As said in earlier post I have experimented with magnetic bearings on an idlerdrive.
Graeme UK: First why using a magnetic bearing? To me because a magnetic bearing is more quiet than a inverted one. Less resistance (if there is less) makes no sense, at least not for an idlerdrive.
Mine idlerdrive isn’t that quiet, maybe yours is. A simple experiment to test it. Choose a record with a low volume recording (classical music, or silent grooves on the testrecord), turn the volume from your amplifier up to the level you can hear rumble and other noise. Then turn off the idledrive but leave the needle on the record, the record is still spinning. In my case the noise for 75% disappears. So in my case most of the noise comes from the idlerwheel and (AC)motor. The remaining 25% noise is mostly surface noise, recording noise and of course the platter bearing.
Why choose a magnetic bearing?:
1- it is more silent than a conventional inverted bearing.
and maybe with a beltdrive:
2-less resistance
and, but I think difficult to design:
3-you can use it as a spring to eliminate low frequency noise.
# one is the main reason and I have confirmed this by using my stethoscope to detect rumble. There is less noise with a magnetic bearing.
# two is of no (or negligible) importance with an idlerdrive. With a belt drive depending on the elasticity of the belt, I can imagine there can be some benefit. My experience is that the resistance of a magnetic bearing is almost the same as an inverted bearing. I tested this with my TT by timing until the platter stops after stopping the drive (the magnetic bearing had more resistance but as YNWOAN noticed this is maybe caused by unparallel magnets (I used a CNC-machine for the upper magnet but the use was impossible for the lower magnet so that was done by hand, although in my mk2 version the lower magnet was made adjustable to adjust parallelism). Personally I think the bearing resistance is also with a belt drive of no effect on sound, but maybe I am wrong on this one.
# three can be of use eliminating lower frequencies and room vibrations. But my theory is that there must be absolutely NO play between the arm and the platter. This is in my opinion the whole problem with decoupling the arm from the platter with a subchassis or in this case a spring bearing. The positive thing about this solution is with a magnetic bearing the movement is only vertical and not horizontal, so variations in distance between the groove and the cartridge are to a minimum. Oshifis I think this is not something to calculate, after calculations you always have to measure to check it. There is not enough reference to validate your calculation in this particular case. You can do this with a or a vibration meter or bearing checker. For me this whole idea is interesting but to complicated.
My conclusions, a magnetic bearing is useful to reduce noise. Go for it!
Graeme UK: First why using a magnetic bearing? To me because a magnetic bearing is more quiet than a inverted one. Less resistance (if there is less) makes no sense, at least not for an idlerdrive.
Mine idlerdrive isn’t that quiet, maybe yours is. A simple experiment to test it. Choose a record with a low volume recording (classical music, or silent grooves on the testrecord), turn the volume from your amplifier up to the level you can hear rumble and other noise. Then turn off the idledrive but leave the needle on the record, the record is still spinning. In my case the noise for 75% disappears. So in my case most of the noise comes from the idlerwheel and (AC)motor. The remaining 25% noise is mostly surface noise, recording noise and of course the platter bearing.
Why choose a magnetic bearing?:
1- it is more silent than a conventional inverted bearing.
and maybe with a beltdrive:
2-less resistance
and, but I think difficult to design:
3-you can use it as a spring to eliminate low frequency noise.
# one is the main reason and I have confirmed this by using my stethoscope to detect rumble. There is less noise with a magnetic bearing.
# two is of no (or negligible) importance with an idlerdrive. With a belt drive depending on the elasticity of the belt, I can imagine there can be some benefit. My experience is that the resistance of a magnetic bearing is almost the same as an inverted bearing. I tested this with my TT by timing until the platter stops after stopping the drive (the magnetic bearing had more resistance but as YNWOAN noticed this is maybe caused by unparallel magnets (I used a CNC-machine for the upper magnet but the use was impossible for the lower magnet so that was done by hand, although in my mk2 version the lower magnet was made adjustable to adjust parallelism). Personally I think the bearing resistance is also with a belt drive of no effect on sound, but maybe I am wrong on this one.
