For Turntables it is said all drive systems are good if well implemented. Some basic disadvantages of idler is direct connection to motor pulley and for belts it sometimes slips, and due to cogging and probably other influences. it stretches and slacks. This may affect speed stability. Here is a good compromise which decreases these effects.
Please see picture attached. I have used a round belt on metal pulley driven by Motor. The metal idler is pressed inside the platter rim which driven by isolated motor. Due to belt being short and pressed between rim and metal idler some advantages may be gained from this implementation with regards to problems mentioned.
Do post other turntable mods.
Regards.
Please see picture attached. I have used a round belt on metal pulley driven by Motor. The metal idler is pressed inside the platter rim which driven by isolated motor. Due to belt being short and pressed between rim and metal idler some advantages may be gained from this implementation with regards to problems mentioned.
Do post other turntable mods.
Regards.
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I remember taking apart an OLD garrard table once, an rc80 I believe, that had something similar. The motor pully connected to a belt with teeth which had a small diameter. The other end of the belt went around a cog that the idler wheel was attached to, thus it eliminated any issues with motor/idler interface.
The motor would spin the attached cog, turn the belt, which turned a cog attached to the rod holding the idler wheel
The motor would spin the attached cog, turn the belt, which turned a cog attached to the rod holding the idler wheel
From what I read the only disadvantages of Belt drives is slips and stretching.
Since Round belt is pressed between metal idler and platter rim, wouldn't it have some what lower belt slips and stretching ?
Other way would be to have the Idlers pressing rim in the center of the belt where slips and stretches would be maximum. Think of it as having a constant tension on the belt.
Regards.
Since Round belt is pressed between metal idler and platter rim, wouldn't it have some what lower belt slips and stretching ?
Other way would be to have the Idlers pressing rim in the center of the belt where slips and stretches would be maximum. Think of it as having a constant tension on the belt.
Regards.
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Thanks gigigirl. I crossposted when you were typing. Please read my above post. This way we isolate motor from rim. and some what have direct coupling of drive system.
Regards.
With a motor for an idler drive table, any lateral force on the motor spindle is going to be of no consequence.....same for a belt drive system. You are talking about a fraction of a milimeter between the motor spindle and the oilite bearing. At the bottom of the motor is another oilite bearing and a thrust plate. Not an issue. Lateral force is seriously minimized.
If you are talking about the platter bearing, those tolerances are very tight as well. Be more concerned with the smoothness of the ball bearing that the bottom of the platter between the platter and thrust plate.
If you are talking about the platter bearing, those tolerances are very tight as well. Be more concerned with the smoothness of the ball bearing that the bottom of the platter between the platter and thrust plate.
I have observed that swapping the bottom and the top cup and ball bearings, in addition to flipping the thrust bearing plate, in old Dual idler drive TT's, especially in those big 1219's and 1229's with their round shaped, powerful motors, helps reducing vibrations significantly. I deduce this to increase of clearance in the top bearings, most probably due to the lateral force the idler wheel applies to the pulley.
Btw, I'm speaking of more than 40 years of lifetime here
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Best regards!
Btw, I'm speaking of more than 40 years of lifetime here
.Best regards!
Thanks gentlemen for your thoughts. And thanks for tolerating me.
As Kay has said the bearing well made should last decades. Current bearing are already good. But how about a tapered spindle and bush bearing. Advantage being it will have tightest tolerance one can get. What are the shortcomings of such bearings ? I can only imagine the friction will rise so after making tapering bush we can give a little offset (extremely tiny cut) in the middle. Should this work ?
Regards
As Kay has said the bearing well made should last decades. Current bearing are already good. But how about a tapered spindle and bush bearing. Advantage being it will have tightest tolerance one can get. What are the shortcomings of such bearings ? I can only imagine the friction will rise so after making tapering bush we can give a little offset (extremely tiny cut) in the middle. Should this work ?
Regards
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One option with the conical bearing is to fit a ball and thrust plate at the bottom, the thrust plate being adjustable by means of a fine threaded bolt. this would allow a very small amount of clearance.
There is however still the matter of uneven wear between the surfaces, which would eventually cause them to no longer be parallel and therefore tend to bind on the area where there is less wear if an adjustment was made to try to reduce the clearance of the worn area.
