Gimbal vs unipivot tonearms


Curious as to the difference between these types of arms. In my experience, it seems as if unipivots are much more difficult to handle.

Is it like typical debates - depends on the actual product design/build or is one better sounding or less expensive or harder to set up....?
sokogear
@mijostyn- "By all means get yourself a bigger room:-)"

       Actually: the property values have skyrocketed, in my neighborhood, as have the property TAXES, of course and I have a buddy in the realtor biz, who's going to list mine.

        How I wish country churches and old Amish barns hadn't become so popular to renovate into homes, in the last couple decades.

                            Anyway: I AM working on that!
@mijostyn- If you still have that TacT, DAC output board: chances are 99 out of 100; it was one of the surface mount caps, that went South.  It's
that exact failure, those in the know about Tact, check first.

      It was when one of mine did the same thing, that I decided to do the Full Monty and replaced all of those little punks, wherever I found them.

      That's been quite a few years and zero problems, since!

       I'd bet: were you test the caps on that board, find the culprit and replace it: it would come back to life.   Not that reading surface mounts on the board, is any kind of picnic, but...

        How I WISH this digital stuff were built point to point!   However: I suppose that would take cabinetry, the size of a small refrigerator and the same amount of cooling.

        OH: I'd also put money on you forgetting about that $10K Amethyst, were you to try the upgrade.

         If you're still using the Tact for anything: you could try a higher wattage Means Well very cheaply, to see if you notice any improvement, in it's dynamics and headroom*.       Everything just plugs in and you trim the voltages.

                      *Ever over-drive yours (digital clipping)?
@rodman99999 , Thanx for the info. I really like the Tact 2.2x. I love the dynamic loudness function  but, time and tech moves on and I am debating going for a Trinnov Amethyst. If I decide not I will look into upgrading the power supply. I had analog input boards but the right channel went south so I got a Benchmark ADC 1 with which I am very happy. Using outboard DACs gets complicated when needing four channels. Fortunately, the Tact DACs are excellent with a signal to noise ratio of 125 dB. By all means get yourself a bigger room:-)

@lewm , I can't think of any air bearing arms back then. I was not impressed with the Goldmond. I thought it a big waste of money. It was on the right path but the tech to pull it off was not available back then Rabco or not. It is now but at stupid expense given the demand. There is a German company making a belt driven carriage drive straight line tracker whose error is vanishingly low and the actual arm is a rather standard 2 axis affair. Horizontal and vertical effective masses are close unlike an air bearing arm. I'm sure it performs well but it is over $100K. The Schroder LT is a far better solution using the energy supplied by friction to power the arm. You should download the patent. It is the only way you can really understand what he designed. Reed did the same thing with the 5T but used a very low speed motor to power it costing twice as much as the LT.
The CB is a great design but the LT is brilliant. 

Air bearing arms and Clearaudio's design are defective from the start. They oscillate horizontally at low frequencies. Maybe you could dampen this out somehow but I have not seen anyone do this effectively. The suspended stylus has to move this mass along one way or the other, frictionless bearing and all. Swirling air currents around a cartridge are not a good idea either. 

GO MAX!!! 
Dear @dover  : ""  do not understand the trade offs inherent in each of the various options. ""

Agree but when you have to choose in between you will choose according what those trade-offs tells you and the ones that goes in better way to your specific MUSIC/audio priorities.

Like you Ihave first hand experiences with all that kind of tonearms you name it ( I owned the ET2. ) and my final choice is to gimball pivoted ones not unipivots or LT.
For me the gimball ones are way better than unipivots and this does not means I don't understand about trade-offs because I do.

R.
@daveyf 

@mijostyn  Air bearing arms are not worth talking about?? I wouldn't state that to any of the many owners of the Eminent Tech arm...an arm that I still feel can compete with some of the best available today.

Agree - and despite the high effective horizontal mass I ran a high compiance Shure V15Vmr in my ET2 for 10 years non stop ( with the stabiliser brush removed ), and the original cantilever was still straight as a die after all that time.

Unipivots ironically have the most rigid and free bearing due to the single point.

Gimbal bearings have much higher stiction than unipivots but are more stable.

I have all three arm types - gimbal, unipivot & tangential air bearing.
At the end of the day there are pros and cons with each type, and those that argue one over the other as an absolute do not understand the trade offs inherent in each of the various options.
@mijostyn- "What makes you believe the Tact does not go below 20 Hz?"

