Spider27 Posted April 8, 2022 Posted April 8, 2022 I read on internet that 60Hz motor with 50Hz main supply reduce about 20% in speed. However, when I tested with Hurst 3001-001 motor which is 115v 60Hz motor on my AR XA turntable using Tortech stepdown transformer (240v to 110v) with correct sized pulley, the speed achieved is 33.0 rpm against 33.3 rpm and 44.8 rpm against target 45.0 rpm which means that 0.9% reduction on 33.3 rpm and 0.4% reduction on 45 rpm which is less than 1% for both which is quite accurate and I do not understand why it is. Does step down transformer change the frequency from 60Hz to 50Hz when dropping the voltage which I doubt it does? And, original cap that motor came with is 0.25 uf MKP cap and does it help increasing the cap value a bit more to achieve extra 0.4~0.9% boost in speed of the motor to achieve close to target speed (33.3 and 45 rpm)?
andyr Posted April 8, 2022 Posted April 8, 2022 (edited) 8 hours ago, Spider27 said: I read on internet that 60Hz motor with 50Hz main supply reduce about 20% in speed. However, when I tested with Hurst 3001-001 motor which is 115v 60Hz motor on my AR XA turntable using Tortech stepdown transformer (240v to 110v) with correct sized pulley, the speed achieved is 33.0 rpm against 33.3 rpm and 44.8 rpm against target 45.0 rpm which means that 0.9% reduction on 33.3 rpm and 0.4% reduction on 45 rpm which is less than 1% for both which is quite accurate and I do not understand why it is. As the rotational speed of an AC motor depends on the AC frequency being fed to it ... I also would've thought that feeding a 60Hz motor with 50Hz would result in a 20% reduction in rotational speed. (Actually 50 / 60 = about 17%.) I would suggest your AR TT has a different-sized pulley fitted to the Hurst motor, which is appropriate for a 50Hz mains feed. The pulley is not machined precisely accurately - hence you are getting slightly "off" speeds; what you need is a motor speed controller that allows you to change the frequency being output, slightly. 8 hours ago, Spider27 said: Does a step down transformer change the frequency from 60Hz to 50Hz when dropping the voltage which I doubt it does? No it certainly doesn't. 8 hours ago, Spider27 said: And, original cap that motor came with is 0.25 uf MKP cap and does it help increasing the cap value a bit more to achieve extra 0.4~0.9% boost in speed of the motor to achieve close to target speed (33.3 and 45 rpm)? Changing the value of the cap does not affect the rotational speed of the motor - only changing the AC frequency does this. Andy Edited April 8, 2022 by andyr 1
MLXXX Posted April 8, 2022 Posted April 8, 2022 9 hours ago, Spider27 said: And, original cap that motor came with is 0.25 uf MKP cap and does it help increasing the cap value a bit more to achieve extra 0.4~0.9% boost in speed of the motor to achieve close to target speed (33.3 and 45 rpm)? No, as andyr has mentioned above. The Hurst 3001-001 is indeed a synchronous motor. It will be synchronous in its rotational speed with the prevailing frequency of the mains supply it is being powered by. Changing the capacitor value would not change the speed. I note that the difference in pitch created by a rotating a disc at 33.0rpm instead of 33.33rpm is a lowering by about 0.16 semitones. As a comparison, watching a PAL DVD of a movie, a 24 frames per second movie plays at 25 frames per second, typically resulting in an increase in pitch of about 0.71 semitones. 1
Spider27 Posted April 8, 2022 Author Posted April 8, 2022 Thank you so much. Understood that cap value does not change the speed but frequency of main supply does. I was told that the pulley is designed for 50Hz hence the speed accuracy is fairly close to the target speed. How about sanding the sub-platter slightly with very fine sandpaper like 1000 or 2000 grit or make the rubber belt a bit tighter to increase the speed a bit?
