Hmmm, ok, thanks for that info Mark. So it would seem then that a turntable would naturally fight the centre point of spindle contact and depending on the spindle/bearing-sleeve construction/fit, the points where the spindle contacts the upper and lower lips or rims of the bearing sleeve could be of great influence to the quality of smoothness of rotation of the platter (due to the rotational nature of precession). So attention must be paid to the quality of bearing fit and/or any presence of play or wobble in the bearing system and not just to the quality of the spindle contact point?
Or am I messing this up?
Or am I messing this up?
I think it's best to try to visualise the rotation and precession at the same time.
Look at the top in this link. It's spinning too fast for the video camera to show the spin but you can clearly see the precession - in this case it's because the axis of the top is slightly tilted so gravity is providing the tipping torque.
Now imagine your platter / spindle doing the same thing at about the same ratio of speeds. If you imagine how the spindle rubs against its housing, you should be able to see the contact patches on the housing rotating slowly in the same direction but 180 degrees apart.
If one of these contact patches is roughly in the plane of the side force from the belt / idler pully / whatever and another of them is placed some distance vertically from there and the tolerances are such that the degree of precessive motion is small (which requires that the bearing is stiff enough to resist the precessive force) it doesn't really matter where the vertical support is, it's not playing this game.
The point of all this is that there's more going on than the obvious.
Look at the top in this link. It's spinning too fast for the video camera to show the spin but you can clearly see the precession - in this case it's because the axis of the top is slightly tilted so gravity is providing the tipping torque.
Now imagine your platter / spindle doing the same thing at about the same ratio of speeds. If you imagine how the spindle rubs against its housing, you should be able to see the contact patches on the housing rotating slowly in the same direction but 180 degrees apart.
If one of these contact patches is roughly in the plane of the side force from the belt / idler pully / whatever and another of them is placed some distance vertically from there and the tolerances are such that the degree of precessive motion is small (which requires that the bearing is stiff enough to resist the precessive force) it doesn't really matter where the vertical support is, it's not playing this game.
The point of all this is that there's more going on than the obvious.
Mark, what bearing factors or design considerations would you think are paramount in dealing with precession? Would it be the tolerances of the spindle to bearing fit or would it be construction details of the bearing housing? I know that the Linn LP12 Cirkus upgrade kit includes a bearing housing with larger/stronger bearing mounting flange as an important part of the upgrade kit. And if I am not mistaken, the Linn spindle has some taper to it, from a web article:
(Link to Article)
Soundbound
(Link to Article)
Soundbound
what i got in from them for about same not including shipping...i designed the 2.5 inch platter and bearing assembly...polished pic available of platter and bearing on Choir Audio diy web sight http://www.choiraudio.com/IMG_5696.JPG
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Here's a nice platter.
Classic Aluminum Platter Bearing [Table Parts:T-1014] - $800.00 : VPI Industries Inc.
Classic Aluminum Platter Bearing [Table Parts:T-1014] - $800.00 : VPI Industries Inc.
I purchased two green flywheel papst motors from ebay for possible use in a diy turnt
I've looked at this for quite a while now, and have even designed a complete turntable suitable as a belt, rim or idler drive. The motor system could be either AC or DC.
There are pluses and minuses to everything, but each type of motor system can have their own issues. I agree that the Mark Kelly/Sylvain Bergeron DC controller PCB makes a lot of sense if DC is what you are after. I think there is the ability to compensate for increased temperature and load. I'll have to re-read the documentation.
For AC synchronous speed controls the issue is getting to the correct frequency to drive the motor at the correct speed. This entails the use of high precision oscillator (thankfully readily available), some sort of filter to keep noise to a minimum, and the inclusion of an amplifier circuit to get to an appropriate voltage AND/OR the use of a phasing capacitor . If using only a phasing capacitor you rely on the AC mains frequency (and hope the frequency of your mains is dead on 50Hz or 60Hz, whatever the case may be). So initially the AC motor/capacitor system can get you started.
The phasing capacitors for a particular speed to be maintained are motor specific (well more correctly the number of poles) and are usually provided by the motor manufacturers. Also you must determine the AC voltage you want to run at. For example Hurst (and I am not neccessarily recommending them) has a 24VAC and a 115 VAC motor that is essentially identical, but require different phasing capacitor. AFAIK dropping the voltage increases torque so there is some appeal to that option. But a much larger capacitor (or group of capacitors) is required and are not included with the 24 VAC version motor.
Regardless of which motor type and what the designed RPM for the motor is, drive pulleys are required (or spindle extensions, etc) and some means of either altering the frequency (for AC drives) and/or the voltage required (mainly for DC types, but altering the voltage for AC motors can get you to a "sweet spot" where mechanical noise is reduced to a minimum, while still maintaining the ability to drive the platter as per the requirements for a Premotec motor as used in the Linn LP12.
This is not meant to create an new thread, there are enough here and various other sites that discuss/argue the merits of AC vs DC motors and their use in turntables.
Hope this helps and doesn't add to the confusion...[I purchased two green flywheel papst motors from ebay for possible use in a diy turntable project. I know nothing of them and got little info from the seller but the price was right...highest bidder at 16.50 cdn...I am looking to get a power supply/speed control for them...I will try to attach pics for these (original from ebay)...Motor numbers are as follows: KLO 14.50-2-420D followed by a triangle symbol...second line reads as follows: 7cha Nr 7882-064...what type of motor is this AC or DC?..could these possibly be 3 phase?...no indicaton of voltage, frequency etc...any info or help would be appreciated.
Attached Thumbnails/QUOTE]
2 green Pabst motors.
