINDETROIT

#9 – 11:13 AM April 3, 2009

Head positioning on optical media is not a trivial issue. Adjacent 'tracks' are *really* close together. It requires quite precise control. That's not to say that the whole positioning mechanism couldn't be outboarded to a en external 'arm' positioned over the disk.
Why does the 'tonearm' in the player in the photo have a finger lift? Like you're going to cue up a track to play. The CD player has to read the inner track for various information of the disk before playing anything.
I'd have to do a LOT of research before attempting something like this and I suspect the first thing I'd find is it's been done.

dculberson

#10 – 11:21 AM April 3, 2009

I figured the finger lift was just for style.

Harrkev

#11 – 11:48 AM April 3, 2009

#9) These days, head positioning of an optical media IS a trivial issue.

The head just has to be "close enough" to read the track. The lens in the laser assembly actually swivels, which allows it to make the last little bit of adjustment needed to track the data, so the actual mechanical portion does not need to be astronomically precise. This is because the mounting hole in the middle of the CD may be a little bit off. The player need to be able to track data that "wobbles" a little bit. The whole thing is closed-loop, so the "arm" always knows which direction is has to go to maintain the data.

I would imagine that the mechanical portion would need to be smooth (high quality gears and bearings), as any mechanical jumps would result in skipping.

The *REAL* problem is that a CD player uses a laser -- an infra-red (invisible) laser. CD players are required by law to keep the laser turned off unless the cover is closed. Check any CD or DVD player for the laser warning sticker. I am sure that a simple CD player does NOT have the high power needed to blind somebody, but it is better to err on the side of caution when dealing with infra-red, simply because if it IS blinding you, you cannot see it. While something like this COULD be made, I do not see it being approved for sale for due to violating some consumer-safety regulation.

Anonymous Anonymous

#12 – 2:34 PM April 3, 2009

Funny nobody has mentioned this yet, but as a CD player is reading data, it's not so sensitive to arc/radial readout - just so long as you can follow your track and the buffer doesn't run out. Sometimes digital just seems to take the challenge outa things...

felsby

#13 – 2:56 PM April 3, 2009

Most Philips drives moves in an arc.

nixiebunny

#14 – 3:30 PM April 3, 2009

Here's how the CD pickup mechanism works, and why this turntable would work.

The CD pickup has three major parts: a laser, a lens and a photodetector array. The laser makes light that's sent through a beamsplitter to the CD through the lens which focuses the light into a tiny spot on the data track and back to the photodetector array.

The focus/tracking lens is usually mounted on a quad of springy wires that allow it to move up and down for focus and laterally for tracking. A pair of tiny linear motors (coils of wire working against rare-earth magnets) move the lens very quickly to compensate for focus and tracking errors. Two servo systems act on error signals from the photodetector array to supply the necessary lens motion commands.

So the pickup mechanism that's mounted in the standard $20 portable CD player could easily be adapted to work in jut about any configuration; it just needs to be held roughly over the correct track at roughly the correct distance to focus.

The "tonearm" concept would work just fine, assuming that it has a servo motor to keep it within the tracking correction range of the lens system. The tracking error caused by the lens rotating is only a small cosine error in the tracking gain, so it's not likely to cause servo problems.

The laser beam will reflect into your eyes if you're not careful, so this design would definitely not pass safety acceptance testing.

ROSSINDETROIT

#15 – 6:20 PM April 3, 2009

I had to go take apart a Sony portable to confirm this. Yup, it'll work. Now project number 67 on my life list.