andyr Posted April 8, 2022 Posted April 8, 2022 7 hours ago, Spider27 said: I was told that the pulley is designed for 50Hz hence the speed accuracy is fairly close to the target speed. Aha! (As I suggested. ) 7 hours ago, Spider27 said: How about sanding the sub-platter slightly with very fine sandpaper like 1000 or 2000 grit or make the rubber belt a bit tighter to increase the speed a bit? Making the belt tighter won't change the speed. The speed results from the ratio of pulley diam to sub-platter diam. Sanding the sub-platter will slow the speed ... you want it slightly faster, right? To be able to achieve the tiny increases you are looking for ... requires a motor speed controller that allows you to change the AC frequency being fed to the motor, slightly. Andy 1
Spider27 Posted April 8, 2022 Author Posted April 8, 2022 30 minutes ago, andyr said: Sanding the sub-platter will slow the speed ... you want it slightly faster, right? I thought that pulley diameter gets bigger, it gets more turn so faster. On the other hand, subplatter diameter gets smaller, it gets more turn so faster like bicycle gear.
Warren Jones Posted April 8, 2022 Posted April 8, 2022 (edited) Keep in mind that mains frequency is not exact and will vary +/- 0.15Hz from nominal 50Hz. Then you have the error inherent in the device you are measuring the rotational speed with. These errors are cumulative. As Andy said the only way to vary the speed of a synchronous motor is to vary the Frequency, Linn and others do this with a motor controller that generates frequency from a precision clock, but even this will have errors and will never be exact. The capacitor on the motor is there to change the PHASE between the 2 windings, if this cap is not the correct value for the windings and drive frequency the motor will not start and run. Tightening the belt could cause other negative effects like putting too much side thrust on the platter and motor spindles. It will also change the resonant frequency of the belt altering the the vibration profile to the platter. I would NOT recommend sanding the subplatter if you don"t get the profile correct the TT will throw belts, and if the surface is not true W&F will increase. Edited April 8, 2022 by Warren Jones 2
aussievintage Posted April 9, 2022 Posted April 9, 2022 13 hours ago, MLXXX said: I note that the difference in pitch created by a rotating a disc at 33.0rpm instead of 33.33rpm is a lowering by about 0.16 semitones. As a comparison, watching a PAL DVD of a movie, a 24 frames per second movie plays at 25 frames per second, typically resulting in an increase in pitch of about 0.71 semitones. One way to fix a speed problem like this, is to throw away all strobes, and speed measuring devices. 2 2
rocky500 Posted April 9, 2022 Posted April 9, 2022 Someone with access to a 3D printer could make a few pullies in different sizes. Once you have the exact size you need you could get someone to machine one to the exact size?
wartman Posted April 9, 2022 Posted April 9, 2022 Try a few different belt thicknesses. Makes a huge difference on some turntables,, especially some Yamaha ones.. I've had lots of TT's come through with similar issues. 1
Spider27 Posted April 9, 2022 Author Posted April 9, 2022 5 minutes ago, wartman said: Try a few different belt thicknesses. Makes a huge difference on some turntables,, especially some Yamaha ones.. I've had lots of TT's come through with similar issues. That is very interesting. I wasn’t aware that belt thickness makes difference. I will look out for different thickness belts to try. is thinner makes faster in speed in general?
wartman Posted April 9, 2022 Posted April 9, 2022 I'll have to check my notes through the week. Off memory, thicker speeds them up a bit. 1
wartman Posted April 9, 2022 Posted April 9, 2022 Example of belt difference. Yamaha yp-500 TT 0.6mm thickness is perfect. 0.9mm thickness is way too fast. 1
Spider27 Posted April 9, 2022 Author Posted April 9, 2022 1 minute ago, wartman said: Example of belt difference. Yamaha yp-500 TT 0.6mm thickness is perfect. 0.9mm thickness is way too fast. Thank you for sharing. I guess that the reason for the difference is that thicker the belt will help achieving more torque and less slippery hence the faster speed?
wartman Posted April 9, 2022 Posted April 9, 2022 I have read up on this subject, unfortunately I can't remember why the thickness matters. Might be time to research this again, so I can forget it again. The problem with ever diminishing grey matter..... 1
Spider27 Posted April 9, 2022 Author Posted April 9, 2022 I just found a belt which is actually 1 cm shorter in diameter so tension is a bit more and tested it with and speed is exactly same. In my test, the tension of belt does not make a difference. I will report back with thicker belt if I can find one to test with.
