Opus 3 Cantus parallel tracking arm

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fdegrove: Even the most complex cutting lathe seems pretty mundane next to that rig.

Clearaudio has a tendency to over-engineer their gears - after all, how else can they charge people $9000 for such a beast? Conceptually the TT2 arm is really simple and if you take the glass tube out with the armwand, it's essentially a fancy version of the Cantus.

fdegrove: the idea to use convex bearing housings being to reduce contact area?

I believe so and I wonder if Clearaudio took into account of Cantus' idea of limiting vertical movement. They are visually similar but I have a feeling CA doesn't subscribe to all of Cantus' design features. I think rounded corners helps the "swinging" inside the tube - not a bad thing.

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Linear Motion Bearings

I looked into the linear motion bearing industry and come away with some amazing products. Miniature linear motion bushings. Maybe not as low friction and low noise as air-bearing but it's worth investigating.

IKO Stroke Ball Spline G LS | Products | IKO NIPPON THOMPSON

IKO Linear Ball Spline G | Products | IKO NIPPON THOMPSON

IKO Miniature Stroke Rotary Bushing | Products | IKO NIPPON THOMPSON

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diyAudio Senior Member
Joined 2002
Hi,

Congrats. :cool:

Overcoming friction in a tangential tonearm isn't a big deal for as long at this friction is a constant.

Much more difficult to tackle is to tell the cartridge induced vibrations where to go and stay untill they convert into heat.
No big deal with high compliance carts and their very limited dynamic range but..........

Cheers, ;)
 
Here's a tonearm originally designed for cylinder recordings that uses mechanical bearings.

Phonograph Makers: Norman Bruderhofer & Matthias Menz

bruderhofer2-5.jpg


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convex bearings

Hi,

WOW.
Even the most complex cutting lathe seems pretty mundane next to that rig.

BTW, the idea to use convex bearing housings being to reduce contact area?

Cheers, ;)

Hi Frank et al,

Here is the latest development on my project. Previously said I was going to get better bearings than my junkbox ones. Yesterday I got some ABEC7 bearings with well finished corners (radiused) and light oil lubricant. Going to remove that. Also found in the junk box two 5/8 inch precision stainless steel rods about 8" long. These were originally for use in computer line printers at DEC in Ireland and have been gathering dust for about 15 years. Decided to us them instead of glass V or inside surface of some kind of tube. See the photo at www.gis.net/~bgruhn/audiodiy. In using the rod for rails and resting the bearings in the V between them it was primarily to reduce contact area and to have the contour of the rail constantly dropping away from the bearing for reducing the friction as the arm had to travel vertically. Between the new track and the new bearings, the results are just what I was trying to get. It tracks perfectly, no stick/slip that I can see and easily does so with the Ortofon cartridge. Now to come up with the rest of the design so it looks professional and is a lot more friendly to use than the jury rig it is now. Also need to flush the bearings of oil to use them dry. They didn't have any dry ones in stock at the bearing place. If the link to my web page isn't working try typing the url into your browser plz.

BillG
 
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bgruhn: "In using the rod for rails and resting the bearings in the V between them it was primarily to reduce contact area and to have the contour of the rail constantly dropping away from the bearing for reducing the friction as the arm had to travel vertically. Between the new track and the new bearings, the results are just what I was trying to get. It tracks perfectly, no stick/slip that I can see and easily does so with the Ortofon cartridge."

Thanks for the update and great picture! I proposed the two rod rail in post#62 and I am glad that it's working well for you. It's great to see something actually working to make music. How encouraging! Please continue to update the progress. Thanks again.

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Radial play

Peter: my comments here are given in the context of DIY. Most DIY builders do not have the ability to machine a glass tube. A stainless tube can be machined and polished to a precision inside diametre at any good machine shop or by those with the know how and their own equipment. This would I expect result in satisfactory results. I agree that the combination chosen by Bo is probably offers the best outcome and performance for the reasons you stated.
I had mentioned that the trolley would move up the inside of the tube during sever warps. I was under the impression that it was either Rauna or yourself that spoke about the bearings used and that they have built in play in the race to allow for arm motion. If I am in error then I apologize for misleading readers and stand corrected. I will re read correspondence to see where this impression originated.

