Hi Bibio
That would certainly work except that the length of the knife edge would have to be at least four inches plus the distance between bearings! There might be a problem with mass.
Sincerely,
Ralf
That would certainly work except that the length of the knife edge would have to be at least four inches plus the distance between bearings! There might be a problem with mass.
Sincerely,
Ralf
not if you use multiple bearings. make it so it's only contacting 2-3 bearings at a time.
yes it would be a mare to get right but i think it would work.
Hello gaborbela
Please read the following carefully.
A tone arm tracking the groove in an eccentric LP, moves away from the label during one half of the revolution of the LP. A pivoting tone arm has no problem with that, but a linear tracker with a weight pulling its carriage toward the label would have to lift the weight during that half of the revolution of the LP. That would be exactly the opposite of what you are trying to accomplish.
Adding a weight to help the carriage to move away from the label, puts you back on square one.
You may also consider that the weight will have to be able to move at least four inches. (the radial distance between the start and the end of the groove)
Sincerely,
Ralf
Please read the following carefully.
A tone arm tracking the groove in an eccentric LP, moves away from the label during one half of the revolution of the LP. A pivoting tone arm has no problem with that, but a linear tracker with a weight pulling its carriage toward the label would have to lift the weight during that half of the revolution of the LP. That would be exactly the opposite of what you are trying to accomplish.
Adding a weight to help the carriage to move away from the label, puts you back on square one.
You may also consider that the weight will have to be able to move at least four inches. (the radial distance between the start and the end of the groove)
Sincerely,
Ralf
Hi Bibio
I took the liberty of making a simple drawing of your idea. It would be interesting to try although the cost of the bearings would be somewhat on the high side.
The bearings would have to have vee-shaped circumferences and their alignment to each other would be critical. The knife edge could be a piece of machined and hard anodized aluminum.
Sincerely,
Ralf
I took the liberty of making a simple drawing of your idea. It would be interesting to try although the cost of the bearings would be somewhat on the high side.
The bearings would have to have vee-shaped circumferences and their alignment to each other would be critical. The knife edge could be a piece of machined and hard anodized aluminum.
Sincerely,
Ralf
The drawing of multiple rollers underneath a blade reminds me of airbearing arm with static rod with holes of streaming air pushing the floating arm assembly a la Forsell. I think two rollers on top riding a blade below is probably simpler?
To right it would be a mare. All the bearings would have to be aligned to an absolutely ridiculous level of accuracy but in theory it would work. If you wanted to use glass rods/tubes for the track the mass would be totally prohibitive. You'd have to revert to using a knife edge and in doing so loose all the the benefits that the glass proffers. But as Frank has shown some ideas that look wrong at first glance can have hidden merits. Build it and prove the concept, you never know.
Niffy
that's exactly what i'm on about
ceramic abec7 bearings are not that badly priced.
i had another think about it and you could use a channel on top of the bearings with the knife on top of the channel, like one of those bearing drawer runners as the sliding mechanism then just place a knife on top.
just an idea i had in my head and i'll probably never get round to it
Your idea sounds a lot like the ladegaard arm. This arm is an air bearing design so bearing alignment won't be an issue. There is a build thread for this arm here:
http://www.diyaudio.com/forums/anal...real-diy-winner.html?highlight=linear+tonearm
Niffy
http://www.diyaudio.com/forums/anal...real-diy-winner.html?highlight=linear+tonearm
Niffy
Always love to read about new ideas , including this one .
2 things coming to mind when looking at the drawing ( nice drawing btw ! ) :
1 : why we want an interupted bearing / knife contact ? there are few points where it rides on either 2 or 3 bearings , which looks like there's not a linear steady contact . instabillity , uneven friction at some points ??
2: think it's pretty difficult to get the amount of bearings perfectly aligned ??
