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How does linear tracking actually work?

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How does linear tracking actually work?

Postby chilsta » 06 Jul 2009 17:51

Hi All.

I don't really know how linear tracking works.

I've often wondered about this, but now thanks to the internets, I might actually find out.

I've searched the net and not come up with anything, so could anyone here tell me briefly how linear tracking works? Does the head get pulled along by the force applied to it by the groove in the record, or is it assisted somehow?

I know it can't just move at a constant speed, because records are pressed with differing gaps between the spirals of groove.
Having the head being dragged along by the groove just seems like it would exert too much pressure on the outward side of the stylus and ruin the sound reproduction.

Anyone know, or can point me in the direction of some further info?

Cheers
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Postby fscl » 06 Jul 2009 18:57

The majority use an opto - electro - mechanical sensing and servo motor tonearm drive system.

An interesting review of some tangential trackers is here:

http://www.vinylengine.com/turntable_forum/viewtopic.php?t=17131

Service manual for many of linears can also be found here:

Technics SL-7:

http://www.vinylengine.com/library/Technics/sl-7.shtml

Revox 790:

http://www.vinylengine.com/library/revox/b790.shtml

Sony PS-X800:

http://www.vinylengine.com/library/sony/ps-x800.shtml

Yamaha PX-3 schematics:

http://www.vinylengine.com/library/yamaha/px-3.shtml

Oh yeah almost forgot B & O:

http://www.vinylengine.com/library/bang ... 8002.shtml

etc....

This should give you a flavor of how linear tonearms work.

That said check out these tts from the D.I.Y. gallery:

http://www.vinylengine.com/phpBB2/album ... &full=true

http://www.vinylengine.com/phpBB2/album ... ic_id=7504

http://www.vinylengine.com/phpBB2/album ... ic_id=7148

The WPH is an air bearing tangential / linear, I'm still trying to figure out how this one works. :-k

I reckon your Sony is a VERY simplified / miniaturized PS-X800 with dashes of Technics thrown in. :)

It's fun to watch my SL-7 stand on end and have the tonearm travel up much like the PS-F5.

Hope this helps.

Fred
Music is Everything....Except Predictable....WFUV Fan.
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Postby YNWAN » 06 Jul 2009 19:07

Well. none of the high end, aimed at the' state of the art', linear trackers work in the way that Fred describes - they are all passive and rely on a very low friction air bearing (though the specific implementation varies) and the side force on the stylus in the groove to move them across the record (the Goldmund is a rare exception to this although the later arms may be different).
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Postby fscl » 06 Jul 2009 22:33

That's why I love this forum......

You can learn so much.

Thanks YN for making me search more outside of VE and come across this:

http://www.audiofederation.com/catalog/turntables/

:)

Amazing......without service manuals, I can only guess at how they work.

Fred
Music is Everything....Except Predictable....WFUV Fan.
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Postby olddude55 » 07 Jul 2009 01:35

I'm a dedicated SLT fan. My current main deck is a Technics SL-1210 sporting a Rabco SL-8E. Deck #2 is a Beogram TX-2.
Both turntables have servo arms; the groove pulls the arm slightly off-tangent (1/6th of a degree in the Rabco's case) and either closes a microswitch (Rabco), or moves a measured distance away from a photocell (Beogram), and this action triggers a servo-motor that moves the tonearm just a bit along the LP surface.
Servo arms sort of crab their way across the record, while air bearing arms stay tangent.
I won't go back to a pivoted arm.
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Postby nat » 07 Jul 2009 13:44

Some of the rabcos used a wheel on a rotating cylinder. As the arm moved out of tangency, the wheel moved with it so it drove the arm in the direction the arm was pulled towards. Very conceptually elegant, though perhaps not as accurate and quiet as some of the more sophisticated sensor systems. but clearly better than the cheap crude BPC systems.
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Postby olddude55 » 07 Jul 2009 23:48

[quote="nat". but clearly better than the cheap crude BPC systems.[/quote]

What is a BPC system?

Thanks
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Thanks

Postby chilsta » 08 Jul 2009 00:35

Thanks to all for your feedback-

Reading the linear tracking description in the PDF at the top of Fred's post made sense and shed some light, but didn't really explain how the opto sensing worked.

I've just taken the lid off my Sony to have a closer look & tricked it into thinking a record was inserted. Now I can clearly see how it works.
The sliding head has a laterally pivoted part which the cartridge is mounted to.
If I put slight pressure on the cartridge so that it pivots towards the centre of the record, the motor pushes the head assembly along the rail.
I can see there's a thin metal strip attached behind the cartridge which bends around behind it, then runs parallel with it. This arm is about 60mm long, then has a right angle with a 5mm length at its end. That 5mm passes between the optosensor's send/receive. As soon as the beam is unbroken, the motor moves the head.
I'm going to draw a diagram and stick it on my website as my description alone doesn't really do it justice.

I was going to ask how an air bearing worked until I saw this image. Is that the general idea behind all air bearings? Clever stuff. Both of the DIY ttables look incredible. Would love to see them in operation.

Olddude- do you have any images of your 1210 with its arm mounted? Would love to see that. I find it amazing that a microswitch can be as sensitive as on your Rabco. If someone described that as a concept I'd've said it would never work, picturing it just juddering itself along and wrecking the vinyl.

Thanks to all in this thread for demystifying something I've been wondering about since I saw my first linear tracking turntable some 20+ years ago!
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Postby olddude55 » 08 Jul 2009 01:31

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Postby JoeE SP9 » 08 Jul 2009 06:34

olddude55:
Being an old dude myself I had to figure out what BPC means.
Black Plastic Case Tada!!!!!
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Postby Beobloke » 08 Jul 2009 10:08

JoeE SP9 wrote:olddude55:
Being an old dude myself I had to figure out what BPC means.
Black Plastic Case Tada!!!!!


Actually, it's more often used to mean "Black Plastic Cr*p" :D
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Postby chilsta » 10 Jul 2009 14:51

olddude55 wrote:I think I can post a link that works...
http://www.vinylengine.com/phpBB2/album_showpage.php?pic_id=10090&user_id=51225


Wow- that looks great. Seen a few 1210 mods over the years (mostly DJ related), but never anything like that. Would love to hear it compared to a standard arm. Great work!
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Postby olddude55 » 11 Jul 2009 01:30

I have a lot of CDs of records I ripped with the Technics and it's original tone arm. Same cartridge, same phono stage, even the same interconnects (KAB RCA plate mod).
The SL-8E doesn't just smoke the stock arm; it rips out its heart and stomps on it. And the stock Technics arm isn't bad.
The difference hits you over the head, even when the CDs are played back on the crappy little desktop stereo I use at work.
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