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  • #46
    Originally posted by Joe Pittman View Post
    I'm just beginning to run-in my dual pivot on the JMW-12 3DR arm. So here are my initial thoughts. I think there are two main variables to the performance.

    First, the dual pivot point rubs against the polished plate resulting in friction similar to "stiction" in a radial ball bearing. The arm is constantly moving across the record and the dual pivot point scrubs the polished plate surface, this results in a very small loss of overtones, decay, and ultra small detail compared to the unipivot. To optimize performance, we want to reduce the friction as much as possible. To reduce friction, I think it is helpful to adjust the side weight so the dual pivot lifts off, then add just the smallest amount of down force to keep the dual pivot from lifting off during playback. I would like to see the set screw point have a super polished radial point or better yet an inset sapphire ball point.

    Second, the added "stiction" friction has a beneficial effect by increasing inertia for bass excursions, like adding more mass to the arm but not adding more mass to the arm. So there may be some trade-offs here. However, the bass is the foundation of the music, and having superior bass performance increases the realism of the playback over the entire frequency range. So far, this is an acceptable trade-off. Sort of like two steps forward and one step back resulting in a step forward. Much more listening and tweaking needed.

    I would like to see VPI drill and tap a hole in all new arms for the dual pivot and make it a standard design. Users could decide to use it or not and it would add little cost.
    This is interesting, Joe. Can you say more on the benefit of increased inertia for bass excursion? I'm guessing you mean excursion of the groove, perhaps the slightly wider groove of bass passages? Increased inertia, without really knowing anything about this, to me means a greater than earlier reluctance(?) or tendency to move. But with friction/stiction it would seem to be reluctance.(?) Is it a timing issue? Or... ? I'm obviously not a physics guy, so if its easier to point me at something to read, no problemo.

    Q2 - Although there is friction factor, why wouldn't another one of these be added to the other side of the arm as well?

    Comment


    • #47
      Originally posted by tima View Post

      This is interesting, Joe. Can you say more on the benefit of increased inertia for bass excursion? I'm guessing you mean excursion of the groove, perhaps the slightly wider groove of bass passages? Increased inertia, without really knowing anything about this, to me means a greater than earlier reluctance(?) or tendency to move. But with friction/stiction it would seem to be reluctance.(?) Is it a timing issue? Or... ? I'm obviously not a physics guy, so if its easier to point me at something to read, no problemo.

      Q2 - Although there is friction factor, why wouldn't another one of these be added to the other side of the arm as well?
      I should have said increased resistance to inertia.

      Phono cartridge tracking is a bit of an enigma wrapped in a conundrum. You want the cartridge to see infinite mass for ultimate bass but you want zero mass so the cartridge can move effortlessly across the record, up/down for warps and in/out for off center spindle hole and so on. You can't have both infinite mass and zero mass at the same time. It amazes me the LP sounds as good as it does.

      For every action, there is an equal and opposite reaction (Newton’s Third Law). When the groove wall pushes the stylus, the stylus wants to keep going in that direction due to inertia (1), much like the tail wagging the dog.

      The mass of the tonearm helps the cartridge to track the theoretical center of the groove, but because the tonearm does not have infinite mass, there is a limit to how much resistance to inertia it can have. And so, it never tracks the theoretical center of the groove modulations accurately. One way to increase resistance to inertia without increasing mass is to increase friction. It is this increased friction with the dual pivot which increases bass performance in my opinion, albeit with a reduction in performance in other areas. This is a trade-off issue requiring careful adjustment for optimum performance.

      As I understand it, the original purpose of dual pivot designs for uni-pivots was to eliminate wobble and fine-tune azimuth. The Spotheim SpJ tonearm incorporates a dual pivot with the ability to adjust the azimuth on the fly. Having used the Naim Aro uni-pivot long term, you can pinpoint the effects of uni-pivot wobble and grow to appreciate the stability of a highly rigid bearing design.

