Optical Pickup Noise? [LD Player]

Discussion in 'Playback Devices' started by ChristopherDAC, Oct 9, 2004.

  1. ChristopherDAC

    ChristopherDAC Producer

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    My secondary player, an old CLD-V710 Karaoke machine built like a tank, makes an odd noise and I was wondering if anyone else has experienced this, and if there is a solution.
    Whenever it is playing a disc, i.e. when the laser is lit and focussed and the disc is spinning, there is a high-pitched noise. By comparison with TV noise I call it 10-12 kHz. This is easier to hear when a CD is in, since there is less motor noise. After putting in a CD, the TOC is read: the motor starts, and after a moment there is a series of beeps from within the machine superimposed on a high-pitched whine; then the motor stops again, and with it the noise. Press PLAY and the motor starts, there is the same series of beeps and then the continuous whine as long as the disc continues playing.
    This is rather distracting, and I don't enjoy listening to it. My CLD-D704 doesn't make this sound, nothing more than a couple of very faint R2D2 chirps as the focus servo finds its place; neither does any CD player I have ever used, nor [to my recollection] the old gas-tube player I got for a pittance. I've had it serviced and the optics realigned, by a Pioneer Authorised centre, on account of some other trouble, but the sound was the same before and after. So, is this unique to me?
     
  2. Leo Kerr

    Leo Kerr Screenwriter

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    I doubt it is the laser.

    I was going to ramble some more, but then I realized that my rambling would serve no useful purpose other than to repeat the above line: I doubt it is the laser.

    Best guess is that it would be some part of the laser tracking and focusing assembly.

    Other than that, sorry, no advice.

    Leo Kerr
     
  3. ChristopherDAC

    ChristopherDAC Producer

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    By all means, sir, ramble on! [​IMG]

    Any information of a technical nature I can get is helpful to my overall understanding of how the LaserVsision system works. I am well aware that a solid-state diode laser should not have any means to emit sound via its operation; but the phenomenon almost has to be centred in the optics assembly since it only occurs when the laser is on [and tracking is ocurring].
    My assumption is that some kind of tracking irregularity would manifest itself as a noise at a multiple of the rotational frequency, so that the pitch of the noise generated during CD play would change depending on playback radius [elapsed time] and for a LD with its higher angular velocity it would be pitched higher, perhaps beyond the range of human hearing; but neither case applies.
     
  4. Leo Kerr

    Leo Kerr Screenwriter

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    The laser tries to focus on a very specific spot on the disc. I'll be arbitrary, because I don't know really where it is, but, let's say that it's 1/4" inch from the lens.

    If the disc is uneven in any manner, shape, or form, the laser head adjusts the position of the laser 'cartridge'; in CD players, it's a tiny thing like a speaker coil, servo-locked to the SNR of the RF signal coming out of the decoder.

    Second, and more insideous, is the eccentricity 'correction.' If the disc isn't exactly centered - or, rather, the spiral isn't exactly centered, then the whole head module is constantly tracking back and forth (to some minute extent,) trying to track to the disc's spiral.

    To my knowledge, these are the only major adjustments that the laser head is having to make. That is, in addition to the actual tracking of the spiral (that is, the whole head assembly moving from center to edge as the disc plays.)

    If it's the general tracking of the disc, put in a long CLV disc. Does the pitch slowly shift downward as you play out toward the end of the disc? (On a CLV disc, the innermost ring holds about 1 frame of video information. The outermost ring holds something like 3 or 3.5 frames. Thus if it's the head tracking, it should pitch downward by that ratio.)

    For reference, on a CAV disc, the disc rotates at 1800 RPM. On the completely full CLV disc, it's 1800RPM - about 600RPM. (I can't remember CD spin rates.)

    I seem to remember more articles than this, but you might be interested in Bob Niland's legendary articles on the Laserdisc, partially (at least,) found here.