    I MEANT* to say: I cut off at 20Hz, in the program.   

    Lower would be a waste of of amplifier power, in my current room, given the dimensions and my phono pre has a subsonic filter, that can't (easily) be defeated.    It's 6dB/oct, so: affects freqs, somewhat higher than a steeper slope would.    

     Kinda between a rock and a hard place, though: if I ever have a larger space, I'm certain to address the issue.

                             *A consequence of Old-Timer's Disease and a brain-fart!

  



    

@mijostyn  Air bearing arms are not worth talking about?? I wouldn't state that to any of the many owners of the Eminent Tech arm...an arm that I still feel can compete with some of the best available today.

@rauliruegas -        I understand, perfectly!

      "Curiosity" has killed this old cat's wallet, many times over, in as many scenarios.

                                 "Not any more"...INDEED!
Mijo, the Goldmund T3F LT tonearm was a straight up ripoff of the Rabco SL8E, which was designed by an engineer who lived here in bethesda, MD, not a gnome in Switzerland. I always wondered whether it was done under a contractual agreement, and if not, whether there was a resulting law suit. Both of those tonearms  would have been prone to generate noise, and neither of them was a true linear tracker, because the action of the tonearm depends upon the stylus inscribing a tiny arc which then activates a switch which then turns on a motor that moves the pivot end of the arm wand down its track. Back in their day at one time or another I heard both, and I actually did not perceive any issues, but the demonstrations were usually in audio salons under poor conditions for critical listening. You are old enough to have heard them as well. Did you really like them in comparison to a good air bearing linear tracking tonearm? I never made that comparison myself.
Dear @rodman99999  :  Very appreciated your time and advise.

Now, The time when I was willing to buy almost every vintage/today tonearms was many years ago when I was in that " score " of my audio life and I owned 25-30 different tonearms and from that came my " curiosity " to try the Magnepan. 

Not any more but thank's.

R.
@mijostyn-   If you're still using the TacT; have you upgraded the power supply?   If not: get the highest (Watts) output supply that Mean Well now offers (I haven't kept up with their offerings, of late), replace the regulator with something better, like either Bellesons or NewClassDs and every electrolytic, with Sanyo OsCons.  

                                         The stock/OEM board:

                     https://www.mouser.com/ProductDetail/MEAN-WELL/PT-65B?qs=pqZ7J9Gt%2FmrUvp2%252BT2RNJA%3D%3D

     If you're using analog I/O boards; replace every one of the crappy, surface-mount, electrolytics, with Elna Silmic IIs and the regulators with the same as mentioned above.

     The Elnas are considerably bigger than the surface mounts, so: you have to be creative, with SOME of the larger values' positioning, on the boards.

      Parts Connexion has everything needed, to perform the above.  

Getting the leads soldered to the tiny pads, left when removing the old caps, and you want them short as possible, as I did, is quite the chore.

  Should you choose to undertake an upgrade, if your haven't already, I'd happily walk you through it.

   This isn't just a, "trust me" issue!      YOU WILL be amazed at the transformation, such an, "upgrade" (in this case: a VERY apropos term) makes.

    " The Tact does not allow you to see the system's frequency response after correction."

     I have a Behringer DEQ2496, left over from a pro installation and in a closet, that I use SOLELY (if you get my drift), for it's 1/3 octave Spectrum Analyzer.    That works quite well, in conjunction with the afore mentioned test LP.

                                    I use my ears from there.

                                          Happy listening!
@lewm , It is due to be in production mid July. They have their entire crew back now so it should speed up. I have the arm and all the cartridge mounting plates (various weights). The Smartractor is on standby. 

@rodman99999 , Son of a Gun, another Tact user. I used an LP 1 for 4 years on RH Labs subwoofers, a landmark product. The Tact is so superior in regards to bass management you can't compare them, not fair. What makes you believe the Tact does not go below 20 Hz? My 2.2X goes down to but not including Zero. Get one of these https://www.parts-express.com/Dayton-Audio-OmniMic-V2-Acoustic-Measurement-System-390-792 You will be amazed. You can then create individual target curves for each channel so they match perfectly. The Tact does not allow you to see the system's frequency response after correction. You will not believe how your image will snap into place.
I have used every type of tonearm known to man except the Schroder LT which I am dying to try. The best tonearm you can buy at this time other than the LT is an intermediate mass, two axis, 9 inch arm. The advantages outweigh the greater tracking error. My experience and test results measuring distortion by oscilloscope bear this out.  Theoretically a lighter arm with a high compliance cartridge should have lower distortion but the problem becomes making the arm stiff enough to dampen all resonance in the audio band. None of the ultra light arms have been stiff enough not to mention that it seems the day of very highly compliant cartridges is over. vinylzone is a typical example.
@daveyf , air bearing arms are not worth talking about especially with the Schroder LT available. They are a defective design right from the start. The only way to make a straight line tracker is with an animated carriage like the original Goldmund turntable. But that is a crazy expensive and complicated thing to do and maintain. None of these tables survived. I think the B+O was the most successful but, it sold to a different audience. Audiophiles have to be able to tinker. This is one of the reasons turntables survive. Digital is no fun! Tinkering with the B+O was impossible. 
Sorry to everyone for my error about the SME arm.

