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Old 3rd March 2013, 12:44 PM   #61
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These are the very cheap stepper motors I found in the PDF . Years ago I found another link to someone who had converted similar ones to AC ( now it's lost ) . When I wrote to him he said it is no big deal and just needs a capacitor to make it work . One might guess 4.7 uF ? I have no idea exactly where this would go . The construction of the motors looks identical to the over priced turntable versions . Seems worth trying ? Conventional DC stepper drive I suspect is no worse ? There is no magic about motors like this . To be honest none are really right for a turntable . The AC hysteresis type is better . These are rare . I made my own for 501 ( stock parts converted from a centrifuge motor , 30 % not used ) . It had a 28 W rating .

The strange part about a hysteresis motor is the phase shift is by a magnetic distortion created by short circuited turns of copper ( shaded pole ) . This is not the 90 degrees it might ideally be . It is less . However the way the rotor follows the circulating magnetic field with a slip angle greatly helps . When loaded it is like an elastic link pulling things along . A stepper fights all the way which never allows the motor to be part of a damped system ( the belt can do that , usually too well ) . The vibration of a hysteresis motor is high , however it is often lower than a stepper of a given power . A bit like saying a V8 is better than a single cylinder engine whilst not being a turbine . V8 will do nicely . I don't say straight 12 as I suspect we don't get that far . Multi-motor might if mechanically timed and joined do some of that . That is not as difficult as it might sound .The motors almost by the way they are made will self align . Just using the lead out wires as a timing reference probably will be good enough . The motors automatically jump to a pole position .

http://www.rapidonline.com/pdf/37-0507.pdf
http://www.rapidonline.com/Electrica...8-5d7ffd919ca0
http://www.cas.mcmaster.ca/~lawford/...ef/Stepper.pdf

Last edited by nigel pearson; 3rd March 2013 at 12:53 PM.
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Old 4th March 2013, 02:31 PM   #62
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This is the text I found before . There is much to commend in his turntable . The motorcycle valve is a good idea . Motors also .

The Altmann DIY Turntable
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Old 5th March 2013, 08:18 AM   #63
msdin is offline msdin  United Kingdom
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The only turntable that uses a stepper motor that I know about is the Phonosophie No.3.
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Old 5th March 2013, 12:56 PM   #64
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There are a few ? Nottingham Analogue I believe ? The point is as the sine wave enters the magnetic circuit it becomes squared . Thus a synchronous motor is just a stepper working at 50 at 60 Hz . Steppers have a resonant frequency which is best avoided . 50 or 60 Hz I suspect is an easy frequency for a stepper . The stepper if so is a very cheap source of a good motor . The one I gave as an example will work up to 0.5 A approximately ( at 12 V / phase ) . That looks to be more powerful than many . There is scope to play with the power verses vibration if so . My guess is 8 V rms will drive it if a sine wave . Also one can try a different frequency . A triangle wave might work well ?

It might even work from a NE555 timer if discharge transistor is connected to output . That gives up to 400 mA .
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Old 6th March 2013, 11:01 AM   #65
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Here is the big Crouzet synchronous . About 11 watts , used by Avid I believe ? This is typical of all synchronous I have taken apart . Not shown is a spring and nylon thrust washer which often is noisy ( bottom of the motor ) . If you notice the phasing is just the shaped metal triangles . The coils are very simple . If you beak open a motor you often can join it using standard solder and plumbers flux . The iron has to be very hot and the zinc filled off . As my brother proved many times steel will just about solder . The advantage is not so hot as to cause problems and will retain any adjustments .

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Last edited by nigel pearson; 6th March 2013 at 11:04 AM.
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Old 7th March 2013, 05:18 PM   #66
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I didn't want to leave this thread without an answer to a question I posed . Can a stepper motor make a good synchronous motor ? I bought one of the motors from Rapid . Less that one hour later I had all the answers I needed . The simple answer is yes it does make a nice motor . I only used a holding it and voltage meter test ( equal voltages seem to indicate phase shift about right usually ) . As far as I can tell at 6V rms 12 uF is ideal ( 10 uF used ) . 12 uF was a pleasant surprise as it not too expensive . The transformer I list is what was in my useful box . I suspect the ideal transformer would be 12 V 6 VA . I would use a series resistor into the primary side to drop the output to < 11 V rms . I would do it to the primary so as to lower waveform distortion . Cheap transformers are bad on that . A light bulb might do well ( 15 W ? ) . Consumption is about 100 mA x 2 at 8V 50 Hz ( slightly less than expected , almost a clone of the famous Airpax I list ) . I calculated 78 Hz as the point where I expect the performance to drop if going the electronic route using a Quadrature oscillator and power amp . I would imagine LM324 ( MC33079 ) and 2 x BD135 and 2 x BD136 to be workable . It is possible that no heat sinks would be required . Thoren's used un-biased class B for the TD125 . If a 51R feed forward resistor was used I suspect distrotion would be low . 78 Hz is the the calculated for a steeper on square waves ( 390 RPM ) . It should work better on sine waves and might go higher .
http://www.daycounter.com/Calculator...lculator.phtml

