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Old 23rd January 2008, 04:22 PM   #11
diyAudio Member
 
Join Date: Nov 2007
Quote:
Originally posted by Algar_emi
Read that thread and included documentation. Turntable drive and speed control is a complex subject and there is no easy solution.
Search and read Mark Kelly excellent website. He explains all the tests he did to get the performance he wanted.

2007 Maxon Motor Group Buy
Thank you for the link - very informative indeed!

GD
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Old 23rd January 2008, 07:17 PM   #12
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Join Date: Nov 2007
Also got another idea...

Gonna try to get me hands on a B&O Beogram 1102 turntable (owned one 8 years ago)... it uses a rather precise DC motor drive system.

Want to see how they did it .
I know the motors were MATSUSHITA ELECTRIC (National Panasonic).

Even were fitted with a toroid tranny...

Sooooo .... will let you guys know....

Thanx for all the advice so far!
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Old 23rd January 2008, 11:08 PM   #13
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Join Date: Mar 2007
Quote:
Originally posted by GlidingDutchman
@ Error: Stepper motors can be used but I suspect they will mechanically induce a whine noise into the system. There is a guy however that converted a floppy drive's motor to run at 300 rpm.
Ahh, that's what I wasn't sure about. It seemed to me if they can be used to rotate a platter smoothly enough to extract a data stream at 15krpm, they should be able to do so at a few hundred rpm. As far as I understand, stepper motors don't actually move in steps, but have multiple coils and only a few stable states. Driven with the proper phases of sine waves, they should produce smooth motion.

Understood if the complications make it unworthy of driving a TT of course
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Old 24th January 2008, 12:54 AM   #14
hermanv is offline hermanv  United States
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Join Date: Apr 2004
Location: Northern California
To get smooth motion out of a stepper motor a technique called micro-stepping is used. In this idea not only are there sequenced drive pulses but each pulse has a current ramp up and down so the drive signal ends up looking more like a trapezoid.

Floppy disks are digital devices some cogging in the rotational speed is not important.

Most direct drive turntables were abandoned because of current spikes getting into the cartridge coils, they still tended to have micro instabilities, but most of all because they were hardly the simplest answer to the problem.

The only thing wrong with the model airplane motor idea is that no one in that industry is the least bit concerned about accurate rotational speeds. I think a musician can probably hear 0.1% error.
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Old 24th January 2008, 05:31 AM   #15
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Quote:
Originally posted by hermanv
The only thing wrong with the model airplane motor idea is that no one in that industry is the least bit concerned about accurate rotational speeds. I think a musician can probably hear 0.1% error.
I hear you regarding the airplane motors... but who knows? Maybe they do run stable? Maybe the controllers are tweakable... one thing for sure is those motors are very well made and dont cost an arm and leg.

0.1% Error can be irritating to any listener. My one prototype turntable's belt had a thickness diff and that caused a very sutle but audible "WOW" effect.

GD
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Old 24th January 2008, 05:03 PM   #16
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Join Date: Sep 2004
Location: virginia
Here is a motor controler from ZETEX design notes.

http://www.zetex.com/3.0/appnotes/design/dn26.pdf .

It doesn't have presets but it is simple.
Regards,
Ray
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