It's in a box downstairs, I thought I had sold it, now I remember that knife edge, thanks for correcting me. 

What I wanted to say, is

there is a difference between seeing the parts, knowing gravity has been equalized (as you do with the SME)

and trusting that it has been i.e. quality of my Gimbal's machining/parts, and the resulting 'equalization' of forces/freedom of movement.

and trusting unseen parts, like my Acos Lustre GST 801's internal magnets.

The methods of retaining settings, again like the SME, can give great confidence, or, like my Acos, requires 'belief' after setup.

I rarely checked my SME after setup; I often check my Acos's unseen magnets. 


@rauliruegas -   Coincidentally: the same day I mentioned what the Magnepan arm typically brings, over there: this popped up on eBay:

     https://www.ebay.com/itm/194208016067?epid=1286459254&hash=item2d37b326c3:g:-pAAAOSwPO5Zz4kN

        Note the missing Anti Skate bucket.    Kinda important and hard to fix, or find!

        If you're sincere, regarding your desire to actually listen to and test one; this is available at a slight uptick over what they sold for new:

     https://www.ebay.com/itm/164781914680?hash=item265dc47a38:g:ejwAAOSw17dgXO20

          They mention taking offers, so...

          Of course: I'd be leery of that, "NOT TESTED"; given how delicate the arm wiring sometimes seemed, in these babies.   I bought a spare, complete arm & output cable, years ago, just in case.

          Deduct what the typical AR table brings these days, from what this seller anticipates getting for this combo (plus shipping):

     https://www.ebay.com/itm/143137393314?hash=item2153a74aa2:g:OwUAAOSwTmxcao05

           Some folks in this hobby seem rapacious to me, but then: there IS that supply & demand thing.

           Sorry if I'm getting tedious, but: as I mentioned: someone out there seems to agree with my assessment of the arm.

                                                    TRY IT: you might like it!  😉
                                    (second time I've ever used an emoji, in my life)

                                                           Enjoy the journey!

I am unsure if any of these tonearms would suit your particular turntable. However, based in the UK, I am using an Audio Origami PU7 on my Linn LP12. It tracks beautifully and sounds superb
Other mainstream arms in the UK that might be worth a look also are the Roksan Nima or Roksan Sara.
All depends upon budget and suitability of course.
With all due respect and appreciation for the knowledge and experience shared here, the inclusion of an Audiomachina V8 Broad-Spectrum Cartridge/Tonearm Vibration Absorber between the cartridge and tonearm will likely far surpass any difference between a well set up gimbal or unipivot tonearm.


I have a 3D on my Classic 3 Sig SE.
I’m one that tries to turn lemons into lemonade. After I had VPI get the S2P distance right and the addition of the dual pivot upgrade, I’m happy with it. In addition, what made the dual pivot much quieter, is my PEEK film upgrade.  Next is having it rewired with a continuous run of Audio Note silver.
@rauliruegas:     "You are rigth but the unipívot behavior is way similar in between this kind of design."

         I would never deny that fact, BUT: nor would I ever categorically state that the design could not function very well, if not excellently, if properly incorporated with an appropriate cart, base/suspension, etc.

          You mention having tried to purchase the Unitrac I, on eBay.    Obviously, then: you're familiar with what they can bring, even if just for parts.   Especially: in Japan

           Some out there appear to share my opinions, regarding the arm.

            "...you are happy and this is what it counts: rigth?"

            Whether when I had my business, the contract work afterward, or running sound for a band; the customer/musicians always got the sound signature that pleased THEM, whether I thought it sucked, or not.

            My philosophy, there: "The customer always thinks they're right!"