    Leo Kerr
     
  5. ChristopherDAC

    ChristopherDAC Producer

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    Thanks, I have 'em. As I said, the pitch of the noise is invariant with respect to the rotational velocity. CD linear velocity is about 1/10 that of [CLV] LD, and the outer radius of a CD is about the same as the inner radius of an LD, so since I hear the same noise no matter where I am in CD play and also when playing even a LD [CAV or CAV], I don't think it's the focus or radial tracking servos. My only thought is that there might be a resonance in one of the servos, some kind of feedback artefact which causes it to vibrate at about 10 kHz; but I think this would interfere with playback. Perhaps it is something in the electrical wiring? If this phenomenon is absolutely unique to my player I don't know what to think. I was hoping someone else had a machine which made some similar noise, and could compare notes.
     
  6. Leo Kerr

    Leo Kerr Screenwriter

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    Oh, my Sony MDP-455 makes all sorts of beeps and squeeks as it spins up and aquires the track-lock.


    Um, a strange thought just occurred to me. Are you sure it's a mechanical noise? That is, you're sure its not something coming out of the speakers? Seems unlikely, but unlikely things are known to happen..

    Leo Kerr
     
  7. ChristopherDAC

    ChristopherDAC Producer

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    No, it occurs when the player is the only thing I have turned on. No amp [I have one with a real power switch, so I know it's not leakage], no headphones, no nuthin'. It's also quite independent of what it's hooked up to, or indeed whether it's hooked up at all [being a karaoke player, it has a headphone jack, so I can use it independently]. Like I said, noises during the spinup seem to be quite common, but this high-pitched whine at a constant volume whenever anything is playing I haven't experienced with any other player.
     
  8. Leo Kerr

    Leo Kerr Screenwriter

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    hmm.

    Interesting.

    Better luck next guess, eh? I just wonder what that guess'll be...

    Leo
     
  9. greg_t

    greg_t Screenwriter

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    Have you tried popping off the cover, playing a disc, and listening to see if you can pinpoint it?
     
  10. ChristopherDAC

    ChristopherDAC Producer

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    The sound is high-pitched enough that it is difficult to localise. The only thing I can say about it is that it seems to come from the pickup, and that there is a one-to-one correlation between the sound and the activity of reading data from a disc. Note that when the laser is lit but not reading, e.g. if the player is searching for a disc and there is none in place, it does not occur.
     
  11. Leo Kerr

    Leo Kerr Screenwriter

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    This is really strange.

    If it were, for example, the laser focus-servo, I would think that it would be active during seeks.

    I've just looked back over the thread, and if it's in there, I've missed it: does it 'squeal' while in 'pause' mode - disc spinning, actively reading data off the disc (for CAV)?

    If it doesn't I'd begin to suspect something in the servos that drive the pick-up sled. If it does squeal in pause, then it's something within the head.

    Unless.

    Unless you've got a crystal and/or capacitor thingie going on somewhere else on the motherboard that isn't mechanical at all, but for some reason is flakey enough to be singing along with everything else. Seems a bit unlikely, but not completely impossible.

    I think what Greg was sort of suggesting was, if you pull the cover off the player, and as you're playing a disc, poke aroung (gently!) with a non-conductive, absorbant pad on a stick - say, an eraser on the back of a pencil.

    If you've a mechanical noise, and you touch it (even gently) to the noise-maker, it'll stop, right? Granted, as the pick-up assembly is on the bottom of the disc, it may be difficult to do this - although some players, especially the older, more tank-like ones, may be more inclined to operate upside down. (Unless you have a layer-flipping one, and can just do it from side 'b'. Actually, that's an interesting thing; if it IS a layer-flipping one, does it do it on the B side, with everything spinning the wrong direction?)

    Leo Kerr
     
  12. ChristopherDAC

    ChristopherDAC Producer

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    Sorry, it's single-side only. Yes, any play mode - free run, pause [blank screen], still, forward or reverse 1/90 speed, forward or reverse 3x speed, you name it - generates the same exact tone at the same volume. With the cover off it is LOUD!
    I guess it might be in the signal-processing section. I may try poking around inside there; if it's coming from one of the boards I might be able to damp it.
     

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