      I think that the VPI dual pivot helps their arms bridge the gap between the uni-pivot and rigid bearing with the best of both and minimal (or imperceptible) down side. Friend’s reaction while listening has been very favorable so far. If anything, the dual pivot is a pleasure to adjust and dial in azimuth.

      Having a second dual pivot would not be beneficial in my opinion.

      (1) Inertia is the resistance of any physical object to any change in its state of motion; this includes changes to its speed, direction, or state of rest. It is the tendency of objects to keep moving in a straight line at constant velocity.

      Comment


      • #48
        There is Bob Graham's approach and I think his explanation of neutral, etc. balance is a good read.

        Precision tonearms providing the absolute best performance from any turntable.
        Myles B. Astor, PhD, Administrator
        Senior Editor, Positive-Feedback.com
        ________________________________________

        -Magico S5 Mk.2 speakers with SPod feet
        -Goldmund Telos 280 stereo amp
        -Goldmund Mimesis 37S Nextgen preamplifier
        -Doshi V3.0 phonostage
        -VPI Vanquish direct-drive turntable
        -VPI 12-inch 3D Fat Boy dual pivot tonearm, VPI 12-inch 3D Fat Boy gimballed and SAT LM-12 arm
        -Lyra Atlas SL Lambda, Fuuga, vdh Colibri Master Signature, MutechHayabusa, MOFI Master Tracker, Sumiko Songbird cartridges
        -Technics RS1506 with Flux Magnetic heads, Doshi V3.0 tape stage (balanced)
        -Assorted cables including Transparent XL Gen. 5, Skogrand, Viero, Kubala-Sosna, Audience Au24SX, Genesis Advanced Technologies and Ensemble Power Cords
        -Accessories including Stillpoint Aperture panels, Cathedral Sound panels, Furutech NCF Nano AC receptacles; Silver Circle Tchaik 6 PLC, Symposium ISIS and SRA Craz racks, Audiodharma Cable Cooker, Symposium Ultra and assorted SRA platforms.

        Comment


        • rockitman
          rockitman commented
          Editing a comment
          Indeed. To me, the best unipivot implementation in theory as I haven't messed around with other unipivots. If what he says is true...I'm a happy camper. I have little interest trying other ams...especially with the convenience of VTA adjustment predictably for every record thickness on the fly...no guess work with a calibrated spirit level on the pivot tower.

      • #49
        Originally posted by MylesBAstor View Post

        I think one advantage is the weight of the new hardware is enough to tip the arm to the side. Thus you don't have to mess around with twisting the CW and affecting the tracking force. You can also twist the CW too far and the sound becomes horrible.
        OK, Myles, I was hearing some edginess and twisted the CW back in and that sounds better. Better bass and more dynamic. Mea culpa.

        Comment


        • MylesBAstor
          MylesBAstor commented
          Editing a comment
          Exactly what I heard if the CW was twisted too much. Top end among other things becomes unlistenable.

          That's okay. I think it's good to try and figure out why we hear different things in a system or product. That's why it is important to talk about what recordings are used for evaluation too. We won't always agree but it's good to eliminate all variables first. It's also educational to listen to what other people's reactions are and see if you missed that aspect.

      • #50
        Originally posted by Joe Pittman View Post

        I should have said increased resistance to inertia.

        Phono cartridge tracking is a bit of an enigma wrapped in a conundrum. You want the cartridge to see infinite mass for ultimate bass but you want zero mass so the cartridge can move effortlessly across the record, up/down for warps and in/out for off center spindle hole and so on. You can't have both infinite mass and zero mass at the same time. It amazes me the LP sounds as good as it does.

        For every action, there is an equal and opposite reaction (Newton’s Third Law). When the groove wall pushes the stylus, the stylus wants to keep going in that direction due to inertia (1), much like the tail wagging the dog.

