Every post I see of yours is raining on someone's parade. If you don't have anything constructive to add don't say anything at all.
Some of us are retired, HIFI or sound reproduction is our hobby and these projects keep us busy.
Like this. This isolation station worked extremely well, as good as my current Minus K, the BUT is I could not keep the TT level. Creep in the bungee chords of only 1mm would significantly effect level. Vertical isolation was better than 1Hz.
The problem with hanging a platter would be the pendulum effect. A pendulum has a natural frequency of resonance, Conrad posted the formula for calculating this. A better solution is to use an inverted bearing where the point of rotation is coincident with the COG of the platter, the bearing then needs no sleeve, all it will need is a very thin retaining ring at the bottom of the housing so the platter doesn't tilt when the stylus is cued down.
A platter bearing built like this does not need the TT to be level as the platter will spin with minimal wobble at any angle.
The major problems with a regular TT bearing is the very small journal diameter most use journals 12mm or less in OD. These small journals do not spin fast enough to provide enough oil pressure to prevent the journal and sleeve coming into contact. Some high end TT's use a pump to pressurise the oil in the bearing. I have a Technics SP10mk2 and the precession of the bearing causes about 0.1mm pulsing runout measured on top of the platter.
Did it also work like a Foucault pendulum when the platter is spinning? Would be very interesting, but not so good for audio.
Hi rickmcinnis and Hi warrjon,
I have had a very slow start building my turntable.
Before I make anything, I completely finish the design and make engineering drawings of each part. (to ANSI specs yet) I have done that during all of my professional life and I don't want to change!
However, the design is done and I have already made one part. I have spent approximately US$ 600 on raw materials and I am past the point of no return. The platter consists of two parts, each .750" thick. The two facing surfaces will have six pockets each machined into them. These pockets will be filled with #12 lead shot and then back-filled with bee's wax to prevent the shot from shifting.
Of all the friends I have, one has written the CNC program to machine the pockets and I am waiting for a date from one of my other friends to use his CNC milling machine to mill the pockets.
I will document as much as possible with a new camera I have purchased.
Warrjon, I am amazed at your suggestion of supporting a turntable with an inverted bearing whose spherical center of rotation coincides with the center of gravity of the spinning mass, because that is exactly what I plan to do. I have a different approach as to how to support the bottom end of the turntable pivot though.
I hope that, when I reveal my bearing idea, that you won't say that, I stole the idea from you.
Sincerely,
Ralf
I have had a very slow start building my turntable.
Before I make anything, I completely finish the design and make engineering drawings of each part. (to ANSI specs yet) I have done that during all of my professional life and I don't want to change!
However, the design is done and I have already made one part. I have spent approximately US$ 600 on raw materials and I am past the point of no return. The platter consists of two parts, each .750" thick. The two facing surfaces will have six pockets each machined into them. These pockets will be filled with #12 lead shot and then back-filled with bee's wax to prevent the shot from shifting.
Of all the friends I have, one has written the CNC program to machine the pockets and I am waiting for a date from one of my other friends to use his CNC milling machine to mill the pockets.
I will document as much as possible with a new camera I have purchased.
Warrjon, I am amazed at your suggestion of supporting a turntable with an inverted bearing whose spherical center of rotation coincides with the center of gravity of the spinning mass, because that is exactly what I plan to do. I have a different approach as to how to support the bottom end of the turntable pivot though.
I hope that, when I reveal my bearing idea, that you won't say that, I stole the idea from you.
Sincerely,
Ralf
There are loads of TT's that use inverted bearings, but most position the pivot point too high above the COG of the platter and use a full sleeve.
I mentioned it because I started on an inverted bearing design for a Technics SP10mk2 motor a few months ago. One of my SP10 motors has a damaged bearing so this will be the guinea pig. I bought a 2mm carbide ball and sapphire cup from True Point in the UK, these are Pink Triangle platter pivots. It will not use a journal bearing, the sleeve will have a very small retaining ring at the bottom.
I mentioned it because I started on an inverted bearing design for a Technics SP10mk2 motor a few months ago. One of my SP10 motors has a damaged bearing so this will be the guinea pig. I bought a 2mm carbide ball and sapphire cup from True Point in the UK, these are Pink Triangle platter pivots. It will not use a journal bearing, the sleeve will have a very small retaining ring at the bottom.
Hi rif,
I may have seen a Foucault pendulum.
Many years ago I visited the Capitol in Washington, DC.
on the "main floor" there was a swinging pendulum, fastened way up in the cupula.
Around the pendulum there were a large number of ~4" tall little "persons" arranged in a large circle.
As the pendulum swung in its plane of oscillation and being stable with respect to space, it sequentially knocked over the little "persons". It would have taken twenty four hours to see all the little "persons" knocked over and I didn't have the time available.
Was that a Foucault pendulum? If it was, how does that relate to turn tables?
Sincerely,
Ralf
Hi warrjon,
I am aware of that. It is the combination of the center of gravity and the center of the spherical bearing that I made reference to.
Sincerely,
Ralf
Yes, that is a foucault pendulum. It does that because the earth is spinning - , I think the physics term is non-inertial frame of reference. Similar for the coriolis effect - water spins when going down a drain. One way in the northern hemisphere, the opposite in the southern.
It relates to your suspended turntable since you have a pendulum with a spinning mass attached to it. I was wondering if that would cause the same effect.
Please don't misunderstand me, these are very small effects and I'm not criticizing your designs. As you noticed, it took a very long pendulum to produce a small visible effect below.
Glad to hear things are proceeding. Nothing like the point of no return. A great motivator almost as effective as fear.
Take care,
Take care,
I wonder if it is safe for you to discuss your idea?
Are you willing to give it a try? I would like to know how you are progressing.
Are you willing to give it a try? I would like to know how you are progressing.
There is a way.
Angle the bungee cords so it foms a sort of inverted pyramid and connect them to the sprung mass at a height significantly above the centre of gravity, such that a line extending from each bungee cord passes through the centre of gravity of the sprung mass. I can't sketch it right now, you'll have to visualise it. In plan view, the upper connection points form a larger square than the lower connection points. The sprung mass frame will have to extend upwards, to provide the connection points.
Any force applied at the CoG results in pure translation, but the system is much more pitch/yaw stable and less sensitive to changing bungee characteristics. I would angle the bungee cords at about 30 to 45 degrees from the vertical. They can be shorter and stiffer for the same degree of isolation.
Cheers,
Mike
@mikey_audiogeek The frame was as wide as possible to fit where is was placed. The bungee cords were angled by about 5deg which was the max the frame would allow. This frame has since been replaced with a Minus K.
Hi rickmcinnis,
Good timing. I finally got the first CNC work done. I had to wait for my friend to take a day off from work so that I could use his CNC machine. That was on the 19th of August. Today I am too tired from shopping but tomorrow I'll have some photos.
Sincerely,
Ralf