Spider27 Posted April 9, 2022 Author Posted April 9, 2022 I am currently using stepdown transformer but eventually will use a resistor to reduce the voltage down to 115v like Thorens, Ariston turntables do. Does the voltage drop resistor value makes difference in terms of motor speed?
Gandra Posted April 9, 2022 Posted April 9, 2022 (edited) I recently had a controller built for my Garrard. Different T'table altogether but same issues nonetheless. Since I started measuring frequency more carefully now, or actually started paying attention to its accuracy, the main thing I found was that it varies wildly! Not only do I need to adjust it at the beginning of a listening session but every hour or so as well. This is the anal solution - a more practical one as someone above alluded to is to simply ignore it and hopefully you won't notice the difference. Just enjoy the music and the crazy hifi ride. Edited April 9, 2022 by Gandra 1 1
aussievintage Posted April 9, 2022 Posted April 9, 2022 3 hours ago, wartman said: I have read up on this subject, unfortunately I can't remember why the thickness matters. Because the effective pulley diameter is about halfway through the belt thickness. Make the belt thicker, the effective pulley size increases. 2
wartman Posted April 9, 2022 Posted April 9, 2022 2 minutes ago, aussievintage said: Because the effective pulley diameter is about halfway through the belt thickness. Make the belt thicker, the effective pulley size increases. Ahhh,, that's right.. Thanks, I don't need to look it up now. 1
Spider27 Posted April 9, 2022 Author Posted April 9, 2022 The belt that I currently have is used one. It looks still good but I just ordered brand new one and hopefully it helps increasing the speed a bit. I will report back the outcome for others' interest and reference.
Spider27 Posted April 9, 2022 Author Posted April 9, 2022 1 hour ago, Gandra said: I recently had a controller built for my Garrard. Different T'table altogether but same issues nonetheless. Since I started measuring frequency more carefully now, or actually started paying attention to its accuracy, the main thing I found was that it varies wildly! Not only do I need to adjust it at the beginning of a listening session but every hour or so as well. This is the anal solution - a more practical one as someone above alluded to is to simply ignore it and hopefully you won't notice the difference. Just enjoy the music and the crazy hifi ride. Thank you for sharing. I think that one option to keep the speed accurate all the time without manual adjustment is somehow combining tachometer with speed controller so tachometer constantly monitoring the speed and adjust frequency automatically.
andyr Posted April 9, 2022 Posted April 9, 2022 7 minutes ago, Spider27 said: Thank you for sharing. I think that one option to keep the speed accurate all the time without manual adjustment is somehow combining tachometer with speed controller so tachometer constantly monitoring the speed and adjust frequency automatically. Not quite, S! With a DC motor (whose speed depends on the voltage fed to it), you have to continually monitor and adjust ... to keep the DC motor at the correct rotational speed. But as an AC motor's speed depends solely on the AC frequency fed to it ... once the appropriately-generated AC frequency has been set - you don't need to adjust it 'on the fly'. Andy 1
Spider27 Posted April 10, 2022 Author Posted April 10, 2022 Is there any formula to calculate the required value of resistor to reduce the voltage down from main supply 230v to 115v motor? If I understood correctly, Thorens use 5.6K resistor, Ariston uses 10K resistor, Rega uses 12K resistor. I am thinking to use 10 or 12K resistor for dropping voltage. Is this correct value?
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