At the risk of flogging a dead horse, I raise this subject again. One of the specs of single row ball bearings calls out the tolerances for radial play. The higher class ball bearings abec 7 has less radial play than the lower abec numbers. So if vertical motion of the arm was the only parameter to consider, the lesser bearing would be the one to choose sacrificing smoothness, starting torque, running torque, sticking here and there etc. I have chosen to go with the abec 7 for now and so far it is working out well. What I am commenting on here is my observation of the bearing in actual operation playing a record. It is easy to see that for the normal vertical motion of the arm, tracking a modestly warped disk, the outer ball race remains stationary for radial motion with the inner race supplying all the vertical motion. The outer race continuously is rotating to supply the horizontal motion. It should be noted that the compliance of the cartridge cantilever provides a buildup of horizontal force from zero to some value just greater than the force required to start the bearing rolling. For a very good quality bearing this is very small and approximates continuous motion of the trolley/arm wand. So yes, the bearings do have built in play with the better ones having less (radial) play. I've no idea whether or not Bo calls out a value for this or specially selects his bearing for this but it is there whether or not you might want it.

BillG
 
abec ratings

Hi,

ABEC ratings don't tell you much about a bearing oher than general nominal tolerances for industrial appications.

Cheers, ;)

Especially if they all come off the same production run and are then sorted into 3-5-7 or good-better-best. I did see and compare abec 5 against abec 7 for the bearings I bought. The 5 had visibly greater radial play and I could swear the 7 surface finish "looked" smoother or better or shinier, especially on the rounded corners of the outer race. OK, I admit it, no scientific measurements here. Just my eyeball and running a fingernail over the edge in question.

BillG
 
A better quality of bearing will result in a smoother lower friction rolling action of the trolley. Tighter tolerance will make for less arm motion which should result in greater dynamic contrast. The cartridge will simply tell the arm to tell the trolley to ride the wall for a bit when a warp comes along. I think that the curved bearing profile used by CA is a compromise so that the arm wand can rock and roll to accommodate warps. I think that when a rich person pays over $10,000.00 for an arm they expect it to play what ever disk they choose to slap onto the platter no matter the condition.

Frank: would you care to elaborate on your thoughts with respect to dealing with cartridge induced vibration in a tone arm? Thanks and best regards Moray James.
 
diyAudio Senior Member
Joined 2002
Hi,

A better quality bearing certainly helps but unfortunately ABEC ratings alone aren't really helpful when it comes to picking a quality bearing.

Keep in mind that the bearings you'd use for this kind of application run virtually unloaded so to reduce chatter (micro-chatter as it really is) it can be helpful to add some load and choose the materials you use in such a way that whatever energy that wanders through the system can be channeled away and dissipated.

Frank: would you care to elaborate on your thoughts with respect to dealing with cartridge induced vibration in a tone arm? Thanks and best regards Moray James.

Certainly can. Fire away I'd say or if you had something else in mind, just let me know.

Just so you know where I'm coming from:

I do try to take a holistic approach to this in that I strongly belief that TT, cartridge, tonearm and how you isolate it from the environment needs to be seen as an entity not just a number of parts that one hopes will find a symbiotic environment by mere coincidence.
That said, I not intimately familiar with the Cantus tonearm so I can only speak for what I know to work for most tangential trackers and radially tracking pivoted arms.
I'm also not particularly at home with high compliance cartridges for the simple reason that, to my ears at least, they're just not good at perveying the dynamic range available from good stereo recording. That just my opinion, YMMV.

So, in a word, yes, I'll try to add my :2c: if I can.

Cheers, ;)
 
In an arm design such as the Cantus the bearings will have some amount of slack (all bearings must have some play so they can move) so lets say that the bearings are a constant and that there is probably not much possibility to lose or dissipate any vibration there since lubrication will add too much drag. So then we are looking at the arm assembly as the primary place at which we can look to eat up any unwanted vibration generated by the cartridge.
One of the members here built a long version of a Well Tempered Arm (I think it was about 14 inches long). This fellow looked into damping for his thin wall arm tube and found that arrow makers use fine powder to damp arrow shaft vibrations. The Cantus uses small diametre thin wall stainless tubes for the arm assembly to force arm resonances up very high in frequency. I suppose that a thin wall constrained layer damping could be applied to the Cantus arm tubes to eat up some vibration. One would have to balance improvement as a result of applied damping with the added moving mass as a result of that damping. Other possible options could be an application of say shrink tube on the arm members one could even use an adhesive lined heat shrink but this would also add the additional mass of the adhesive used in the shrink tube. Other possible methods might be to use a material for the arm wand which was in itself mechanically very lossy so less rigid. One way you are attempting to make the arm assembly very stiff and light so resonance is very high and more easily damped . The other approach would be to make the arm wand material just rigid enough to support itself and the cartridge solidly but from a material light enough and lossy enough (internally) to not support structural resonance within the audio band. Other methods might be stiff but light open cell foam like the kind used for floral arrangements work. There is also open cell glass foam made by Corning for use as a cryo insulation. Another option I had considered and looked into would be organic foam. This could be made of many materials. The first that came to mind was bread made from wheat. When dried it is very light and rigid. The natural cellular structure of bread foam is very random so it would naturally not want to support resonance within the material. The second foam of this kind that I have looked into would be to take wood in a powder (from sanding) and to make a bread with wood powder as the "flour". I think that Sitka spruce would have probably the widest most even resonant signature with in the voice band range. Sitka spruce is the preferred wood for most string instrument and piano sounding boards for this reason. If additional damping were required the open cell structure would permit loading of the open cell structure with fine powder damping. These are just some ideas which I offer for discussion. I may well be missing some more obvious means of damping the arm wand. So Frank if you have any comments or suggestions I would welcome discussing them with you.
With a design such as the Cantus where the arm carriage assembly has been placed above the record surface the path from the bearings to the plinth is not very direct so probably not capable of much direct energy "sinking". If the horizontal carriage track were situated behind the platter and hard mounted to the plinth then one could count on substantially grater energy sinking capability directly to the plinth. So right now I see the arm wand assembly as the primary location for dissipating unwanted cartridge induced vibration. I suppose that if one had access to sophisticated measurement equipment then one might consider using some form of compliant coupling between the arm wand and the carriage assembly. That could work but it might prove more difficult to achieve, I don't know. I look forward to your thoughts.
 
