I Am Thinking I Really Like Uni-Pivot Arms

[Vintagear]

I was recently looking to buy a second turntable and for this one I specifically wanted to try a nice belt drive. I narrowed it down to two brands and for various reasons finally decided to go with VPI. The fact that I wanted to try their Uni-Pivot was one of the primary factors in my decision.

I'm glad I did...

 

[twiiii]

I still prefer linear arms, yes they have their own issues. But they don't skate across the grooves , don't need bias compensation, track at lighter pressures for the same or better tracking ability than pivoting arms and have semi automatic operation so you don't have to handle the wiggle fly away tone arm with. your arthritic fingers, that have lost the ability to feel as they once did. I have thought any number of times about getting a Aries IIID but with out the tome arm. The 10 inch model just scares me to death, plus I use MC cartridges and if I bend a cantilever the results are cheap.. I don't like the set up issues either. I guess I could sell one of my houses and buy a SAT arm, but lets get real. There isn't a lp out there that deserves spending that kindd of money. Same goes for the top of the Line Clear Audio Tables with the linear tone arm they produce..

 

[Muddywaters]

I've had a VPI 10/10.5 for almost 20 years. Once I got the teardrop weight life was easier setting it up. Next adding Peter Lederman's Soundsmith Counter Intuitive made small adjustments much simpler for azimuth and vtf. I've run many cartridges on them from Dyna 50X and 20X, XX2, FR MC201, ZYX Airy 3 and Grado Signatures even Denon 103's and a Decca Super Gold..

Only slight performance reduction I've noticed, which is cartridge dependent, was they can be a little bass shy. Not in extension but weight and harmonic richness of the bass. They are very detailed and good tracking arms. Also why they don't show up on the used market everyday.

 

[]eep]

Ain't lines geometry and pull physics? I know the geometry was 10th grade and the pull was statics and dynamics in college, engr courses.

No. I was referring to vector geometry, a geometrical model how to calculate the direction and strength of forces in a closed system. That means all forces balance each other. That is called statics, or part of it. With a ruler and angle bow you can easy draw it out.

Sorry if I don't know the correct terms but in Dutch the words and terms are all different. University is 30y ago.

 

[Blue Shadow]

No. I was referring to vector geometry, a geometrical model how to calculate the direction and strength of forces in a closed system. That means all forces balance each other. That is called statics, or part of it. With a ruler and angle bow you can easy draw it out.

Sorry if I don't know the correct terms but in Dutch the words and terms are all different. University is 30y ago.

That is why I mentioned statics, same college course. Heck if I had known it was just geometry, I would have done better in that class. Geometry was easy for me.

 

[]eep]

don't forget off-set. don't forget lateral balance.

edit: and apologies if this derails this thread, it's not my intent.

watch the arm skate hard right to the spindle area, with no stylus interaction with vinyl, or overhang, or etc etc etc.

Please disregard that YouTube Technics 'expert'... (sort of like an Apple 'genius'). If a tonearm is statically balanced perfectly it will not move in any direction. Even if it has close to no friction (like it should). You can put the turntable sideways and it still won't go anywhere. As any old Dual will prove. That video makes my toes curl.

What the guy in the video is doing is 'famous last words'. And showing that the 'bad tonearm' (ie bad and worse) has bearing friction or a stiff wire by putting tension on the anti-skating spring. He has no idea how much tension he puts on it since the dial only shows some inverted unrelated numbers. And replacing a tonearm costs less than 2h work. I guess he's severely overpaid.

Skating only happens when the vinyl touches the stylus, and because it spins at an angle (towards the spindle, caused by 'overhang') it drags it in that direction. If there's no contact there can't be any force acting on it. Unless you pull on it sideways like the 'expert' did with the anti-skating spring. Or a magnet (ooh, no contact! )

 

[ripblade]

not wanting to get away from Mr Pigs arm here............but looking at the front of an arm that is skating,........( 1 ) is the arm leading the stylus towards the spindle? ( 2 ) or is the stylus leading the arm towards the spindle?
the correct answer is #1. the arm is skating, not the stylus. The next correct answer is Physics.........the geometry explains why the physics (force vectors) are the answer.
Back to Mr Pigs personal findings on the arm. Wood is a very good tonearm material in keeping out odd harmonics from building across its length. Think of a bow for a violin or cello. A unipivot is an almost "infinite mass" at point of contact. That point of contact is almost not a boundary due to the almost infinite mass, meaning energy passes right through that boundary without much wave reflection at boundary. What wave reflection there is favors the second order harmonic.

we're celebrating 50 year anniversary of the moon landing. " we" understood geometry and physics pretty good 50 years ago using what came down to a basic calculator and pencil and paper. The turntable people 50 years ago had a pretty good understanding of how the things worked, or didn't . "New and improved" doesn't make everything else "old and lousy "

What would be your take on the physics behind the RS-A1? It looks to me like the inventer's intent is to reduce as many forces as possible acting on the cantilever (including scrubbing) except for VTF and the groove modulations. The underhang and zero offset I get; what I can't wrap my head head around is the freely swiveling shell...

 

[Tedrick]

I will agree with what others have posted in this thread about VPI unipivots. I own two, and once set up and azimuth is set, they stay set up and work beautifully. I've also noticed very little of the "unipivot wobble" that many seem to worry about.