THX
Paul
2 things coming to mind when looking at the drawing ( nice drawing btw ! ) :
1 : why we want an interupted bearing / knife contact ? there are few points where it rides on either 2 or 3 bearings , which looks like there's not a linear steady contact . instabillity , uneven friction at some points ??
2: think it's pretty difficult to get the amount of bearings perfectly aligned ??
THX
Paul
A bit OT , but O so interesting and would like to share with you guys .
Vinyl Records Repair - Grooves Reconstruction - Ultimate solution for scratched records - YouTube
THX
Paul
Vinyl Records Repair - Grooves Reconstruction - Ultimate solution for scratched records - YouTube
THX
Paul
This may be jumping backwards a bit but I've been rereading this thread and thought that this may be of intrest.
Back when the design was single tube 4 bearing I noticed that tracking problems seemed to diminish when the distance between the bearings was reduced so that the edge of the bearings ran about 20degrees from the top of the tube. This makes sense as the shallower this angle is the lower the contact pressure and loading of the bearing will be. The two glass rod design,when using 6mm rods and 4mm wide bearings, also has a contact angle of about 20degrees. A shallower contact angle may help to improve tracking further. (The cantus and clearaudio arms that run inside of a tube will effectively have a zero contact angle.)
At a tracking force of 1.4g a heavily modulated groove produces about 0.8g of stylus drag. With a 30g carriage this. Would result in the bearing being loaded only 1.6degrees off vertical. You could probably make the bearing tube contact angle as little as 10degrees but queuing might get a bit risky. Personally I think the current 20degree contact angle is probably the best compromise.
With the single tube 4 bearing design the vertical pivot was located at the centre of the tube. With the two tube 2 bearing design things are a bit more complex. The pivot doesn't follow a circular arc. But within the small angular range that the arm will experience during use it can be reasonably accurately modelled as a point. For 6mm rods 4mm bearing this point is going to be about 7.4mm above the centre of the rods. This will increase warp wow slightly but as no one has mentioned hearing this on their two tube models I'm not overly concerned. The increased stability that the two tube design offers over the cantus style tube is probably more significant.
Finally, I modelled a slight tweek to the two rod design. Instead of 6mm rods I used 4mm rods separated by a 1.5mm batten, again with 4mm wide bearings. The contact angle is still about 20 degrees, the vertical pivot drops a couple of mm, and the vertical friction remains about the same. As I have some 4mm glass rod I'll give this a go.
Hope this wasn't too long winded and was of interest to someone.
Niffy
Back when the design was single tube 4 bearing I noticed that tracking problems seemed to diminish when the distance between the bearings was reduced so that the edge of the bearings ran about 20degrees from the top of the tube. This makes sense as the shallower this angle is the lower the contact pressure and loading of the bearing will be. The two glass rod design,when using 6mm rods and 4mm wide bearings, also has a contact angle of about 20degrees. A shallower contact angle may help to improve tracking further. (The cantus and clearaudio arms that run inside of a tube will effectively have a zero contact angle.)
At a tracking force of 1.4g a heavily modulated groove produces about 0.8g of stylus drag. With a 30g carriage this. Would result in the bearing being loaded only 1.6degrees off vertical. You could probably make the bearing tube contact angle as little as 10degrees but queuing might get a bit risky. Personally I think the current 20degree contact angle is probably the best compromise.
With the single tube 4 bearing design the vertical pivot was located at the centre of the tube. With the two tube 2 bearing design things are a bit more complex. The pivot doesn't follow a circular arc. But within the small angular range that the arm will experience during use it can be reasonably accurately modelled as a point. For 6mm rods 4mm bearing this point is going to be about 7.4mm above the centre of the rods. This will increase warp wow slightly but as no one has mentioned hearing this on their two tube models I'm not overly concerned. The increased stability that the two tube design offers over the cantus style tube is probably more significant.
