Hi Hiten,
A heavier platter will have a greater flywheel effect which will theoretically result in a smoother more speed stable rotation. Many manufacturers and diyers use heavy platters for this very reason, often adding extra weights near the periphery to increase the inertia still further.
A heavier platter will require a more substantial, larger bearing in order to support this greater mass. Larger and more heavily loaded bearings will dissipate more energy as friction as they rotate. Due to the limitations of manufacturing and materials all bearings will vary slightly in their energy dissipation as they rotate. This energy dissipation will vary more with a large bearing-heavy platter than with a small bearing-light platter. Very often a heavier platter will show worse speed stability than a lighter one for this reason.
The energy dissipated by the bearing is mainly in two forms, heat and vibration. Vibration will tend to manifest as rumble, larger bearings of a similar quality tend to rumble more. Hopefully the vast majority of the energy dissipated will be in the form of heat. This heat will warm up the bearing. As the bearing warms up different bits expand and the oil changes its viscosity both of which will effect the friction of the bearing. Until the bearing temperature has stabilised the friction will gradually change. Many decks don't sound their best until they have been playing for a long time. This problem tends to be worse with heavy platters.
So to answer your question. Having a heavier platter does not necessarily result in a better speed stability.
The mass of the platter will have no effect on the speed instability due to the compliance resonance of the arm which would appear to be one of the main sources of speed instability.
Niffy
Heavy platters have a potential downside, in that the spindle shaft might be more vulnerable to getting bent, particularly if the platter isn't removed for transport. It doesn't take much spindle bend or misalignment from vertical to induce once per platter pitch variation due to eccentricity..............
In hundreds of polar plots I've analysed over the years, I haven't noted a correlation between platter mass and pitch stability either way. As peeps have posted, other factors than platter rotational stability typically dominate IME.
LD
In hundreds of polar plots I've analysed over the years, I haven't noted a correlation between platter mass and pitch stability either way. As peeps have posted, other factors than platter rotational stability typically dominate IME.
LD
Heavy platter may reduce background noise. However, it is needed to be approved.
The ideal bearing is an air bearing. A roller air bearing can be loaded more than 100 lbs axially. A thrust air bushing has axial load 30 lbs. I tried roller air bearing but it was a failure due to lacking access to a precision machine shop. Air Force One table uses the whole platter as a integrated part of air bearing. So, it can support heavier platter under low air pressure. This is a perfect solution. Thin air film has damping factor, too. This why air bearing arms and turnables are quieter than regular ones. However, I think a platter which is heavier than 40 lbs is unnecessary. But it doesn't hurt either as long as the bearing can support the platter.
The ideal bearing is an air bearing. A roller air bearing can be loaded more than 100 lbs axially. A thrust air bushing has axial load 30 lbs. I tried roller air bearing but it was a failure due to lacking access to a precision machine shop. Air Force One table uses the whole platter as a integrated part of air bearing. So, it can support heavier platter under low air pressure. This is a perfect solution. Thin air film has damping factor, too. This why air bearing arms and turnables are quieter than regular ones. However, I think a platter which is heavier than 40 lbs is unnecessary. But it doesn't hurt either as long as the bearing can support the platter.
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Hi all,
As we've briefly discussed the effect of heavy platters on speed stability it is probably worth looking at a couple of other things that some manufacturers claim improve the speed stability of their decks. These are the use of a high torque motor and the use of multiple motors on belt drive decks.
I don't believe that there is any benefit to using a high torque motor. From Mr. Newton we have Torque = angular Acceleration x moment of Inertia. Increasing torque just means that you can accelerate the platter more quickly. This is exactly opposite to what you want which is to have a constant rotational speed, no acceleration. The amount of torque required is only enough to exactly overcome the friction of the bearing, the internal friction of the motor itself, hysteresis loss due to the flexing of the belt and stylus drag. The only time you might need more torque than this is when initially spinning the platter up to speed. I always spin my platter up to speed by hand anyway in order to minimize belt stretch so extra torque is not required. High torque motors tend to be larger and noisier, the only extra you get using a high torque motor is extra noise. If you use a motor right at its torque limit it may become more noisy so you do need to select a motor that is comfortable at the required torque.