        The mass of the tonearm helps the cartridge to track the theoretical center of the groove, but because the tonearm does not have infinite mass, there is a limit to how much resistance to inertia it can have. And so, it never tracks the theoretical center of the groove modulations accurately. One way to increase resistance to inertia without increasing mass is to increase friction. It is this increased friction with the dual pivot which increases bass performance in my opinion, albeit with a reduction in performance in other areas. This is a trade-off issue requiring careful adjustment for optimum performance.

        As I understand it, the original purpose of dual pivot designs for uni-pivots was to eliminate wobble and fine-tune azimuth. The Spotheim SpJ tonearm incorporates a dual pivot with the ability to adjust the azimuth on the fly. Having used the Naim Aro uni-pivot long term, you can pinpoint the effects of uni-pivot wobble and grow to appreciate the stability of a highly rigid bearing design.

        I think that the VPI dual pivot helps their arms bridge the gap between the uni-pivot and rigid bearing with the best of both and minimal (or imperceptible) down side. Friend’s reaction while listening has been very favorable so far. If anything, the dual pivot is a pleasure to adjust and dial in azimuth.

        Having a second dual pivot would not be beneficial in my opinion.

        (1) Inertia is the resistance of any physical object to any change in its state of motion; this includes changes to its speed, direction, or state of rest. It is the tendency of objects to keep moving in a straight line at constant velocity.
        Thanks for taking the time for your response. With my limited understanding, "increased resistance to inertia" now makes sense vs "increased inertia". A force (friction) reduces (slows) the tendency of the stylus to shoot off at an angle that otherwise would carry it outside the groove, or at least the groove center. Then boom an instant latter it happens again. (Thus leading to the tangential tracking arm where increased resistance to inertia is not disireable. ;->) I'm still not sure about the impact on a particular frequency range, but better grasp your theory on why the dual pivot is effective. Kinda fascinating that it appeals based on increasing ergonomic feel, but its real stability benefit happens at an entirely different level. Again, thanks for the write-up.

        Comment


        • #51
          "when twisting the CW"...you mean turning the counterweight about its axis I presume.... that is changing the azimuth - no? When I get my kit, I will attach it without the 2nd pivot touching at all - then screwing it to just touch after my work with the Fozgometer to provide the proper azimuth. That being said...just wondering if anti-skate is affected due to the (even very slight friction of that 2nd pivot).....or is there a force similar to damping involved? The end result is the improvement in sound if any or the reduction of sound quality if any which makes these issues just "interesting".

          and then there is the question of how much pressure should be applied to that second pivot while maintaining the proper azimuth
          Last edited by Stringreen; 04-27-2017, 11:57 AM. Reason: additional thought

          Comment


          • #52
            Originally posted by Stringreen View Post
            "when twisting the CW"...you mean turning the counterweight about its axis I presume.... that is changing the azimuth - no? When I get my kit, I will attach it without the 2nd pivot touching at all - then screwing it to just touch after my work with the Fozgometer to provide the proper azimuth. That being said...just wondering if anti-skate is affected due to the (even very slight friction of that 2nd pivot).....or is there a force similar to damping involved? The end result is the improvement in sound if any or the reduction of sound quality if any which makes these issues just "interesting".

            and then there is the question of how much pressure should be applied to that second pivot while maintaining the proper azimuth
            Yes.

            Adding the dual pivot should give enough downforce to contact the thrust pad. Twisting doesn't necessarily change the azimuth if the screw contacts the thrust pad.

            If you have to add more downforce, twist the CW clockwise. As little as possible.
            Myles B. Astor, PhD, Administrator
            Senior Editor, Positive-Feedback.com
            ________________________________________