             Happily: the vast majority were open to learning and, subsequently, very pleased.
Dear @rodman99999  : "   ever having listened to or tested the other's system "

You are rigth but the unipívot behavior is way similar in between this kind of design. Never mind, you are happy and this is what it counts: rigth?

R.

@rauliruegas, et al:  I wish I could be surprised, by the marked propensity of so many on the 'GoN to assume and advise others; there has to something wrong with their system, without ever being within 100 Kilometers of same.
       
       Let alone: ever having listened to or tested the other's system.

      "I never can put my hands in a NOS Unitrac and the only time I was nearer to I losted on ebay auction, my lost because I wanted to test it."

       To be clear: are you admitting never having actually tested or auditioned the Unitrac I; with or without any of my previously mentioned cart choices?

        "Btw,my room/system is fine tunned through nearfield real MUSIC tracks LPs tests."

         AS IF: the cited test LP assuredly must be the only way I have fine-tuned MY room/system?    

          Never mind: over five decades of familiarity with the sound of the REAL thing, in a plethora of acoustic environments (good and bad/unplugged and reinforced), when on stage, in a sound booth, an audience and in live venues of my own design and/or recommendations?  

           NOT that I think I have it all together.   Something Feynman often mentioned, during his lectures, when fondly reminiscing about his father, "Never stop learning", (one of his rules of life) has always resonated within me.

                        However: I was NOT born yesterday!

           "...if you don't like it always can return to the Unitrac."

           I'm kinda one of those, "If it ain't broke: DON'T FIX IT" types.

           At the age of 74: I'm not inclined to kid myself about (what's left of) my aural acuity.    Yet my system still manages to amaze my few musician friends extant, as well as those new, I allow to visit my swirling vortex of entropy (read: pathetic, embarrassing abode).  

                   "...enjoy the MUSIC NOT DISTORTIONS"
 
                                  Trust me: I do TRY!

                      Happy listening and enjoy the journey!




Dear @rodman99999  :  I almost agree with all what you posted  ( only a couple of issues where I have a " different " opinion. ) and you are rigth.

I never can put my hands in a NOS Unitrac and the only time I was nearer to I losted on ebay auction, my lost because I wanted to test it.

Anyway,  the Unitrac shares the same " problems " not only as unipivots but gimball tonearms too and these is that develops several kinds of resonances during playback that the Unitrac can't avoid and does not matters that the cartridges been high compliance.
Unfortunatelly those developed  resonances/distortions just " colored " the top to bottom the frequency range of what our system is reproducing.

In that " top to bottom " the more important issue is to damp/tame those resonances precisely at the bass range because its harmonics affects all the frequency range. Gimball tonearms are superior to unipivots in this speciofic regards.

So, I'm with the @mijostyn advise that even that you are satisfied with what you have you need to make some listen sessions with a gimball tonearm. The overall improvement could be higher that what you can imagine and if you don't like it always can return to the Unitrac.

Btw,my room/system is fine tunned through nearfield real MUSIC tracks LPs tests.

Regards and ejoy the MUSIC NOT DISTORTIONS,
R.
         ps: Obvously, there's MUCH more to the faithful reproduction of Bass, via an arm/cart and system, than just a frequency response curve.  

         If it doesn't sound/feel/convey REAL (ie: clean/clear pitch, the tightness of the drum skins, definition between rhythm section instruments, ambience recovery, not to mention: the flutter of a slow Leslie horn or your pant legs and heart, during those pipe organ pedal notes), it ain't worth squat!

                                                    Enjoy the journey!
      When you guys run near-field response tests, that come back flat down to 20Hz, from stylus to woofers, get back to me.

              https://www.analogueseduction.net/test-records-turntable-set-up/elipsonlp.html      (see: B4 - B9)
 
      My TL woofer system, crossed in at 80Hz (10th Order, Butterworth), was designed for output down to 16Hz, by Roger Sanders, back in 1980.      Article: published in Speaker Builder magazine that year, along with two on building your own electrostatics.

       If interested: .https://cc-webshop.com/collections/speaker-builder-magazine/products/speaker-builder-the-lost-years-...

      My TacT RCS 2.2X's room correction program cuts things off, sadly, at 20Hz.     My Dahlquist DQ-LP1 (what I was using, back when I built the woofers, didn't and I had a much larger room, as well.    I know their and the rest of my system's, capabilities quite well and have been VERY happy (except for current room limitations).

       If I were going to change anything; it would be to a swarm woofer system, to overcome the present room.