There is however still the matter of uneven wear between the surfaces, which would eventually cause them to no longer be parallel and therefore tend to bind on the area where there is less wear if an adjustment was made to try to reduce the clearance of the worn area.
ahh ! OK Kay I got that. As bearing wears it settles down and probably will seize.
Ralphs idea of thrust bearing is good. Or after making tapered spindle we can make spiral grooves (not my idea, it has been posted before) to lower the contact area and move the lubricant and magnets of enough strength at bottom to reduce pressure/lift the platter (Like Verdier) should also work I guess.
Confession : I understand the best design/implementation are already done. The work done over the decades by people is appreciated and wisdom respected. I am just sharing different thoughts to learn.
Regards.
Ralphs idea of thrust bearing is good. Or after making tapered spindle we can make spiral grooves (not my idea, it has been posted before) to lower the contact area and move the lubricant and magnets of enough strength at bottom to reduce pressure/lift the platter (Like Verdier) should also work I guess.
Confession : I understand the best design/implementation are already done. The work done over the decades by people is appreciated and wisdom respected. I am just sharing different thoughts to learn.
Regards.
Vertical Idler drive Mod : Without taking anything away from well improved Lenco and due respect to it, I was thinking would the following be of any improvement ?
In vertical idler drive turntables the idler contacts the flat surface of the platter to drive it and it moves along the diameter to change speed. So basically this is a tangent (Idler) rotating circle (Platter). The rubber idler presses against the platter so contact area is comparatively large (On horizontal idler drive this would not have been a problem). So we have a tangent (Idler) rotating the circle. This may cause variations as idler tries to keep in sync. with rotating circle. (Flutter ?) Also all moving parts need minor clearance to run. One being idler and other being mechanism to move idler across to change speed. This may also contribute to varying speed.
So smallest contact area of idler-platter surface and fixed ridge would be beneficial I suppose. As shown in the pic. a circular metal ridge with rounded tip is used on which a sufficiently wide rubber idler pushes. The circumference of idler and roundness of ridge is in 90 degrees to each other. This presents lowest contact area and besides even if idler moves/vibrates somewhat due to moving parts i.e. idler and speed change mechanism, the ridge being fixed the minor fluctuations/vibrations will not affect speed stability.
Things like speed change etc. can be arranged by other means.
Regards
In vertical idler drive turntables the idler contacts the flat surface of the platter to drive it and it moves along the diameter to change speed. So basically this is a tangent (Idler) rotating circle (Platter). The rubber idler presses against the platter so contact area is comparatively large (On horizontal idler drive this would not have been a problem). So we have a tangent (Idler) rotating the circle. This may cause variations as idler tries to keep in sync. with rotating circle. (Flutter ?) Also all moving parts need minor clearance to run. One being idler and other being mechanism to move idler across to change speed. This may also contribute to varying speed.
So smallest contact area of idler-platter surface and fixed ridge would be beneficial I suppose. As shown in the pic. a circular metal ridge with rounded tip is used on which a sufficiently wide rubber idler pushes. The circumference of idler and roundness of ridge is in 90 degrees to each other. This presents lowest contact area and besides even if idler moves/vibrates somewhat due to moving parts i.e. idler and speed change mechanism, the ridge being fixed the minor fluctuations/vibrations will not affect speed stability.
Things like speed change etc. can be arranged by other means.
Regards
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Why not use a sub platter like the garrard ap75/76 , its well established and further proven with stacked platter lenco's , adding a clean power supply to smooth the motor also is beneficial, again proven on lenco heaven site , thorens and braun used tensioned belt idler drive systems to overcome motor Born parasitics so it would be best to address the problem directly rather than add more complexity and possible problems I feel the best approach would be an idler driven sub platter ,driven in turn by a high quality dc servo controlled motor with mechanical impedance mismatched platter made of POM or similar . Just a thought
Hi Hiten,
Actually, the very compliant connection between the motor and platter is a huge benefit. What you are trying to achieve is a heavy rotating platter system that is isolated from the outside world. Minor variations due to cogging " or any other cause should be averaged out but the coupling between platter and motor. Also, during the initial spin-up to playing speed, the motor and coupling system are under great stress. To reduce this, Thorens uses a felt clutch that allows the motor to spin at it's rated speed without having the bear the inertial moment of the heavy platter. So the tension on the belt is maintained at some lower value than it would otherwise be in. You can do this with other motors by supplying a weak drive that would allow the motor to spin up gradually. So there is a reason for the small motors on all of the top turntables.
