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Old 27th May 2012, 09:48 AM   #1
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Default Turntable rpms control

Hi all,
I want to construct turntable`s speed controller. This turntable is Unitra G-602 (made in Poland in 198x for USSR) and it uses 6v DC motor. Unitra`s native speed controller has a tachometer feedback, but stability is not good. I wonder, may I use controller without feedback? And which of them is much better in this case?
Thanks
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Old 27th May 2012, 11:14 AM   #2
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As a simple DC motor never gives fixed speeds, you'll need a speed controller with feedback, be it a tacho generator, an opto-electronic device or something like that. Otherwise you'll have to use a step motor, driven by a constant frequency generator.

Best regards!
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Old 27th May 2012, 12:12 PM   #3
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Thank you for reply, so now I have questions about tachometer.
Native controller uses photoresistor, little lamp and disk with holes on the motor shaft between them. Photoresistor is connected to stabilized voltage source.
As I understand it, photoresistor gives impulses, which should be converted into voltage, and this voltage should control motor. (comparator). But which form of signal gives photoresistor? And how to convert this signal into voltage, proportional to frequency?
Thank you.
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Old 27th May 2012, 09:48 PM   #4
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Not necessarily, Michael!

This is what I meant with 'opto-electronic device'. The photosensor gives impulses of a certain frequency at a certain speed. Compare this with a fixed frequency, e.g from a x-tal oscillator, and control the motor voltage via a PLL circuitry. That's all!

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Old 28th May 2012, 08:13 AM   #5
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Kay Pirinha, I think, PLL will be too dificult for me. As I understand it, PLL requies digital controller, doesn't it? Is it possible to build just good frequency meter, control the motor using it`s output and get good stability? So my turtable platter's mass is about 1 kg.


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Old 28th May 2012, 08:33 AM   #6
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Do not bother with that old turntable. My father also owned one. It is simply not worth it as the build quality is very bad. You can get e decent turntable of e-bay for about 50 euros with frequency control.
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Old 28th May 2012, 10:22 AM   #7
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rrrremus, I already have rebuilt tonearm, driving platter and belt are in very good condition, so I don't want to buy new turntable
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Old 2nd June 2012, 01:46 PM   #8
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Quote:
Originally Posted by white michael View Post
Hi all,
I want to construct turntable`s speed controller. This turntable is Unitra G-602 (made in Poland in 198x for USSR) and it uses 6v DC motor. Unitra`s native speed controller has a tachometer feedback, but stability is not good. I wonder, may I use controller without feedback? And which of them is much better in this case?
Thanks
Same problem here, obstacles for my diy tt. I googl everywhere to find solution for affordable tt motor controller using bldc or dc motor.

I think, I have to make a peace and live with what available. Dc motor with simple pwm controller and offcourse little math and a stopwatch
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Old 2nd June 2012, 09:08 PM   #9
Nanook is offline Nanook  Canada
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Default DC speed controllers and stable speeds

Hello.

Consider a very simple circuit but use good quality components, and ones that have very little temperature drift or whose circuit is temperature compensated. For checking speed something as simple as an appropriate strobe pattern and a red, or orange light source (as often used on direct drive turntables), but power the light source with a battery, or create a hand-held strobe light as per instrux on the vinyl engine. That way completely separate from the mains frequency. I use a hand-held digital tachometer and some shiny mylar tape. It provides readings that are +/- .005 RPM, so close enough for me (accurate to 1/100th of readings).
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