diyAudio Senior Member
Joined 2002
Hi,

Before I make any further comments, do I assume you have such an arm and want to improve it or do you want to design from scratch?

Assuming an Opus 3 Cantus I'm having trouble accepting the self-resonance of the tubes connecting the cartridge platform to be outside the audio-band, upper mid to early highs maybe.
Either way that's irrelevant as the assembly will resonate as a whole even if parts of it are mechanically decoupled.
High frequency resonances equate high speed activity of low energy content so these need something to sink them in so the can't keep on travelling back and forth untill they eventually are convected to heat. Let's not forget, the arm assembly is continuously excited by the cartridge as it tracks the record and you do not want that energy to be picked up by the stylus again.

What can you do about it?

You could use a material with a low self-resonance for the arm tube provided it is outside the audio band (say 3 to 5 Hz) and it is still stiff enough to allow accurate tracking of the cartidge.
A piece of composite fiber arrow may do the trick, unidirectional lay-up with low epoxy content and lots of carbon dust should make it pretty much inert.

As said, this assumes a low compliance cartridge.
Looking at the Cantus, I think this is not a design that has been developed with low compliance cartridges in mind.
You could however try a couple of tricks: tighten one of the cartridges mounting bolts firmly and just hand tighten the other one so it can't rattle.
The tightly tightended bolt is now your preference path (it presents a low mechanichal resistance).
Look along the path of travel towards the plinth of your TT and see if there's any spot where you can apply the same principle.
Keep in mind that in creating preference paths you will need to think in terms of a spike as you'd use them under a loudspeaker (for instance).
Small contact area at high pressure point allows for energy to be drained, big contact area disperses the prefered path making it hard for the energy to travel back.
Tiptoe theory really except uni-pivot arms is where this was first apllied even though not without difficulty (obviously).

Hopefully this is of some help to some of you. I'm just rewriting it again as it crosses my mind.

Now, if there is anyone following this thread with listening experience on various tangential tracking tonearm designs, I'd like to hear about the "sonic" pros and cons of the Cantus design versus say, something like an airbearing design a la Air Tangent or Eminent Technology for instance.
Or, alternatively, if you do have a Cantus, what do you think is wrong with it?
I know, I am asking quite a lot...:cool:

Cheers, :)
 
fdegrove: "A piece of composite fiber arrow may do the trick, unidirectional lay-up with low epoxy content and lots of carbon dust should make it pretty much inert."

The Clearaudo TT2 uses a carbon fiber armtube. Do you think that's on the right track? I also notice there's a piece of metal mounted vertical on the armtube before the headshell. I wonder what that's for. Maybe for damping?

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10K for an arm

A better quality of bearing will result in a smoother lower friction rolling action of the trolley. Tighter tolerance will make for less arm motion which should result in greater dynamic contrast. The cartridge will simply tell the arm to tell the trolley to ride the wall for a bit when a warp comes along. I think that the curved bearing profile used by CA is a compromise so that the arm wand can rock and roll to accommodate warps. I think that when a rich person pays over $10,000.00 for an arm they expect it to play what ever disk they choose to slap onto the platter no matter the condition.

Frank: would you care to elaborate on your thoughts with respect to dealing with cartridge induced vibration in a tone arm? Thanks and best regards Moray James.