            -Magico S5 Mk.2 speakers with SPod feet
            -Goldmund Telos 280 stereo amp
            -Goldmund Mimesis 37S Nextgen preamplifier
            -Doshi V3.0 phonostage
            -VPI Vanquish direct-drive turntable
            -VPI 12-inch 3D Fat Boy dual pivot tonearm, VPI 12-inch 3D Fat Boy gimballed and SAT LM-12 arm
            -Lyra Atlas SL Lambda, Fuuga, vdh Colibri Master Signature, MutechHayabusa, MOFI Master Tracker, Sumiko Songbird cartridges
            -Technics RS1506 with Flux Magnetic heads, Doshi V3.0 tape stage (balanced)
            -Assorted cables including Transparent XL Gen. 5, Skogrand, Viero, Kubala-Sosna, Audience Au24SX, Genesis Advanced Technologies and Ensemble Power Cords
            -Accessories including Stillpoint Aperture panels, Cathedral Sound panels, Furutech NCF Nano AC receptacles; Silver Circle Tchaik 6 PLC, Symposium ISIS and SRA Craz racks, Audiodharma Cable Cooker, Symposium Ultra and assorted SRA platforms.

            Comment


            • #53
              Myles - I questioned VPI about the original set up instructions of the dual pivot which were as you know incomplete.

              Last time I will beat this dying horse....I have not seen an update (other than BRF's commentary on the subject) but at the time I was expecting to see a template or something marking a precise location for the new dual pivot. I was thinking that there would only be one "correct" location where the tonearm would behave properly with a second pivot point. Someone stated that my thought was correct if it was a true dual pivot geometry. Later it was stated that this mod is more of a stabilizing outrigger and that precision was not critically important. This is exemplified by the possible fore or aft mounting of the dual pivot. That said, every picture I have seen of the dual pivot installed by Harry / VPI has the pivot mounted aft of the left side counterweight ( possibly closer to that perfect position?). I am still a little bit troubled about the location of the pivot.

              In theory, If there is a perfect location for the 2nd pivot where any movement of the arm / cantilever up of down would result in the stylus remaining perfectly vertical, isn't the following true?

              Any position forward or aft of this theoretical perfect position for a 2nd pivot will result in the stylus leaning to the right or left about the primary axis if the second pivot remains in contact with the plate and the arm moves up and down (thus affecting the azimuth).

              In the real world, maybe these small maybe even tiny axial movements are irrelevant?


              Would you please add your thoughts to this discussion and let us know if you have experienced any strange behavior with a warped record (assuming that you have one)....This is all academic as I have no warped records of course...Just Kidding
              Last edited by Letsmakeadeal; 05-01-2017, 04:29 PM.
              Primary 2 channel stuff: Atma-Sphere MP-1 Mk 3.3, Pass Labs X600.5 amps, Aerial SW 12 subs, True Sound Works Ultimate Apogee Divas, Dunlavy SC4s, VPI HRX Reference w Avenger mag drive and Reference footers, Gimbal Fatboy, Yamaha GT2000 for Mono, Miyajima Kansui, Miyajima ZERO, Fidelity Research MC-201 & 202, VPI ADS, Vendetta Research SCP-1, Audio Note UK- 3.1X II balanced DAC, Meridian Sooloos, Western Electric Speaker wire, mostly diy balanced interconnects, Furutech Power Cords

              Comment


              • #54
                I've had no problem playing warped records with the dual pivot mod installed. So far, they've tracked more solidly than without the mod and they sound fine. I'm sure it doesn't hurt that I also use the outer ring.
                Analog: Forsell Air Reference, Transfiguration Proteus; VPI Prime Signature, VdH Crimson XGW, Transfiguration Phoenix S, VAS Nova Mono;
                Unmounted: VAS Nova Signature, Symphonic Line RG-8

                Digital: Mac mini 6,2 with YFS PS-12M LPS; Exogal Comet Plus, Exogal Ion PowerDAC
                Electronics: Aurorasound Vida, Channel D Lino C; Merrill Cara, Gryphon XT MC; Merrill Thor, Gryphon M-100 Mkii
                Cables: Morrow, Gryphon interconnects; YFS USB cable; Morrow, XLO, Channel D phono cables; Gryphon speaker cables

                Comment


                • mep
                  mep commented
                  Editing a comment
                  Warped records either need to go in the oven or in the trash.