If one low torque motor can supply enough torque to stably rotate the platter then all that using multiple motors can offer is more motor noise. Actually there is one benefit to using multiple motors. When using a single motor the belt tension creates a side thrust against the bearing sleeve. This side thrust can increase bearing friction and variations in that friction. If you use three motors equally spaced around the platter the tension of the belt no longer creates a side thrust against the sleeve of the decks main bearing. Exactly the same result can be achieved by using just a single motor and a pair of idler wheels. Just less motor noise.
I think the desire for more torque, more motors and more mass is largely the very human (male?) intuition that more is automatically better
Niffy
As we've briefly discussed the effect of heavy platters on speed stability it is probably worth looking at a couple of other things that some manufacturers claim improve the speed stability of their decks. These are the use of a high torque motor and the use of multiple motors on belt drive decks.
I don't believe that there is any benefit to using a high torque motor. From Mr. Newton we have Torque = angular Acceleration x moment of Inertia. Increasing torque just means that you can accelerate the platter more quickly. This is exactly opposite to what you want which is to have a constant rotational speed, no acceleration. The amount of torque required is only enough to exactly overcome the friction of the bearing, the internal friction of the motor itself, hysteresis loss due to the flexing of the belt and stylus drag. The only time you might need more torque than this is when initially spinning the platter up to speed. I always spin my platter up to speed by hand anyway in order to minimize belt stretch so extra torque is not required. High torque motors tend to be larger and noisier, the only extra you get using a high torque motor is extra noise. If you use a motor right at its torque limit it may become more noisy so you do need to select a motor that is comfortable at the required torque.
If one low torque motor can supply enough torque to stably rotate the platter then all that using multiple motors can offer is more motor noise. Actually there is one benefit to using multiple motors. When using a single motor the belt tension creates a side thrust against the bearing sleeve. This side thrust can increase bearing friction and variations in that friction. If you use three motors equally spaced around the platter the tension of the belt no longer creates a side thrust against the sleeve of the decks main bearing. Exactly the same result can be achieved by using just a single motor and a pair of idler wheels. Just less motor noise.
I think the desire for more torque, more motors and more mass is largely the very human (male?) intuition that more is automatically better
Niffy
Is there any reason to use two idler wheels instead of just one on the opposite side of the motor shaft?
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Hi benb,
The use of just one idler+motor will also cancel the belt tension. When using two idlers the belt tension helps to stabilize the platter equally in all directions, if using only one the platter is mainly stabilized only perpendicular to the line between motor and idler. Any number of idlers+motor symmetrically arrayed around the bearing will also work but two+motor is the simplest.
The bearing is made of two parts, the thrust pad/point that take the entire vertical load and the sleeve that keeps the bearing from tilting. Virtually all the friction and variations in friction of the bearing are due to the sleeve. If using an inverted bearing and two idlers+ motor the platter will naturally remain level. The sleeve can then be reduced as it will take absolutely no side force and in doing so it's contribution to friction and variations in that friction can also be reduced. By reducing the variations in friction speed stability can be improved. It is even possible to completely remove the sleeve in this configuration, the belt taking over the role of the sleeve.
Niffy
The use of just one idler+motor will also cancel the belt tension. When using two idlers the belt tension helps to stabilize the platter equally in all directions, if using only one the platter is mainly stabilized only perpendicular to the line between motor and idler. Any number of idlers+motor symmetrically arrayed around the bearing will also work but two+motor is the simplest.
The bearing is made of two parts, the thrust pad/point that take the entire vertical load and the sleeve that keeps the bearing from tilting. Virtually all the friction and variations in friction of the bearing are due to the sleeve. If using an inverted bearing and two idlers+ motor the platter will naturally remain level. The sleeve can then be reduced as it will take absolutely no side force and in doing so it's contribution to friction and variations in that friction can also be reduced. By reducing the variations in friction speed stability can be improved. It is even possible to completely remove the sleeve in this configuration, the belt taking over the role of the sleeve.
Niffy
I have the feeling that using multiple motors just causes them to come into alignment around their cogging profiles and increases cogging. At best they'll perfectly fight each others errors and give you a RMS reduction in speed instability, but we all know that's never going to happen.