# three can be of use eliminating lower frequencies and room vibrations. But my theory is that there must be absolutely NO play between the arm and the platter. This is in my opinion the whole problem with decoupling the arm from the platter with a subchassis or in this case a spring bearing. The positive thing about this solution is with a magnetic bearing the movement is only vertical and not horizontal, so variations in distance between the groove and the cartridge are to a minimum. Oshifis I think this is not something to calculate, after calculations you always have to measure to check it. There is not enough reference to validate your calculation in this particular case. You can do this with a or a vibration meter or bearing checker. For me this whole idea is interesting but to complicated.
My conclusions, a magnetic bearing is useful to reduce noise. Go for it!
I was after the quietest bearing, but mine is silent as far as i can tell anyway.
Ill listen more carefully next time im awake in the middle of the night and everythings quiet.
I tried your tip of turning the power off, disengaging the idler while playing a quiet patch to see what happens.
Found a quiet patch, turned volume up high, switched of motor power, makes no difference at all! seems i have zero noise getting from the motor/idler wheel to the stylus.
VERY happy about that!
Again, ill try this at the dead of night too and see if there really is absolutely none at all.
Ill listen more carefully next time im awake in the middle of the night and everythings quiet.
I tried your tip of turning the power off, disengaging the idler while playing a quiet patch to see what happens.
Found a quiet patch, turned volume up high, switched of motor power, makes no difference at all! seems i have zero noise getting from the motor/idler wheel to the stylus.
VERY happy about that!
Again, ill try this at the dead of night too and see if there really is absolutely none at all.
Graeme UK, You must be very happy indeed! No noise at all?? In most cases there is always some surfacenoise from the record/needle, depending on the type of cartridge, needle, needleforce and the record itself.
I repeated the test today on my TT. When I turn the volume up to 95% there is some rumble. And about 75% is from the motor and idlerwheel. I modified the inverted ceramic/steel bearing with Teflon a month ago and this made the bearing a little bit more quiet. So most of the noise is from my motor. I am currently researching to change the AC motor into a DC one.
Are you also using a Garrard?
I repeated the test today on my TT. When I turn the volume up to 95% there is some rumble. And about 75% is from the motor and idlerwheel. I modified the inverted ceramic/steel bearing with Teflon a month ago and this made the bearing a little bit more quiet. So most of the noise is from my motor. I am currently researching to change the AC motor into a DC one.
Are you also using a Garrard?
No, im using a lenco.
There is still some background noise but very little. Quiet roar that you can only really hear at high volume on silent parts between tracks and any pops or groove damage.
The none at all comment was extra sound coming from the motor or the idler wheel. The slight amount of background noise doesnt change when i switch off the motor and disengage the idler wheel.
I am very happy with my TT, but its heavily modded, stripped down, chopped up and mounted in 60 kilo of slate.
There is still some background noise but very little. Quiet roar that you can only really hear at high volume on silent parts between tracks and any pops or groove damage.
The none at all comment was extra sound coming from the motor or the idler wheel. The slight amount of background noise doesnt change when i switch off the motor and disengage the idler wheel.
I am very happy with my TT, but its heavily modded, stripped down, chopped up and mounted in 60 kilo of slate.
What would you guys think of a magnetic bearing on a direct drive TT like the Technics family?
My thinking is that the platter drive method is important with magnetic bearing:
- if it's belt drive, it pulls the platter bearing shaft against it's seating causing more side friction & noise than necessary.
- Idler drive is not practical
- Direct drive has no side pressure, I think, & therefore less friction/noise
But does the electromagnetic drive mechanism interact with the magnetic rings needed for a mag bearing?
Is there a technical problem with doing this - has anybody done it?
My thinking is that the platter drive method is important with magnetic bearing:
- if it's belt drive, it pulls the platter bearing shaft against it's seating causing more side friction & noise than necessary.
- Idler drive is not practical
- Direct drive has no side pressure, I think, & therefore less friction/noise
But does the electromagnetic drive mechanism interact with the magnetic rings needed for a mag bearing?