        Glad you guys are enjoying your arm/cart combos.  

        I certainly have enjoyed mine, over the past forty years!

                                               Happy listening!
@rodman99999 

I've been using a Magnepan Unitrac I, since 1981.
I have one, and recently replaced it with a Rega RB300 finally rewired with Discovery wire.

I have it on a vintage Denon, and I always thought the lack of bass was due to the table. It wasn't, at least not all of it.

The Unitrac still does some things better than the Rega, but the bass is greatly improved. This is with medium to high compliance cartridges.
There is as much difference among different air bearing tonearms in terms of these same issues as there is between a Unipivot and a gimbal bearing pivoted tonearm. It would take a separate thread to sort that out.
IME all designs have their issues. The above mentioned Well Tempered ( which I own and very much like) has an issue with its adjustability and its front/back stability (although this has not proven to be a sonic detriment that I can hear). The unipivot and the gimbal have their pluses and minuses. I would think that a gimbal, if done well, would have superior stability to a uni pivot, all else being equal. Perhaps we should include an air-bearing design here as well....maybe best of all worlds?

Nothing like a big organ in a big space. The Royal Albert Hall comes to mind. When the 32 footers light up it is like the hand of god shaking you. Your vision blurs! Many of the largest organs in the world are here in the states. There is one in Rode Island and another in Philiderphia. West Point has a big one. 
I have not played an organ piece in a while and I have some great recordings. Unfortunately I still do not have a turntable and none of my organ records are digital files, all vinyl. 
You have to trust me on this one rodman99999, your bass can be even better!
@mijostyn-    I've never had a problem getting excellent Bass with my chosen carts.

       Always have tried to match them correctly (compliance/effective mass, within reason), which, I realize, some think is bunk.

        In my mind: a high compliance cart, in some of the newer, higher mass arms, would create other problems.    ie: exaggerated cone motion, when trying to ride record warp, possibly: early compliance collapse and excessive stylus wear?

        Anyway: I've always been a Pipe Organ-phile, Bass lover and got acquainted with the sound of, "live", way before ever owning a system (Elementary School music classes, etc).      Well- there was the turntable and Elvis 45's, at around the age of 12, but...

       Two of my all-time favorite vinyls are the Crystal Clear, Direct to Disc, of Virgil Fox (The Fox Touch, Vol I) and MFSL, Dark Side of the Moon.

        Toccata and Fugue in D minor and the heartbeats (not to mention the rest of that disc), both are mesmerizing, when reproduced correctly.

                             Thanks for the suggestion, though!
@lewm , that is pretty bad. Hopefully, they replaced all of them. It is all right to make a mistake. It is what you do about it that counts. 

sokogear, I agree, Rega arms are a great value. Origin Live arms are better but a lot more expensive when you get up to the good ones in their line. At the bottom I do not think they are any better than the Regas.

@rodman99999 , I think you are right. If you have a unipivot it is best to stick to highly compliant cartridges. I also think you would be amazed at the improvement in your bass if you got yourself a new arm. If you are after better sound it always helps if you can identify problems with easy fixes:-)
Mijo, As I recall, the early 3D tonearms from VPI were warping at temperatures where a $4K tonearm, or any tonearm, should not warp.  Like temps reached during shipment or on a very warm day in a non-air conditioned environment.  But they did fix the problem, so far as I know.
      I've been using a Magnepan Unitrac I, since 1981.

      A very low effective mass unipivot, that I've always used with fairly high-compliance carts.  (ie: two Denon 103d's, Dynavector 17D3, Soundsmith Aida)

       It's my opinion: Physics would dictate, with a lower compliance cart, the stiffer suspension would tend to cause vibration migration, up the lightweight arm tube and resultant chatter in the unipivot.

                                           The thought makes my teeth hurt.

        Can't help but wonder, how many may have tried that and blamed the design?
You would think that 3D printing would be less expensive as there is very little labor involved. I think the other physical properties of the material they are using would be most important such a density, stiffness, resonance properties, etc. Anything can be damaged by heat if you crank up the temp enough. At any rate using a gimbal set up is a step in the right direction even if it is a plain Jane design. Tri-Planar, Schroder , Reed and Kuzma have all come up with beautiful and novel bearing topography. 
Could be (I wonder what material can go through a printer not subject to heat), but $4K is quite expensive compared to other options. Bottom line - if unipivot was the future, they wouldn't be going in another completely different direction.
In fairness to VPI, I think they long ago fixed the problem with warping of their 3-D tonearm due to heat. And the uniform 3-D structure is touted as an advantage, not a cheap shortcut as you imply.
I know VPI is now pushing gimbal arms, but they are WAY overpriced, and they are made on a 3D printer - I guess out or some kind of plastic, and I saw in a previous discussion that they actually bend sometimes during shipping if it gets hot, and they tell their customers to use a hair dryer to bend them back - I kid you not. They also say they'll replace them if you want. $4K to boot!