Use a big platter, float it magnetically, use a weak, well compensated DC motor and controller with feedback control an enjoy.
Thick bearing oil, really thick, can also be a benefit in adding viscous drag to give a motor something to drive into (AC motors). If you have an adjustable speed controller it's one of the few compromise free improvements you can make to a deck.
Use a big platter, float it magnetically, use a weak, well compensated DC motor and controller with feedback control an enjoy.
Thick bearing oil, really thick, can also be a benefit in adding viscous drag to give a motor something to drive into (AC motors). If you have an adjustable speed controller it's one of the few compromise free improvements you can make to a deck.
High torque isn't useful per se, except when spinning up, as niffy already posted. In normal playback, even a high torque capable motor can't be operating at high torque if a platter is at constant speed, and if the spindle bearing has enough friction to require any significant torque to overcome, it has a fault.
The elephant in the room isn't torque, rather it's capacity for rate of change of torque. The capacity to overcome short term friction events, giving rise to changes in acceleration or 'jolt'.
But in a healthy bearing and platter arrangement, there shouldn't be significant short term variation in friction, nor significant 'jolt'.
And capacity for high rate of change of torque is a double-edge sword, because unwanted changes in motor torque, such as cogging , by definition, would be better transmitted. This is where belts come in to their own, by reducing capacity for rate of change of motor torque and thus providing isolation. But then what's the point of having a 'torque-responsive' motor, if it's isolated........?
Idler drive better couples rate of change of torque to the platter, at the price of also coupling motor noise, and as pointed out above, any benefit is to overcome a spindle bearing 'fault' that shouldn't be there in the first place....
So motor vibration-noise isolation is more important than torque or rate of change of torque capacity. In practice, one doesn't see effects of motor drive system in an otherwise healthy TT, based on 100s of polar plots. Faults, on the other hand, are fairly common and often undiagnosed.
If I had to pick a winner for speed stability it would be DD - not because of inherent advantage, but because there seem to be far fewer faulty DD TTs out there, IME. Healthy TTs can't be separated by drive type, other things being equal.
LD
The elephant in the room isn't torque, rather it's capacity for rate of change of torque. The capacity to overcome short term friction events, giving rise to changes in acceleration or 'jolt'.
But in a healthy bearing and platter arrangement, there shouldn't be significant short term variation in friction, nor significant 'jolt'.
And capacity for high rate of change of torque is a double-edge sword, because unwanted changes in motor torque, such as cogging , by definition, would be better transmitted. This is where belts come in to their own, by reducing capacity for rate of change of motor torque and thus providing isolation. But then what's the point of having a 'torque-responsive' motor, if it's isolated........?
Idler drive better couples rate of change of torque to the platter, at the price of also coupling motor noise, and as pointed out above, any benefit is to overcome a spindle bearing 'fault' that shouldn't be there in the first place....
So motor vibration-noise isolation is more important than torque or rate of change of torque capacity. In practice, one doesn't see effects of motor drive system in an otherwise healthy TT, based on 100s of polar plots. Faults, on the other hand, are fairly common and often undiagnosed.
If I had to pick a winner for speed stability it would be DD - not because of inherent advantage, but because there seem to be far fewer faulty DD TTs out there, IME. Healthy TTs can't be separated by drive type, other things being equal.
LD
Hello LD,
Please see following belt+Idler Design.
http://www.diyaudio.com/forums/analogue-source/174341-restoring-improving-thorens-td-124-mkii-259.html#post5353909
It decouples motor and belt being short and mostly being on idler and motor pulley; the slip, slack and stretch is avoided. This was posted couple of days before. But Honestly I didn't had changing torque advantage in my mind. I have few loose turntable induction motors if it is worth I should/can try it.
Regards
The Thorens thread is one I dip into every now and again though I haven't caught up with the last 50 pages or so. The Thorens TD124 is an old design and uses an induction motor rather than the more modern synchronous ac or dc motors. Induction motors require a significant load to work against in order to achieve speed stability. The Td124 uses a high friction bearing in order to load the motor. The bearing has to be very well set up and smooth running in order to achieve good speed stability. As well as the motor the rest of the drive train, belt and idler, has to be set up just right. When set up just right theTd124 is a good deck, not as good as a Garrard but available at a fraction the price.