Having said that, I've had a chance to install, setup, and listen to a Graham Phantom Elite unipivot. It is a beautifully engineered tonearm, and has the most elegant solution for adjusting azimuth that I've ever seen. The Phantom 'arms use a pair of opposing magnets instead of weights to adjust azimuth, and these magnets all but eliminate any chance of wobble during play. I would love to own a Phantom 'arm someday.

 

[marcmorin]

Skating only happens when the vinyl touches the stylus, and because it spins at an angle (towards the spindle, caused by 'overhang') it drags it in that direction. If there's no contact there can't be any force acting on it. Unless you pull on it sideways like the 'expert' did with the anti-skating spring. Or a magnet (ooh, no contact! )

an arm that is skating during play is leading the stylus towards the spindle. where the arm gets that energy to do so is from the LOSS of energy at the stylus due frictional forces ( static friction is higher than sliding friction) The universe hates a void......the drop in electromagnetic force (friction) has to be met with an equal gain in gravitational force.( torque) The offset vectors can be looked at as gradients. Gravity is pulling at those angles. which is the energy pulling the stylus to the spindle.

the reason the arm in the video did that is due to mass offset about the axis creates torque. torque has to follow the laws of gravity.

 

[marcmorin]

What would be your take on the physics behind the RS-A1? It looks to me like the inventer's intent is to reduce as many forces as possible acting on the cantilever (including scrubbing) except for VTF and the groove modulations. The underhang and zero offset I get; what I can't wrap my head head around is the freely swiveling shell...

the scrubbing of the stylus would have to be great. Scrubbing, or warp wow, goes up with the position of the pivot in relation to the vinyl surface. the higher the pivot fom vinyl surface the higher the warp wow

 

[]eep]

an arm that is skating during play is leading the stylus towards the spindle. where the arm gets that energy to do so is from the LOSS of energy at the stylus due frictional forces ( static friction is higher than sliding friction) The universe hates a void......the drop in electromagnetic force (friction) has to be met with an equal gain in gravitational force.( torque) The offset vectors can be looked at as gradients. Gravity is pulling at those angles. which is the energy pulling the stylus to the spindle.

the reason the arm in the video did that is due to mass offset about the axis creates torque. torque has to follow the laws of gravity.

Sometimes im pestered with bouts of humor bouncing around under my skullcap too. It's like a pinball machine in there you know. The more synapses the greater the number of bumpers and flippers and those twirly things... So you can imagine what happens when the ball tries to escape to the other half of my brain where it does all sorts of trajectory calculations to the other side where it's suddenly supposed to handle puns and wordplay and find Das richtige Lädchen pour faire des propere mots muy comedio and ineens grappig zijn.

If you're trying to be funny say so with a so everybody gets it... and skip the off-topic part.

 

[mkane]

way off topic here but I'll bet not many know who Jeep is.

 

[mkane]

 

[mkane]

I've had 2 VPI unipivots and their wobbly nature was not a bother at all.

 

[Grbluen]

way off topic here but I'll bet not many know who Jeep is.

I'll bite. Who is (s)he?

 

[mkane]

post #53

 

[ripblade]

the scrubbing of the stylus would have to be great. Scrubbing, or warp wow, goes up with the position of the pivot in relation to the vinyl surface. the higher the pivot fom vinyl surface the higher the warp wow

I think the idea is to have the wand fulcrum in line with the needle, as if the wand itself was an extension of the cantilever. This, in order to minimize the dynamic forces so as to reduce the need for static compensation, thus achieving greater equilibrium. In the case of large dynamic swings the increased resistance not only momentarily increases skating but also VTF, pulling the cantilever down and shifting the SRA towards the negative. Supposedly, the high pivot negates the effect of scrubbing, or at least the distortion created is less objectionable than that posed by a conventional parallel wand.

Audacious design, that's for certain, and goofy enough it just might work.

 

[]eep]

way off topic here but I'll bet not many know who Jeep is.

The friendly little creature with unsuspected superpowers from Popeye whom the Jeep vehicle was named after.

I don't want to be just off-topic so here goes

I think the idea is to have the wand fulcrum in line with the needle, as if the wand itself was an extension of the cantilever. This, in order to minimize the dynamic forces so as to reduce the need for static compensation, thus achieving greater equilibrium. In the case of large dynamic swings the increased resistance not only momentarily increases skating but also VTF, pulling the cantilever down and shifting the SRA towards the negative. Supposedly, the high pivot negates the effect of scrubbing, or at least the distortion created is less objectionable than that posed by a conventional parallel wand.

Audacious design, that's for certain, and goofy enough it just might work.

Maybe... But wouldn't the best position for the pivot point be in line with the lp surface? There the up and down movement would cause the least speed and height deviation. cos +/- 0.x° is less than cos (h°+/- 0.x°) where h is the angle bc of the height and 0.x is the wobble.

 

[Mister Pig]

So its been a few days since I got the Denon DL-S1 delivered, I installed it on Saturday as I recall. This is a very nice combination between arm and cartridge, with excellent detail. tonal balance, space, and dynamics. Just a great combination for not a terrible price.

The cartridge weighs 7 grams, and that is a bit chunkier than most cartridges this arm would normally be used with back in the day. So I am finding that I need additional side weight so I can get azimuth adjusted. That is a solution I need to work through.

Secondly, I think it might be a good idea to give the teak arm wand a bit of a rub down. I am not sure if I would use danish oil, tung oil, lemon oil, or another product. Anyone have any thoughts?

So far this combo shows a lot of promise.

Cheers
Mister Pig

 

[ripblade]

I'd use beeswax.