                • rockitman
                  rockitman commented
                  Editing a comment
                  ^^^no they don't if you have an outer ring or vacuum hold down on the TT.

              • #55
                Originally posted by Letsmakeadeal View Post
                Myles - I questioned VPI about the original set up instructions of the dual pivot which were as you know incomplete.

                Last time I will beat this dying horse....I have not seen an update (other than BRF's commentary on the subject) but at the time I was expecting to see a template or something marking a precise location for the new dual pivot. I was thinking that there would only be one "correct" location where the tonearm would behave properly with a second pivot point. Someone stated that my thought was correct if it was a true dual pivot geometry. Later it was stated that this mod is more of a stabilizing outrigger and that precision was not critically important. This is exemplified by the possible fore or aft mounting of the dual pivot. That said, every picture I have seen of the dual pivot installed by VPI has the pivot mounted aft of the left side counterweight ( possibly closer to that perfect position?). I am still a little bit troubled about the location of the pivot.

                In theory, If there is a perfect location for the 2nd pivot where any movement of the arm / cantilever up of down would result in the stylus remaining perfectly vertical, isn't the following true?

                Any position forward or aft of this theoretical perfect position for a 2nd pivot will result in the stylus leaning to the right or left about the primary axis if the second pivot remains in contact with the plate and the arm moves up and down (thus affecting the azimuth).

                In the real world, maybe these small maybe even tiny axial movements are irrelevant?


                Would you please add your thoughts to this discussion and let us know if you have experienced any strange behavior with a warped record (assuming that you have one)....This is all academic as I have no warped records of course...Just Kidding
                I don't think I'm the right person to ask. The outer ring clamp pretty much takes care of most record warp and I haven't had any issues.

                You lost me a little on your first question. It seems to me that the azimuth should be constant as long as the second pivot is in contact with the thrust pad. Why should it be any different than with a unipivot? Or even less of an issue?
                Myles B. Astor, PhD, Administrator
                Senior Editor, Positive-Feedback.com
                ________________________________________

                -Magico S5 Mk.2 speakers with SPod feet
                -Goldmund Telos 280 stereo amp
                -Goldmund Mimesis 37S Nextgen preamplifier
                -Doshi V3.0 phonostage
                -VPI Vanquish direct-drive turntable
                -VPI 12-inch 3D Fat Boy dual pivot tonearm, VPI 12-inch 3D Fat Boy gimballed and SAT LM-12 arm
                -Lyra Atlas SL Lambda, Fuuga, vdh Colibri Master Signature, MutechHayabusa, MOFI Master Tracker, Sumiko Songbird cartridges
                -Technics RS1506 with Flux Magnetic heads, Doshi V3.0 tape stage (balanced)
                -Assorted cables including Transparent XL Gen. 5, Skogrand, Viero, Kubala-Sosna, Audience Au24SX, Genesis Advanced Technologies and Ensemble Power Cords
                -Accessories including Stillpoint Aperture panels, Cathedral Sound panels, Furutech NCF Nano AC receptacles; Silver Circle Tchaik 6 PLC, Symposium ISIS and SRA Craz racks, Audiodharma Cable Cooker, Symposium Ultra and assorted SRA platforms.

                Comment


                • #56
                  Thanks Myles - I totally agree with you that if the record is flat (as most are) then is doesn't matter. Everything stays square as we want. But visualize what happens in our imperfect world if the record is not flat and we aren't using the outer ring clamp. If the 2nd pivot is in front of or behind the primary axis of the arms pivot (up or down) and the arm is forced to keep that 2nd point grounded to the plate. When the arm moves up and down, wouldn't it cause the arm to twist right or left slightly depending on whether the 2nd pivot is in front of or behind the "perfect" location?

                  Anyway, everyone so far seems very happy with the mod...If anyone out there (smarter that I) can calculate where that "perfect" 2nd pivot belongs I will be very appreciative...My guess is that it is somewhere close to where Harry is mounting the pivot just behind the left counterweight....


