Tonearm Topology in the Bearing Straits

[Guest]

I was reading the VPI 3D Pivot Conversion Kit thread and – having never owned a VPI or other uni-pivot arm – imaging what the kit does and why it is desirable (or needed.) It came to me that I’m not well versed in tonearm topology – ignorant if you will – particularly about uni-pivots, but also about the issues surrounding topology choices and trade-offs.

My vague sense has the merit of the uni-pivot found in its reduced friction and lack of bearings and their attendant bearing resonance or chatter. I used to own an SME V and now a Tri-Planar and a Kuzma 4Point; those are the basis of my experience; the first two are built using bearings.

Questions 1: what does bearing resonance/chatter sound like? (I presume it is considered distortion and as with so many distortions it may best be detected by its absence.) Are there particular conditions where it may be caused or made more prevalent? Wider grooves, end of side, sympathetic resonance passed through the arm that hits the bearings’ resonance frequency? What should I listen for? Or is bearing resonance always there and you don’t hear it because, well, it’s always there?

Questions 2: is it possible totally to eliminate arm/cartridge/stylus roll in a uni-pivot? Not having owned a uni-pivot, when I think of one I think of the tight-rope walker carrying a very long staff that aids his balance. Some unis have out-rigger weights, some use magnetic force, some do what the the VPI 3D Pivot Conversion Kit does, Etc. – all aimed at keeping the cartridge/stylus upright(?) under conditions where the tight-rope walker’s wire is moving laterally. (yes, not a perfect analogy) Do most uni-pivots set azimuth by "leaning" the arm to one side? (Versus, say, rotating the arm via a worm drive a la Tri and 4P) Can the uni-pivot azimuth stay rock steady given its nature, that is standing or supported on a single point?

My language here is imprecise and reflects my lack of knowledge. Several of you know so much about how arms work and the design of different arms across the years. Hoping to learn something from these less-than-well-formed questions – then I can ask some more. :-)

[Rob]

Good post. I don't think one can hear "bearing chatter" per se, the symptom would be cartridge miss tracking kinda like the tail trying to wag the dog. I do know arms with captive bearings go out of adjustment over time. the SME uses ball bearings, the Tri planar uses needle bearings with sapphire cups both types rely on some degree of pre-loading and are susceptible to going out of adjustment. I sent my Tri Planar into Tri, it was less than 10-yrs since it was last inspected and it required adjustment. that said there are other designs that use one or a combination of: knife bearings, needle bearings and radial bearings, all of which require some sort of adjustment/maintenance.

side to side rocking has been address in uni-pivots quite effectively by the Graham Phantom and Spiral Groove arms w/o resorting to a 2nd bearing, there are undoubtedly more examples of other 'arms members here have experience with.

[Joe Pittman]

I hear/recognise bearing chatter right away after hearing a zillion tonearms over many years (the entry level Rega arms are a good example). I describe it as "mechanical jitter"; the bearings literally buzz at some frequencies. The bearing chatter seams to be excited by all frequencies and especially high frequency high amplitude energy and sounds a bit like mistracking. I like to use Linda Ronstadt's voice which is difficult for a cartridge to track anyway. With a loose bearing, her high notes will lose contact with the groove.

Bearings changing over time is a real phenomena as Rob describes above. Bearings expand and contract almost every day due to temperature change. Over time, this cycling will loosen the bearing tolerance/preload. Ultimate bearing design and manufacture shoots for having the inner and outer ball bearing raceways (in radial ball bearings) to have the same coefficient of expansion (as they expand and contract, the gap is constant and never changes regardless of temperature) . As a side note, it is interesting that tonearms with high precision bearings with preload, were damaged many times in the past due to air shipment from Europe. The warm air/cold air cycle in air shipments was enough to damage bearings due to differential expansion in the airplane cargo hold.

Sopranos are a real challenge. Try "Trio" with Dolly Parton, Linda Ronstadt and Emmylou Harris. They each have a strong voice (especially Harris) and the songs near the end of the sides are great tracking tests.

[Guest]

Thanks for your replies. Are there sonic characteristics (soundstage, dynamics, etc.) associated to one bearing type / topology versus another? Or can we simply not zero-in on that given all the other differences (materials, precision, etc.) between any two arms? I definitely hear differences between the Triplanar and the 4Point.

[MylesBAstor]

I think one has to be arm type agnostic. Andre, Marc and I were having a similar discussion and there's just too many variables that go into the design of an arm to make any generalizations. Geometry. Length. Rigidity. Resonances. As I understand it, the advantage of unipivot are lack of bearing chatter, friction and they can be made more inexpensively. Traditional arms-take the SAT arm-offer stability. But the bearing quality is all important. After all, the ultimate goal is holding the cartridge motionless above the record groove. The SAT is an all out implementation of a gymballed arm and in this case stability and rigidity vs length seems to win out.