In the past, the idler drive turntables were used mostly in radio stations where spin-up time was critical. Turntables were advertised as to how quickly they could get up to speed. That's why the Thorens TD-124 has a sub platter. The top platter drops onto the already turning main platter and is forced to rotation speed by the rubber "spacers"on the main platter. Of course, a large, powerful motor was also required. The W&F specs on these tables were not nearly as good as what is normal for an idler wheel drive turntable. Why? Tight coupling between the motor and platter (flywheel) connects every vibration from the drive system to the record pretty well.
I used to have idler drive turntables. Once I discovered the belt drive with very heavy platters the search was over. Now I am most concerned with the quality of the bearings. They are the only source of noise (rumble) and speed instability left. The coupling only needs to supply lost energy due to windage, bearing friction and stylus friction. The same principles apply to direct drive turntables. Weak coupling between the motor and platter gives superior results. And the mean speed of the platter? There is feedback between the platter and motor system. For my Thorens TD-125 MKII and TD-126 MKII, I am the corrective feedback. Most direct drive tables use feedback directly from the platter compared to a crystal oscillator for correction.
Anyway, the last thing you want is tight coupling between the motor and platter ... unless you are a DJ and need the platter to come up to speed in 1/3 a revolution or better.
-Chris
Actually, the very compliant connection between the motor and platter is a huge benefit. What you are trying to achieve is a heavy rotating platter system that is isolated from the outside world. Minor variations due to cogging " or any other cause should be averaged out but the coupling between platter and motor. Also, during the initial spin-up to playing speed, the motor and coupling system are under great stress. To reduce this, Thorens uses a felt clutch that allows the motor to spin at it's rated speed without having the bear the inertial moment of the heavy platter. So the tension on the belt is maintained at some lower value than it would otherwise be in. You can do this with other motors by supplying a weak drive that would allow the motor to spin up gradually. So there is a reason for the small motors on all of the top turntables.
In the past, the idler drive turntables were used mostly in radio stations where spin-up time was critical. Turntables were advertised as to how quickly they could get up to speed. That's why the Thorens TD-124 has a sub platter. The top platter drops onto the already turning main platter and is forced to rotation speed by the rubber "spacers"on the main platter. Of course, a large, powerful motor was also required. The W&F specs on these tables were not nearly as good as what is normal for an idler wheel drive turntable. Why? Tight coupling between the motor and platter (flywheel) connects every vibration from the drive system to the record pretty well.
I used to have idler drive turntables. Once I discovered the belt drive with very heavy platters the search was over. Now I am most concerned with the quality of the bearings. They are the only source of noise (rumble) and speed instability left. The coupling only needs to supply lost energy due to windage, bearing friction and stylus friction. The same principles apply to direct drive turntables. Weak coupling between the motor and platter gives superior results. And the mean speed of the platter? There is feedback between the platter and motor system. For my Thorens TD-125 MKII and TD-126 MKII, I am the corrective feedback. Most direct drive tables use feedback directly from the platter compared to a crystal oscillator for correction.
Anyway, the last thing you want is tight coupling between the motor and platter ... unless you are a DJ and need the platter to come up to speed in 1/3 a revolution or better.
-Chris
Thanks Chris.
As said in earlier post; the performance for turntables are already achieved by people long way back. vintage turntables like Lencos, Garrards and Thorens idlers have good following. So posted some thoughts. Belt drive can easily achieve the specific targets and require even less maintenance then idlers.
I also understand what you are saying about belt drives. Belt drives are easiest way to achieve the desired results. However I read in various forums about belt creeping, stretching and slacking problems. So posted some ideas. Do give your assessment on quasi belt drive which I posted in #1 post. I think it will have multiple benefits. That is of creeping, stretching and slacking etc.
Regards.
As said in earlier post; the performance for turntables are already achieved by people long way back. vintage turntables like Lencos, Garrards and Thorens idlers have good following. So posted some thoughts. Belt drive can easily achieve the specific targets and require even less maintenance then idlers.
I also understand what you are saying about belt drives. Belt drives are easiest way to achieve the desired results. However I read in various forums about belt creeping, stretching and slacking problems. So posted some ideas. Do give your assessment on quasi belt drive which I posted in #1 post. I think it will have multiple benefits. That is of creeping, stretching and slacking etc.
Regards.
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