                  BRF just posted this on the VPI forum which shows what I am talking about....

                  The rationale for the dual point location has been discussed previously. http://www.vpiforum.com/viewtopic.ph...=offset#p33222

                  Primary 2 channel stuff: Atma-Sphere MP-1 Mk 3.3, Pass Labs X600.5 amps, Aerial SW 12 subs, True Sound Works Ultimate Apogee Divas, Dunlavy SC4s, VPI HRX Reference w Avenger mag drive and Reference footers, Gimbal Fatboy, Yamaha GT2000 for Mono, Miyajima Kansui, Miyajima ZERO, Fidelity Research MC-201 & 202, VPI ADS, Vendetta Research SCP-1, Audio Note UK- 3.1X II balanced DAC, Meridian Sooloos, Western Electric Speaker wire, mostly diy balanced interconnects, Furutech Power Cords

                  Comment


                  • #57
                    The second pivot goes behind the left side side weight so it approximates the vertical motion of an offset gimbal and will not rotate the stylus azimuth on record warps. You should use minimal pressure on that second pivot, just enough to keep it engaged, and you will be set. The second pivot adds stability to the soundstage, tightens up the bass by giving the stylus more effective mass to work against, and for many of my customers makes the arm usable again when they develop mild tremors. All in all a win in all directions.

                    BTW, you can decrease tracking force at least 5% and get the same tracking ability. I now track the Atlas at 1.6 grams, and may go lower, with no issues at all.

                    HW

                    Comment


                    • #58
                      I just installed the kit and my main pivot point was such that the second pivot would need to just barely poke out of the mechanism otherwise azimuth would be off. This left the screw wobbly and it would unscrew itself after 2 records to the point where it no longer made contact. I want to raise the height of the pivot point. I have a 3d arm 10.5, and the nut under the dogleg. I used the set screw to raise the pivot 1/4 inch which seems to have helped by allowing more of the screw to be exposed . I have a 3d arm and there seems to be no way to change the pivot point on top of the bell. The way I did it does not seem to be the correct way though. Help

                      Comment


                      • #59
                        Originally posted by Harry Weisfeld View Post
                        The second pivot goes behind the left side side weight so it approximates the vertical motion of an offset gimbal and will not rotate the stylus azimuth on record warps. You should use minimal pressure on that second pivot, just enough to keep it engaged, and you will be set. The second pivot adds stability to the soundstage, tightens up the bass by giving the stylus more effective mass to work against, and for many of my customers makes the arm usable again when they develop mild tremors. All in all a win in all directions.

                        BTW, you can decrease tracking force at least 5% and get the same tracking ability. I now track the Atlas at 1.6 grams, and may go lower, with no issues at all.

                        HW
                        I thought the coils were were designed to align at a specific vtf, what benefit does the lighter weight get you?

                        Jeff

                        Comment


                        • #60
                          Jeff
                          In the 3D arm there is a small hole directly over the pivot point into which a hex wrench will fit allowing adjustment of the female bearing cup up or down. You may have to remove the small black cap which just pulls out rather easily...I don't remember the exact size but it is rather easy to determine by trial and error. Also on my new arms the pivot point itself is adjustable up or down so you may have a couple of options to raise the pivot point. You will also probably have to readjust your cueing mechanism.
                          Primary 2 channel stuff: Atma-Sphere MP-1 Mk 3.3, Pass Labs X600.5 amps, Aerial SW 12 subs, True Sound Works Ultimate Apogee Divas, Dunlavy SC4s, VPI HRX Reference w Avenger mag drive and Reference footers, Gimbal Fatboy, Yamaha GT2000 for Mono, Miyajima Kansui, Miyajima ZERO, Fidelity Research MC-201 & 202, VPI ADS, Vendetta Research SCP-1, Audio Note UK- 3.1X II balanced DAC, Meridian Sooloos, Western Electric Speaker wire, mostly diy balanced interconnects, Furutech Power Cords

                          Comment

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