From what I can tell this motor is very much like this ( old Airpax = LP12 ) .
Buy AC Motors Record deck synch motor,250rpm 110V McLennan Servo Supplies 9904 111 31813 online from RS for next day delivery. ( plus 11 tax )

Chassis Transformer 230V 6VA 12V+12V
12uf Plastic Case Motor Run Capacitor
http://www.rapidonline.com/Electrica...8-5d7ffd919ca0

The 12 uF is a bit OTT . Any film type will do .

Last edited by nigel pearson; 7th March 2013 at 05:46 PM.
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Old 8th March 2013, 12:10 PM   #67
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Here is a quadrature oscillator . Change the 22/10M resistors . I used an LM 324 . It gives very good performance all things considered . The chip shown needs 30 pF compensation caps , not so LM324 . I did try to make a simple power amp to drive the motor with the spare sections . That was less happy . A gain of about 30 for each of the power amps ( TDA 2040 ? ) . The distortion is remarkably good for such a simple circuit . I used 47 K where is says 50 K . Notice I was not close to 50 Hz . It needs tweaking to get right . The impedance of the chip makes a difference . TL074 might be closer to the calculated values .

I tried out the primary size resistor . 10 K does it well ( 2 W 500 V ) . The waveform looks none too special . Gives about 7.5 V if so . This 9V one gives nearly 11.5 V at this load in the UK .

In a rush now so forgive typo's .
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Old 8th March 2013, 03:31 PM   #68
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Interesting stuff, Nigel. What about a Bubba Oscillator? Is it over-kill or not work in this application?

Bubba Oscillator | Simple Circuit Diagram

Thanks for your work so far.

Vince
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Old 8th March 2013, 07:05 PM   #69
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High Vince . I used a version of the Bubba called a State Variable Filter for the Garrard 501 . The ESP site shows something very similar . 91K and 10K resistors cancel the third harmonic . That will give about - 66 dB distortion . I was very impressed by the simple Quadrature above as it is giving - 57.5 dB . This is not a simulation . That is so close to zero as to be not worth talking about . The limiter is 2 x 1N4148 side by side rather than back to back as the diagram for two zener diodes . The low output is not a problem as the power amp can have the gain required . The . 57.5 dB is even more impressive as LM324 ( LM 358 dual package ) is not the stuff of dreams . The mains electricity is seldom better than -35 dB .

I made one error in building my oscillator . I used all 220K resistors . The one where the 10 M is shown should be lower than 220K . Useful to know that it still works as theory says it needs to be less . That is the place where adjustment is possible to trim frequency I suspect .

ESP - Sinewaves

I retested the motor . Note how at 245 V rms I get 12 V rms from what says is a 9 V transformer . 9V is at full load on 230 V . 51 R seems to be about right as a dropper .

I think using multiple 4.7 uF is a good choice as fine tuning is possible . Also a much better price . I noted excellent vibration using 10 uF . 20 uF gave more torque and more equal voltages , it also had more vibration . I suspect if using 20 uf the voltage could be dropped further . I have redrawn the transformer so as to stress that only a single winding is required . The voltage difference is typical of the LP12 ( 100 / 90 V Valhalla PSU )

4.7uf 250v 10% Metal. Poly Capacitor
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Old 8th March 2013, 07:43 PM   #70
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This is a real test of the circuit above at the motor as it rotates . The main thing to note is the wave is still noticeably a sine wave . The 3rd harmonic distortion is > 10 % . As disgusting as it looks it is the right side of OK . 3 rd harmonic is bad news because it works against the rotation , a prime source of vibration . The Garrard 501 was about - 55 db all distortion added together including the motor itself . If I had rewound the motor to 25 V rms I could have realized - 66 dB . 11 dB was the output transformer . The good news here is we don't need an output transformer if using a small power amp . 8 V rms is about the output of an op amp . L165 might be ideal ( TDA2030/40/50 also , same PCB I think should work )
Buy Operational Amplifiers Single power op-amp,L165V TO220-5b Magnatec L165V online from RS for next day delivery.
Buy Audio Amplifier Printed Circuit Boards TDA2030 PCB audioamplifier,10W 79x63.5mm One Way Circuits M12653 online from RS for next day delivery.

Last edited by nigel pearson; 8th March 2013 at 07:48 PM.
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