Stuartarm : any information? The platter and bearing look pretty nice (better than anything I could manage). I imagine a massive deck. If you have the ebay posting number (whether completed or not) then a link would get us there
To me this is almost a false economy (in design not financial). I understand the desire for a large heavy platter, but the need for one can easily be minimized or disregarded if multiple motors are used.Personally any platter in the 7-12 lbs. range should suffice if the drive system, bearing and materials are upto the task.
If a heavy-"ish" platter is to be used then geometry of the platter needs to be addressed (this is a subject that many folks don't consider). The shape can be as important (or even more so) as the mass of the platter.
Stuartarm : any information? The platter and bearing look pretty nice (better than anything I could manage). I imagine a massive deck. If you have the ebay posting number (whether completed or not) then a link would get us there
To me this is almost a false economy (in design not financial). I understand the desire for a large heavy platter, but the need for one can easily be minimized or disregarded if multiple motors are used.Personally any platter in the 7-12 lbs. range should suffice if the drive system, bearing and materials are upto the task.
If a heavy-"ish" platter is to be used then geometry of the platter needs to be addressed (this is a subject that many folks don't consider). The shape can be as important (or even more so) as the mass of the platter.
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...not actually sure what you mean nanook...this platter is only 1/2 inch thicker than many high end platters out there...yes i agree there is more to designing turntable platters than size...bearing set up is also crucial and if you look at finished product on the bearing it could easily do without a plinth its so massive...but will do one anyway when i get the foot design absolutely right...regardless i am not going to stop until this is perfected being it overkill or not it is what i desire...this project is the biggest i have ever embracedStuartarm : any information? The platter and bearing look pretty nice (better than anything I could manage). I imagine a massive deck. If you have the ebay posting number (whether completed or not) then a link would get us there
To me this is almost a false economy (in design not financial). I understand the desire for a large heavy platter, but the need for one can easily be minimized or disregarded if multiple motors are used.Personally any platter in the 7-12 lbs. range should suffice if the drive system, bearing and materials are upto the task.
If a heavy-"ish" platter is to be used then geometry of the platter needs to be addressed (this is a subject that many folks don't consider). The shape can be as important (or even more so) as the mass of the platter.
was a custom build bearing and platter assembly i designed so it was double their own platter...1200 cdn delivered...just so u know they also use same bearing concept after my submitted design to sell an upgraded platter for rega turntables..Choir Audio
Stuartarm : any information? The platter and bearing look pretty nice (better than anything I could manage). I imagine a massive deck. If you have the ebay posting number (whether completed or not) then a link would get us there
To me this is almost a false economy (in design not financial). I understand the desire for a large heavy platter, but the need for one can easily be minimized or disregarded if multiple motors are used.Personally any platter in the 7-12 lbs. range should suffice if the drive system, bearing and materials are upto the task.
If a heavy-"ish" platter is to be used then geometry of the platter needs to be addressed (this is a subject that many folks don't consider). The shape can be as important (or even more so) as the mass of the platter.
7lbs is fine . The Garrard 401 is a good example of design . The motor is more powerful than average ( using about 24VA ) . The drive coupling is more ridged via the idler drive . The motor is a hysteresis type which shows no pole jumps if rotated by hand . The bearing length is about twice that of many and thicker . The rumble from the bearing alone is better than - 80 dB weighted .
I had a bronze platter made for a 301 . The sound was ponderous . Eventually it was scooped out and worked well .
The best improvement to a 301/401 was a very low distortion power supply .
stuartarm: 1/2" thickness increase for a solid platter is a huge amount of mass being added. I didn't see the underside of the platter, but am assuming it is a solid disk of material. If not machined out, then a lot of energy is wasted and contributes little to the flywheel effect vs energy applied.There are a couple of ways to get to the same result. Multiple motors vs. massive platter is one. The key is to conserve momentum.
Feet have been designed in so many iterations that somewhere feet must exist. If wanting to do something strictly custom because you can, that's OK. However unless you have some fairly sophisticated measuring equipment it is unlikely you will improve on existing designs.
I look forward to seeing the end result.
If you use a very elastic belt a low distortion power supply will be of little importance . Some now use linen or tape recorder leader as a connection . If so a quality once described as dynamic wow is reduced . This is probably caused by the varying load on the stylus point . Secondary effect is vibration through the structure which is much over estimated . If the motor is of the typical synchronous/stepper/DC type ( notched ) then the usefulness of a low distortion supply is less . From that it is critical to infer that the motor is very important .
The Birth of the Garrard 501
If you take the direct coupled system of a Garrard it resembles the Bumble bee . The Bumble bee should not be able to fly . Equally the Garrard should be an impossible concept . Certainly cheaper turntables can out do it's OK rumble figures ( - 57 dB typical ) . The first thing noticed using a low distortion power supply is that the motor has less vibration . Guess what , the rumble figures are now - 79 dB ( that's where I got after 15 years with the Garrard 501 ) . What will surprise most people is very little of the 401 was changed . I retained the platter mass .
My point is this . The ARX turntable was developed to make a cheap transcription turntable possible . It is not an ideal starting point . I would say it is a near perfect example of what it set out to do . The Garrard 301/401 , Technics SP10 and to a lesser extent Thorens TD124 were the true transcription turntables . They are difficult to clone .
If I were building a high grade turntable from scratch I would use the Technics 1210 motor run at high speed . It would have the stiffest connection I could get . The platter and bearings I see used here seem fine . It has no need for a special power supply . People do play with how it's servos work . The flywheel concept of turntables is baffling . It should be critical , it seems merely helpful . On the other hand bearing design ( not quality so much as long as it is fit for purpose ) is totally critical .
More reading if not already seen .
BELT DRIVE TURNTABLE Philips Thorens Verdier Melco Micro Mercure NOTES DIY
BELT DRIVE TURNTABLE Philips Thorens Verdier Melco Micro Mercure NOTES DIY
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