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Old 9th March 2007, 02:15 PM   #1
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Default Micro Seiki BL 99V - turntable Power Supply

I am new on this forum so please excuse all unsual behaviour.

I Search schematic(s) for high performance servo speed power supply for DC motor for Micro Sieki BL 99V turnatble.

Original design based on custom IC w/o marking assocoated to
DC motor (7.5 Volts) who is comounted with tacho generator delivering # 610Hz signal @ 331/3 RPM. motor / platter transmission via flat belt requires smooth acceleration to avoid forth and back corrections.

In advance thank you!
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Old 10th March 2007, 01:06 AM   #2
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Default You won't find one

Unless you find a unit that Micro Seiki produced for this table, I doubt that you will be able to find a suitable supply.

This is because the supply you seek must be designed around the table itself. Such a supply is effectively a phase locked loop with the VCO in the loop being the frequency generated by the tacho in response to a drive voltage. The response time of this VCO must be taken into account in the design of the PLL and that's no trivial task.
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Old 10th March 2007, 06:49 AM   #3
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thank's

You are right I will have to dig into my electronic lectures...VCO /PLL are quite far away from my today job...

Do you think PIC based controlled power supply using PWM to drive the motor would present more flexibility to adjust speed accuracy, and correction slope??

I fact Iwas thinking about measuring the tacho period (counting)and comparing result vs. set value and correcting by variable incement of PWM + delay + wait time to take into account the global system response time (platter inertia +belt stess).....

What worry me is the jitter a noticed at tacho output, Yet I have not been able to identify if it real speed jitter or possibly due to construction (the tacho frequency is 40 times the rotation speed) could the coil winding /positioning be the cause ( a bit like in selsyns aimuth encoders)

Jean pierre
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Old 10th March 2007, 06:59 AM   #4
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6 months spent trying to wrap a brushed DC motor in a PLL loop and failing miserably has convinced me that jitter on the encoder output is your worst enemy.

One "fix" is to embed the VCO in a separate PLL loop so the filter on the output can de-jitter the original encoder signal. Unfortunately the second loop filter adds to the delay through first loop making that circuit even harder to design.

The added complication of a brushless drive would make me run away fast.
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Old 13th March 2007, 03:42 PM   #5
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I Mark,

Looks like you have been confronted to the problem,

before I give up with this turntable I am tempted to measure (and record) N successive periods of the tacho signal (at least over one platter rotation to see if that jitter can be characterized.

Is it be time correlated or motor shaft position correlated or platter position correlated. or ...any other ?

First measurements with a logic analyzer (# 10 tacho periods) were not really conclusive but the frequency ratio between tacho signal and motor rotation makes one - even 10- tacho periods corresponds to few rotation angle degrees.

If this approach gives some sensible results then I think a lookup table could be used for correction.

Have you any opinion about this method ?
Jean pierre
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Old 13th March 2007, 04:01 PM   #6
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Change motor for a Teres unit?

Arne K
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Old 13th March 2007, 04:31 PM   #7
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Thanks for the advice ,

You are right if I was a reach man...unfortunately I am not

Definitely I will not pay 700 $ to repair a turntable I bought 15 years ago for about that price (vaccum platter and MA 505 tonearm included)

But their website gave me some ideas on how add a stroboscope type speed measurement to have the platter real rotation speed and fluctuations.

I am still willing to solve the problem through a DIY approach. Lets call it a challenge.
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Old 13th March 2007, 07:19 PM   #8
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I would not bother much with the strobe, other than use it for manual adjustment/display.

And maybe go for Mark Kelly's motor-control.


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