Not to mention cartridge/arm interactions. For example Lyras are specifically designed to drain vibrations into the arm. Thus that arm better be free of resonances.

[Guest]

I think one has to be arm type agnostic. Andre, Marc and I were having a similar discussion and there's just too many variables that go into the design of an arm to make any generalizations. Geometry. Length. Rigidity. Resonances. As I understand it, the advantage of unipivot are lack of bearing chatter, friction and they can be made more inexpensively. Traditional arms-take the SAT arm-offer stability. But the bearing quality is all important. After all, the ultimate goal is holding the cartridge motionless above the record groove. The SAT is an all out implementation of a gymballed arm and in this case stability and rigidity vs length seems to win out.

Not to mention cartridge/arm interactions. For example Lyras are specifically designed to drain vibrations into the arm. Thus that arm better be free of resonances.

Which makes me wonder if we'll see an arm with more attention paid to vibration/resonance management, such as an arm mount incorporating Stillpoints or similar. Or built-into the arm itself. Heck, built in to the headshell!

Slightly different - the 4Point topology seems unique - what are its downsides?

[rockitman]

I wonder if unipivots track the inner most grooves better than traditional gimbal type bearing designs ? I hear very little treble dulling with Graham arms...my only unipivot experience. My Clearudio Universal arm (gimbal) from what I recall had noticeable inner groove treble dulling.

[MylesBAstor]

Which makes me wonder if we'll see an arm with more attention paid to vibration/resonance management, such as an arm mount incorporating Stillpoints or similar. Or built-into the arm itself. Heck, built in to the headshell!

Slightly different - the 4Point topology seems unique - what are its downsides?

What I wonder is how do you when listening -- especially with older tone arms -- how do you separate bearing chatter from tonearm resonances? Most of those old arms had multiple resonance points and rang like the proverbial Liberty bell. After all, look at all the variety of materials now used in manufacturing tonearm. From wood to aluminum to carbon fiber to resins to ??? I always wondered about the immunity of wooden arms to temperature and humidity.

For me anyway, it's been designers addressing the rigidity and resonance properties of the arm tube that has lead to the biggest advances in tonearm sound.

[MylesBAstor]

I wonder if unipivots track the inner most grooves better than traditional gimbal type bearing designs ? I hear very little treble dulling with Graham arms...my only unipivot experience. My Clearudio Universal arm (gimbal) from what I recall had noticeable inner groove treble dulling.

Were the arms the same length Christian?

[rockitman]

The CA is a 9" Arm, the Graham 10"

[Rob]

What I wonder is how do you when listening -- especially with older tone arms -- how do you separate bearing chatter from tonearm resonances? Most of those old arms had multiple resonance points and rang like the proverbial Liberty bell. After all, look at all the variety of materials now used in manufacturing tonearm. From wood to aluminum to carbon fiber to resins to ??? I always wondered about the immunity of wooden arms to temperature and humidity.

For me anyway, it's been designers addressing the rigidity and resonance properties of the arm tube that has lead to the biggest advances in tonearm sound.

you're raising a point I was going to make after reading some of the responses to this thread, how do you know when you hear bearing chatter? whatever the bearing is doing or not doing is transmitted back down the arm to the stylus, by then what is heard can be influenced by so many things happening at once (alignment issues, miss tracking, anti-skate and vector forces acting on the stylus, etc).

I don't know how other mfrs do it, but Schroder carbonizes his wood arm tubes with a chemical process so they no longer exhibit any organic characteristics. in other words, they are devoid of any influence by humidity and temperature.

Ah, yes...the Han Solo tonearm wand.

[MylesBAstor]

Petrified wood. 😉

[Joe Pittman]

how do you know when you hear bearing chatter? whatever the bearing is doing or not doing is transmitted back down the arm to the stylus, by then what is heard can be influenced by so many things happening at once (alignment issues, miss tracking, anti-skate and vector forces acting on the stylus, etc).

I agree Rob, so many variables. It's hard to pinpoint problem areas. My first experience with bearing chatter and bearing damage began with the Grace 707 arm in the 70's. The Grace was the hot ticket with the earliest iterations of the Linn LP 12. I used the Supex cartridge with it which dumped a lot of energy into the arm. This was the beginning of "Loss of Information" era discussed by Ivor who advocated cranking down the cartridge at the headshell and keeping everything in the vibration path tight. Looking closely at the Grace 707 needle bearings, you could see and feel the bearings were loose and easily damaged. A machinist friend of mine would remove the needle bearings and machine larger bearing pockets for me. I then installed precision radial ball bearings with adjustable preload, resulting in vastly improved sound quality. I conducted many experiments with the preload force and could hear the difference between no preload/loose bearing chatter to too-much, to just right. Years later I visited Linn's manufacturing facility in Scotland and observed how they adjusted their bearings for the Ekos using the swing test.