Finally, I modelled a slight tweek to the two rod design. Instead of 6mm rods I used 4mm rods separated by a 1.5mm batten, again with 4mm wide bearings. The contact angle is still about 20 degrees, the vertical pivot drops a couple of mm, and the vertical friction remains about the same. As I have some 4mm glass rod I'll give this a go.
Hope this wasn't too long winded and was of interest to someone.
Niffy
Excellent post Niffy.
I've been following this thread since it was pointed out to me back in August of last year.
I have an old ROK L-34 that has been designated as my "Experimental" table, my intention is to re-plinth and experiment with several of the arms as detailed in this thread.
I really liked the recent showing of the DIY arm where the bearings ride on top of the rod that Frank made. I have been thinking along those lines since the beginning. Reasoning for that style is keeping the pivot close to the surface of the vinyl, and while not being able to shorten the arm down to a couple of inches plus, I would be able to shorten it down to a little over 6" in effective length.
In my musings, I am picturing a pair of the concave YoYo bearings riding on a 6mm borosilicate glass rod. By the #'s Niffy just posted would that keep the contact angle in the desired range with a 4mm bearing?
I have a couple of other audio projects to finish in the shop before I can start on the TT, I expect to be sometime this summer before beginning that process.
I'll still be lurking, watching for new developments as they arise though...
John
I've been following this thread since it was pointed out to me back in August of last year.
I have an old ROK L-34 that has been designated as my "Experimental" table, my intention is to re-plinth and experiment with several of the arms as detailed in this thread.
I really liked the recent showing of the DIY arm where the bearings ride on top of the rod that Frank made. I have been thinking along those lines since the beginning. Reasoning for that style is keeping the pivot close to the surface of the vinyl, and while not being able to shorten the arm down to a couple of inches plus, I would be able to shorten it down to a little over 6" in effective length.
In my musings, I am picturing a pair of the concave YoYo bearings riding on a 6mm borosilicate glass rod. By the #'s Niffy just posted would that keep the contact angle in the desired range with a 4mm bearing?
I have a couple of other audio projects to finish in the shop before I can start on the TT, I expect to be sometime this summer before beginning that process.
I'll still be lurking, watching for new developments as they arise though...
John
John
Thanks for the reply.
When using yoyo bearings it is only the outer corners of the concave that want to contact the rod. With a single 6mm glass rod you would want the bearing contact points to be about 2mm apart to give a 20degree contact angle. This would mean that the concave groove in the bearing needs to be 2mm wide. I don't know how wide the groove is in this type of bearing is. A 2mm contact spacing is pretty small making the carriage easy to inadvertently knock off the rail. A slightly larger diameter rod with corresponding wider bearing might be safer. It would also give a higher level of friction to the vertical pivot which was one of the original design aims as mentioned very early in the thread.
Hope this is helpfully
Niffy
Thanks for the reply.
When using yoyo bearings it is only the outer corners of the concave that want to contact the rod. With a single 6mm glass rod you would want the bearing contact points to be about 2mm apart to give a 20degree contact angle. This would mean that the concave groove in the bearing needs to be 2mm wide. I don't know how wide the groove is in this type of bearing is. A 2mm contact spacing is pretty small making the carriage easy to inadvertently knock off the rail. A slightly larger diameter rod with corresponding wider bearing might be safer. It would also give a higher level of friction to the vertical pivot which was one of the original design aims as mentioned very early in the thread.
Hope this is helpfully
Niffy
Hi Niffy,
No, not too long winded at all. My 2 tube track was put together from bearings and tube that I had on hand and have been delighted with it so far. But I've been wondering just how far from optimum my design is. The bearings are 4mm wide but with a very slight radius on the edges reducing that 4mm width by some very small number. The tubes are 10mm O.D. So tonight I took a look at what the contact angle actually is. I come up with 39.869 degrees. Then tried (on paper/autocad) 8mm dia tube for 30 deg and 6mm dia tube for 19.47 degrees. So it looks as though I will buy something by going to 6mm dia tube. It will lower the pivot point some which is good. Since I'm not observing any degradation in sound quality or stability with the present setup what change in audible character do you or anyone else think can be had by making this change? Basically I don't know how bad or good what I have is and I would like to know.