Is there a technical problem with doing this - has anybody done it?
yep, in theory, direct drive with mag lev bearing seems like a good idea but I'm not sure if there are some gotchas in there!
For instance, does the electromagnetic drive mechanism of DD TTs interact with the mag lev. Both of these mechanisms would be physically near one another and may well interact?
Speaking of magnetic interaction, I recently bought some Metglas foil as a magnetic shield for some sensitive preamp tubes, 6AR8 used by John Swenson. Haven't used it yet but it occurred to me that this foil or similar may be used to shield cartridges from magnetic effects http://www.lessemf.com/mag-shld.html
Here's what i would like to audition - a Technics DD TT with mag lev bearing & air bearing tonearm. Has anybody built such a thing?
For instance, does the electromagnetic drive mechanism of DD TTs interact with the mag lev. Both of these mechanisms would be physically near one another and may well interact?
Speaking of magnetic interaction, I recently bought some Metglas foil as a magnetic shield for some sensitive preamp tubes, 6AR8 used by John Swenson. Haven't used it yet but it occurred to me that this foil or similar may be used to shield cartridges from magnetic effects http://www.lessemf.com/mag-shld.html
Here's what i would like to audition - a Technics DD TT with mag lev bearing & air bearing tonearm. Has anybody built such a thing?
All forces from a belt or idler wheel aside, would it be possible to build a mag lev that uses magnets instead of a center bearing to maintain the platters horizontal location in space? I'm working on a solution for rotation at the moment that will not impart any horizontal forces on the platter, so that's not an issue. So, can we make a platter hover?
I recall that that decision was based on the problem of the forces of the belt or idler wheel. I wish I had access to a CNC machine 
oh the mess I would make! I will have to draw up a couple of my ideas on CAD and post them hear so you guys can tell me how incredibly unrealistic I am.
-Justin
oh the mess I would make! I will have to draw up a couple of my ideas on CAD and post them hear so you guys can tell me how incredibly unrealistic I am.-Justin
I believe the answer is no!
I can't remember the physics law quoted (you can't change the laws of nature) but you will find it with a search on DIYA. IIRC, it is a non stable environment and will slip laterally unless prevented in some way!
But is what I'm proposing not close? I ask this in ignorance of how a DD turntable actually works. Does it use an ordinary spindle bearing but if levitated off this bearing (magnetically), would the stator of the DD motor keep the spindle centered?
There's an electromagnetic mechanism turning the spindle & hence the platter & I'm thinking that this is also acting to centre the spindle between the surrounding magnetic fields! Correct me if I'm wrong!
It's been a question that's been bugging me for a while
I can't remember the physics law quoted (you can't change the laws of nature) but you will find it with a search on DIYA. IIRC, it is a non stable environment and will slip laterally unless prevented in some way!
But is what I'm proposing not close? I ask this in ignorance of how a DD turntable actually works. Does it use an ordinary spindle bearing but if levitated off this bearing (magnetically), would the stator of the DD motor keep the spindle centered?
There's an electromagnetic mechanism turning the spindle & hence the platter & I'm thinking that this is also acting to centre the spindle between the surrounding magnetic fields! Correct me if I'm wrong!
It's been a question that's been bugging me for a while
It certainly might; the spinning globe maglev toys I've seen don't have - IIRC - noticeable wobble, but I haven't observed them closely, and a very small wobble would still be an issue for a cartridge. But possibly no more so than the combination of eccentricity and warp one sometimes gets with a standard platter.
A more important question to me is, what problem is the magnetic bearing trying to solve? For many drives, the bearing drag is a help in keeping the speed constant; and bearing wear doesn't seem to be a really critical issue with real-life designs.
Regards.
Aengus
I would also worry about how the platter could be spun - a belt would pull the platter off it's mag centre of stability (which actually doesn't exist until the platter is spinning anyway) The whole arrangement is too unstable to trust a valuable cartridge to it's mercy.
I believe a reduction of bearing/friction noise is the objective
I believe a reduction of bearing/friction noise is the objective
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