The unipivots that bounce around are definitely a PITA to use, set up, you name it. I hear they make nice tables though.....and they started out making bases for Denon tables.
Darn, I thought I was the only one who thought the VPI arm was trash.
fsonicsmith, you are stating opinion as fact. You can't do that because it freaks out a lot of insecure people. Don't do it again;-)
@rauliruegas , that is an insane video! What a great set up. He jury rigged the whole thing.
 It was not a unipivot arm but it was very interesting to see the torsional deflection when he skipped grooves.
At the end of the day a tonearm and cartridge in combination is ideally a pure vibration receiver. Every movement of the cantilever caused by its travel through the grooves is ideally converted to electrical signal unimpeded by the tonearm or any limitations of the cartridge. What happens when a cantilever is pushed laterally in one direction and another only damped by the underhung counterbalances employed by a typical unipivot? The answer is simple-vibrations are no longer being received intact and instead are compromised. And the grooves in which bass sounds are embedded cause the most lateral travel and are the most compromised. But then everything is likely compromised more than they have to be. The VPI unipivot design was very poor. So why be surprised that VPI is now slowly but surely converting to gimbal designs?
I might add that different arms behave differently.  Not all gimballed arms will be as good as the latest (last) Jelco, probable some better.  The JMW-12 arm is an early VPI design, much improved over the years but still better than many.
I lived with both gimballed and unipivot.  Own very good VPI JMW-12 arm, two arm tubes.  They are quite difficult to get "just right."  And I still found the sound a bit lacking.  The arm is on a VPI Aries Extended table.  No particular difference between the arm tubes.

Just for fun, I built an experimental table from early VPI TNT parts (platter, spindle, bearing, clamp, motor) and a Jelco TK-850L tonearm.  Paid attention to the details.  Using the same cartridge (Soundsmith rebuilt Clavis D.C), the difference was dramatic.  Better performance in every aspect of performance.  Setup was a breeze.  Thought it might be an anomaly, so I picked out a cartridge from "the drawer" (AT OC9/II). Same results.  

I can't say for sure it was ONLY the arm, but the performance with the table using the Jelco was  much better, particularly in bass control and depth, soundstage, image and subtle instrument nuance.   Mids and treble were very natural compared to the slightly etched JMW-12.  

I have subsequently migrated to a Lyra Skala on the home built table and Jelco arm,  There is no reason to consider an upgrade nor any performance deficiency I can detect.   


Both can be done well it is not going to make or break the table but what it more important is how the table as a whole sounds with the entire phono system cartridge, phono stage, and preamplifier, and amplifier involved on complex music. That is when you have found your correct analog rig.
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Dear @sokogear : "  they don't mention gimbal or unipivot in their Series V arm description.  ""

I think you are an analog newcomer .

This is the Agon ANALOG forum and other than the newcomers almost all are experienced hobbyst that know SME tonearm are not unipivot designs .

SME knows that's not need it to put in the tonearm description that's non unipivot design.

R.
Classic SME tonearms used a "knife-edge" bearing, which is definitely different from a unipivot but does allow for some "chatter".  Mijostyn mentioned this in responding to Elliot's erroneous suggestion that his older SME tonearm was a unipivot.  As I understand it, modern SME tonearms (like the IV and the V, maybe) have either done away with the knife-edge principle or have modified it to make it more stable, similar in philosophy to what Graham and Kuzma have done to stabilize the pivot bearing on tonearms that started out as unipivots.  I own a RS Labs RS-A1 tonearm that is a very crude unipivot, and 7 other tonearms that are gimbal type. Also, I used to own the British tonearm that used a mercury bath to establish electrical continuity between the arm wand and the base; I can't recall the brand name, but I am guessing Keith Monks.  With all its faults (and the danger of mercury exposure), that tonearm had a kind of airy quality that was pleasing.  So too does the RS Labs, which performs way above its very oddball design. However, I confess it is not in use at this time.