Hi, I would expect anyone spending 10K for an arm would have his collection of discs in utterly pristine condition so the arm would have no excuse for playing it perfectly. Now to tonight's progress report.

We have been thrashing about on bearing quality and the ability of ball bearings to allow a trolley to traverse the rails with some degree of success. I have been at that point for a few weeks now. I haven't refined mountings, and leveled the rails and the TT with any degree of precision yet. What I found so far is that with every upgrade of the trolley, less weight, better bearings, running dry vs lubed, improved rails etc, my test arm tracks well, sounds great and has no trouble with the trolley being dragged across the record but is becoming far more sensitive to the odd speck in the groove and tapping a finger on the plinth. These impulses send the cartridge into a fit with the stylus jumping grooves. Any arm that sensitive is not for me. I never saw such stuff going on with my version of the WT Arm or the Schroeder clone. Now if a stylus on an arm can drive a disc or golf ball suspended in 10,000cs silicon fluid or a rudimentary eddy current brake, then maybe the rolling friction is already as low as it needs to be and the ability of the bearing and the very smooth mating surfaces of outer bearing race and track rods is is allowing the stylus and arm to simply jump out of the groove.

So I filled a small tin can cover with 1000cs (viscosity)silicone fluid. put a short (1.5") piece of magnet wire on the back end of the counterweight shaft, wound a couple turns of the wire around a nail to make a very small paddle and immersed it in the fluid. This tiny bit of damping seems to tame the impulse response completely. It also makes the arm far more civilized and user friendly. WOW! I can thump on the plinth with my finger, slight bass sound but it keeps tracking, hit the side of the record, same. What about the sound? Can't say yet. The few records I've listened to sounded like what I expected them to. Maybe I can use even less viscous fluid, maybe don't need to. I'm not wild about the fluid filled trough, so perhaps an eddy current brake is in order.

I've lost sight of who if any in this forum actually has a Cantus or other linear tracking tone arm. So if we have a user, please give input on the vertical sensitivity to shock and vibration and what if anything is done to tame it. Thanks,


BillG

BillG
 
I know Mr Hansson personally and have listened to Cantus a many occasions through his large hornsystem. The bass is built from the cellar and up and goes down to 16Hz:cool:(it is about 6meters long with its opening behind the sofa to get phase right with the mid).

The arm is mounted in his Continuo. There are no problems with shock and vibration sensitivity. This might be due to the low mass of the arm or it might also be an effect of the very high mass in the Continuo.
 
Frank: I have a Continuo/Cantus on the way along with a separate Cantus for my brothers TT. They should be here in a few weeks. My interest is in possible tweaks to the stock arm. Depending upon how the table arm combination sound I might be interested in building from scratch but that would be a long project which would require a lot of thought and so my interest to discuss ideas here.
I agree that the smaller arm tubes of the Cantus will not push resonance up out of the audio band but any increase in frequency is a good thing. I asked Bo about this last year and he told me that he had experimented with large dia. arm wands and when playing a blank disk he said that the feedback break through was at a much lower level for a large tube compared with the small dia. tubes. Bo told me that at normal playback levels tube resonance (of a large dia. tube) were noticeable even with damping applied to the tube.

Quote:"You could use a material with a low self-resonance for the arm tube provided it is outside the audio band (say 3 to 5 Hz) and it is still stiff enough to allow accurate tracking of the cartridge.
A piece of composite fiber arrow may do the trick, unidirectional lay-up with low epoxy content and lots of carbon dust should make it pretty much inert."

Frank: the example that you provide seems to me to be a stiff structure so I cannot see how this could have a self resonance of 3-5 Hz. Perhaps you could elaborate on this further?
I was thinking that a laminate of a light high loss material like Balsa might work.
Weights that could be placed along an arm wand to break up standing waves might also be an idea.
It seems to me that in a Cantus arm that introducing materials with high internal loss is probably the easiest way to eat up excess energy generated by the cartridge but care will be required to keep overall mass as low as possible.

I have listened to air bearing arms in the past but it has been some time and I do not have access to them any longer. It is my estimate that an air or magnetic bearing will have compliance's which will be difficult or impossible to damp. The use of a mechanical bearing provides physical contact and the ability to sink energy to the support structure where it can be dissipated. I would expect that a mechanical design should sound better than air or magnetic bearing systems.

Directdriver: regarding the large conical tipped rod in the CA arm wand may well be a means of mass damping the primary structural resonant point along the arm. That's just a guess but some considerable mass would be required to do this. Is there anybody who has be given an explanation as to the purpose of this device?
 
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