Niffy
Niffy
I really don't think the 124 bearing can in any way be characterised as "high friction". The magnetic brake is what loads down the motor.
The 124 sounds very different and it is largely a question of musical preference when picking up a winner. It certainly does not have the momentum and bass slam of the Garrards but with classical and some jazz i definitely prefer it. It is also a "complete" solution, as the critical link main-bearing - tonearm is part of the design.
Actually i was not talking about TD-124 turntable.
Some random thoughts and questions.
- What are the disadvantages of a belt drive system ? I read belt slips, slacks and stretches. So A belt (Preferable round one) pressed between metal idler pulley and platter and of short length would be a good compromise. Isn't it ?
- Lets exaggerate things and say a platter weight is not distributed evenly one side is heavier. It would put uneven pressure on bearing. Will it affect speed stability ?
- I have read about inverted bearings and typical bearing which has resting point (Thrust pad) below the platter in horizontal plane. Would it be advantageous if this bearing point is neither inverted nor below but just in the same plane as the platter mass is. Would it make any difference regarding speed stability ?
Regards.
Some random thoughts and questions.
- What are the disadvantages of a belt drive system ? I read belt slips, slacks and stretches. So A belt (Preferable round one) pressed between metal idler pulley and platter and of short length would be a good compromise. Isn't it ?
- Lets exaggerate things and say a platter weight is not distributed evenly one side is heavier. It would put uneven pressure on bearing. Will it affect speed stability ?
- I have read about inverted bearings and typical bearing which has resting point (Thrust pad) below the platter in horizontal plane. Would it be advantageous if this bearing point is neither inverted nor below but just in the same plane as the platter mass is. Would it make any difference regarding speed stability ?
Regards.
Well I was thinking varying groove modulation/stylus friction in musical 'transients'. I think that could have an impact on/via:
- 'slippage' between record and platter/mat if not clamped firmly or sufficient spindle/record hole friction
- light platter/'just enough motor' designs, where the inertia is not enough to 'absorb' this change in modulation 'resistance'
Now this effect is not measured/exposed the normal polar plots , right? (based on constant signal/modulation). A locked grove constant signal pitch but transient modulation depth (step up/down response) might reveal something here (but not aware of tests/ test records providing exposure for such effects)
/wolf_skate
Arthur from pink triangle did a neat test to determine the effect of varying groove modulation on speed stability. He built a two arm deck. He placed a 12" test record on the platter then a 7" music record on top of this and firmly clamped the two to the platter. One arm could then play the test tone and the other the music. No variations in speed stability were discovered.
Niffy
Niffy
@Niffy OK you made me searching
some discussion
Those famous "needle-drag doesn't exist" tests - Vinyl Engine
and video(see at 3:10)
YouTube
shows ('static') stylus drag is there (compared to no needle in groove).. but then posts try to math-model the effect -> nearly no change in 'dynamic' drag = i.e. independent of modulation? (which I still can't really understand yet)
/wolf_skate
some discussion
Those famous "needle-drag doesn't exist" tests - Vinyl Engine
and video(see at 3:10)
YouTube
shows ('static') stylus drag is there (compared to no needle in groove).. but then posts try to math-model the effect -> nearly no change in 'dynamic' drag = i.e. independent of modulation? (which I still can't really understand yet)
/wolf_skate
Actually the technical name for this is jerk (seriously!).
Jerk (physics - Wikipedia)
Jolt is a soft drink I first saw in the 1980s, surely the first "energy drink" before the term was common or perhaps even coined, with various slogans along the lines of "all the sugar and twice the caffeine."
I've read the first half of the vinyl engine thread and the general consensus seems to be that the effect of stylus drag is way to small to effect speed stability. There were of course detractors who still instinctively believed that it has an effect.
With the YouTube video it is worth noting that it is an advertisement. They are selling a product. The product does exactly the same job as a strobe disk. My deck doesn't show any speed change stylus up to stylus down. I suggest that the demonstration deck has a poorly designed controller.
The changes in stylus drag due to groove modulation are however important for setting antiskate. But that's a topic for another thread.
Niffy
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