[MylesBAstor]

I agree Rob, so many variables. It's hard to pinpoint problem areas. My first experience with bearing chatter and bearing damage began with the Grace 707 arm in the 70's. The Grace was the hot ticket with the earliest iterations of the Linn LP 12. I used the Supex cartridge with it which dumped a lot of energy into the arm. This was the beginning of "Loss of Information" era discussed by Ivor who advocated cranking down the cartridge at the headshell and keeping everything in the vibration path tight. Looking closely at the Grace 707 needle bearings, you could see and feel the bearings were loose and easily damaged. A machinist friend of mine would remove the needle bearings and machine larger bearing pockets for me. I then installed precision radial ball bearings with adjustable preload, resulting in vastly improved sound quality. I conducted many experiments with the preload force and could hear the difference between no preload/loose bearing chatter to too-much, to just right. Years later I visited Linn's manufacturing facility in Scotland and observed how they adjusted their bearings for the Ekos using the swing test.

I had a Grace 707 on my LP12 back in the '80s. Bearings didn't last two years and threw the arm away. Speaking of preloading, I think the SAT allows for that with different cartridges. But it is as you said a double edged sword. You can optimize the sound but at the same time if not careful destroy the bearings.

[Steve Lefkowicz]

I'll bet a lot of us had a Grace 707 at some point! Had mine on a Rega 2. Not a good match for most MC cartridges. Mine worked well with various Grados.

[MylesBAstor]

Grace F9E here.

[Daudio]

Still have my Grace F9E
Hard to part with old cartridge friends.

[Guest]

you're raising a point I was going to make after reading some of the responses to this thread, how do you know when you hear bearing chatter? whatever the bearing is doing or not doing is transmitted back down the arm to the stylus, by then what is heard can be influenced by so many things happening at once (alignment issues, miss tracking, anti-skate and vector forces acting on the stylus, etc).

I don't know how other mfrs do it, but Schroder carbonizes his wood arm tubes with a chemical process so they no longer exhibit any organic characteristics. in other words, they are devoid of any influence by humidity and temperature.

Across chatter and resonances and the various methods of addressing these, what we're really trying to isolate is the signal. That would seem to involve expediting cartridge resonance out of the cartridge and preventing resonance outside the cartridge from entering it.

I wonder to what extent that various forms of mechanical jitter impact the ability of the arm to fix the cartridge in space and on the record, and the ability of the arm to allow the cartridge to move freely across the record. I could see where v. 'loose' arms such as the Grace 707 cited by Joe make this an issue.

All the various and exotic tonearm implementations - materials and topologies - appear a means to these ends. Or is there more? Getting the signal out of the generator undamaged and into the phono section?

[Rob]

IMO, the closest thing that comes to a jitter-less solution is Bill Firebaugh's well-tempered arm is it the best sounding arm I've ever owned? no. To Myles' point I also remain agnostic and take each tonearm design on its own merits.

[Joe Pittman]

Across chatter and resonances and the various methods of addressing these, what we're really trying to isolate is the signal. That would seem to involve expediting cartridge resonance out of the cartridge and preventing resonance outside the cartridge from entering it.

Yes. Well said.

I wonder to what extent that various forms of mechanical jitter impact the ability of the arm to fix the cartridge in space and on the record, and the ability of the arm to allow the cartridge to move freely across the record. I could see where v. 'loose' arms such as the Grace 707 cited by Joe make this an issue.

The arm needs to track the theoretical center of the groove. Any variation or relative motion from this "point in space" is distortion.

All the various and exotic tonearm implementations - materials and topologies - appear a means to these ends. Or is there more? Getting the signal out of the generator undamaged and into the phono section?

No, there is nothing more. The cartridge does not know the difference between the signal (groove modulations) and added vibrations. The objective is to eliminate all forms of distortion not part of the signal. Distortions and their causes are many.

[MylesBAstor]

Yes. Well said.



The arm needs to track the theoretical center of the groove. Any variation or relative motion from this "point in space" is distortion.



No, there is nothing more. The cartridge does not know the difference between the signal (groove modulations) and added vibrations. The objective is to eliminate all forms of distortion not part of the signal. Distortions and their causes are many.

Even the vibrations travelling up the cantilever and reflecting back down in a MC cartridge affect the sound. Hence the difference between say a MC and a strain gauge that has a digital like quietness.