Rgds.
BillG
PS We toss around "improved tracking" or "tracking problems" with reckless abandon and never define what we are talking about. Are we talking about never jumping out of the groove, or always staying in intimate contact with the groove, or what about staying in the groove but rattling around in the groove? I would like to see some better definition and agreement on what limits to place on good or better or improved tracking.
Rgds again,
BillG
Thanks for the comments, Niffy. I see what you are trying to convey, I think. I do not have the bearings in my hand to measure, nor have I found a really good drawing online. (we are talking about YoYo bearings....) I had my own reservations about the arm dislocating with the dimensions I mentioned before. I would question why you think the vertical friction would change by using larger diameter rod, and wider concave bearings ( if indeed they can be found ). Is it because of the change in angle of contact? The contact patch itself would not change materially would it? I think that moving to larger bearings with the correspondent additional weight would be somewhat counterproductive to retaining a low total mass. It may be that a twin-rod/tube with bearing riding centered would indeed be a better solution. This is something to draw and contemplate, Thanks again.
John
Niffy, Bill,
On the 4 bearing the spacing of the bearings was important for the lateral tracking, not the vertical. Vertical tracking, footing in the groove and on warps was and is superior over the 2 bearing two tube design. Can't have both though, and a longer arm is even worse regardless of implementation. What ive discovered is that in a linear arm its better to have a stiffer vertical pivot (sory tracking force gauge worshippers), and free lateral movement with enough load on the bearings to quell any potential chatter. Another addition has been some precarious filling with some 3m memory foam in the drilled out cavities in the carriage T. But at the end of the day, its just my take
Colin
On the 4 bearing the spacing of the bearings was important for the lateral tracking, not the vertical. Vertical tracking, footing in the groove and on warps was and is superior over the 2 bearing two tube design. Can't have both though, and a longer arm is even worse regardless of implementation. What ive discovered is that in a linear arm its better to have a stiffer vertical pivot (sory tracking force gauge worshippers), and free lateral movement with enough load on the bearings to quell any potential chatter. Another addition has been some precarious filling with some 3m memory foam in the drilled out cavities in the carriage T
. But at the end of the day, its just my take Colin
Bill
I'll comment on your second point first. Defining tracking.
Never jumping is of course required. The stylus jumps when the side force equals the vertical tracking force. The side force is caused by bearing friction, acceleration of the carriage and any slope in the track tubes. The actual side force to jump is slightly less due to the forces from groove modulation. Depending on tracking force and compliance the stylus will be displaced by 0.25-0.4mm before it jumps. Again depending on cantilever length this will result in an angular displacement of 2-4.5degees. Even without jumping the cantilever can be off from tangential by several degrees. Worse than a pivoted arm. it is the cantilever that needs to remain tangential, not the armtube. This is the brilliance of Frank's design.
Bearing friction is the main contributer to side force. By reducing this the cantilever will remain more tangential. Look at the cantilever when a record is playing using a strong magnifying glass. If you can see the tip of the cantilever moving relative to the cartridge body then you probably have tracking problems. Typically a 100th of a mm movement here will equate to a 10th of a degree tracking error.
Now the first part.
At bearing/tube contact angles above 45degrees binding becomes a problem. 45degrees is the maximum angle that will work well. Your current set up is a bit close to this. With a 4mm wide bearing I think a 6mm tube is about optimum. This should reduce lateral friction and lower the pivot point. Lower lateral friction will keep the cantilever more tangential. This should improve stereo imaging, improve separation of individual instruments and reduce distortion. I would be very interested to hear what difference thinner rods actually has as this is all theory at this point.
I am hoping to receive some components shortly that will hopefully solve my own tracking problems, eccentric bearings, and will post my findings then, fingers crossed.
Niffy