What is the fascination with an "S" shaped tonearm?

[marcmorin]

If their pivots and the stylus are not parallel, the stylus will see azimuth roll and they are hearing the roll on the warps.

Wayner

They will see it regardless of the bearing offset. put a bubble level on the headshell, raise and lower the arm. you will see the camber change.

 

[marcmorin]

Wait, that shouldn't matter because anything on the plane of a rotation will have the same kind of camber regardless the path to it. The angle is the same regardless the path to it. The only difference is if you have a long arm, you will have less of an angle when tracking a warped record vs a short arm.
so in that case there is no difference between the yaw angle on a straight or curved arm as long as the effective length is the same.

How in thee hekk can the cantilever point straight down if the arm is lifted or dropped below level when the cart is set at an offset? The only way it can is in a linear arm, no offset. only forward/back rake is affected

 

[WaynerN]

They will see it regardless of the bearing offset. put a bubble level on the headshell, raise and lower the arm. you will see the camber change.

I give up..............

 

[jomondz]

S shaped tonearm is darn sexy.

 

[ehoove]

Flame suit on - IMHO the only real advantage of an S arm is it is easier to change cartridges. A properly designed pivot straight arm will require no lateral balance adjustment. Materials, construction and bearing design are much more important than the straight vs. S versus J debate. A good arm is a good arm. Original SME is curved, the current ones are straight, and set up right work great. For the record, my arm is a damped unipivot straight arm (Audio and design - same as KMAL) I also have an old SME and think both are great. My 3 cents....

Edit: Slight back peddle. Unipivot arms are extremely sensitive to lateral balance, and AFAIK they are all straight with no detachable head shell. And require tweaking of the lateral balance. (the KMAL uses an eccentric counter weight.

The Magnapan Unitrac 1 has a detachable head shell. Great low mass arm BTW
Regards,
Jim

 

[ehoove]

I agree. S-arms, I know, are very popular on turntables made in the '70s. I don't recall many straight arms back then in my neck of the woods.

Thorens TP16 (I bought a TD125 MkII in 1972)
Regards,
Jim

 

[sregor]

I agree. S-arms, I know, are very popular on turntables made in the '70s. I don't recall many straight arms back then in my neck of the woods.

(dirty word alert) How about all the automatic turntables - Dual, Miracord, Garrard, BSR BIC. And a lot of tables besides Thorens. Lenco. B&O. Connoisseur.
S-shape arms in the 70's were predominately of Japanese manufacture.

 

[tubewade]

They will see it regardless of the bearing offset. put a bubble level on the headshell, raise and lower the arm. you will see the camber change.

I did it on my Linn, straight arm, and on my LAB-500, S-arm. The bubble goes straight forward and straight backward. No camber change. What are we missing here? Now on my Pioneer there is a huge camber change, but it does not use a bearing that is offset the same angle as the cartridge.

 

[jasonsong86]

How in thee hekk can the cantilever point straight down if the arm is lifted or dropped below level when the cart is set at an offset? The only way it can is in a linear arm, no offset. only forward/back rake is affected

Of course it will pitch at an angle when you lift it up the arm but someone said straight arm roll less than s-arm is not true. they both roll the same amount.

 

[VinylSoul]

Best way to eliminate azimuth error is to keep planes of bearings and headshell the same and adjust azimuth at the arm base like the wheaton tri-planar. Also all things being equal and using the same cartridge a straight arm will perform better mechanically(more rigid and less slop) and electrically(less connections)

 

[marcmorin]

Of course it will pitch at an angle when you lift it up the arm but someone said straight arm roll less than s-arm is not true. they both roll the same amount.

exactly. same offset, same amount of camber :thmbsp:

 

[vinylrayk]

Azimuth shift and vertical bearing orientation

The azimuth shift when riding warps depends on the orientation of the vertical pivot relative to the axis perpendicular to the cartridge body and the offset angle, and has no relation to whether the arm is straight, ‘S’ shape, or ‘J’ shape.

I took a spare 3009/S2 Improved (SN 197057) that I have and made some measurements in order to run a few calculations. To model this, one of the measurements I had to make is the angle by which the vertical pivot (the knife edge) deviates from the "effective length" line that runs through the stylus point and the pivot. Because the 3009 is a "J" shape arm, this angle must be measured separately, since it is not the same as the offset angle.

I'll call this angle T (tau), and on this 3009 it appears to be 'exactly' 15deg. The total angle between the cartridge axis and the perpendicular of the knife edge axis, which I will call B (beta), is

B = T + Offset Angle = 15deg + 22.6deg = 37.6deg.

The common base for tying everything together is the geometric plane that the arm is in. This 'tonearm plane' tilts or rotates about the arm's vertical pivot, i.e., the knife edge bearings. The location and orientation of the cartridge in this plane determines whether and by how much the cartridge azimuth will rotate, or shift, because of the knife edge angle when the cartridge rides up and over a warp.

For the analysis, let's consider a hypothetical 1/4 inch (6.35mm) warp. We first have to project the effective length of the arm to the effective length acting to rotate the tonearm plane about the knife edge axis.

Projected arm length = (231.2mm) x (Cos 15deg) = 223.32mm

The 1/4 inch (6.35mm) warp acts on this projected arm length to rotate, or tilt, the tonearm plane.

Tonearm plane tilt = Arcsin(6.35mm/223.32mm) = 1.63deg

Sounds reasonable. Now we need to translate that into azimuth shift experienced by the cartridge. The amount of this 1.63deg tonearm plane rotation that gets translated into cartridge azimuth shift is proportional to the Sine of the angle B:

Azimuth shift = (1.63deg) x (Sin B)
= (1.63deg) x (Sin 37.6deg)
= 0.99deg

So, in this 3009, the cartridge riding up and over a 1/4 inch warp also rotates counterclockwise for an azimuth change or shift of 0.99deg. Let's do a quick reality check on the math model. In arms where the vertical pivot bearing axis is perpendicular to the cartridge axis, the angle B is zero, and so the azimuth shift on a warp is (1.63deg) x (0) = zero. A classic and clear visual example of this is a Dual 1019.

So, how audible would a 0.99deg shift in azimuth be? Well, that's one of those questions where, if you ask 3 people, you get 4 answers. I would think at this point that that the direct audible effects of the warp (flutter effects due to stylus scrubbing or skipping due to the cartridge body bottoming out) would be of more concern than the azimuth shift.

For comparison, I looked at a SME M2. I don't have one of these but the dimensions are in the VE database. The M2 is a straight tube design with an offset angle at the 'headshell'. This is easier to analyze because, in this case, the angle T is zero and the angle B is simply equal to the offset angle. For a 1/4 inch warp:

Effective Length = 233.62mm
Offset Angle = 23.62deg

Tonearm Plane Tilt = Arcsin(6.35mm/233.62mm)
= 1.56deg

Azimuth Shift = (Plane Tilt) x (Sin B)
= (1.56deg) x (Sin 23.62deg)
= 0.62deg, which is about 1/3 lower than the 3009.

Consider this:

The warp that's causing the azimuth shift in the cartridge is also causing an azimuth tilt in the record surface itself:

Let's say there's a 1/4 inch warp at the outer edge of the record. The record label is still sitting flat on the platter. (If the label is warped too, then the record is most certainly toast.) For a 1/4 inch rise over the distance of the recorded area (5.75 - 2.375 = 3.375 inches), the record surface itself has a tilt of:

Arcsin(0.25 inch/3.375 inches) = 4.25deg

Sooo, the azimuth tilt in the warped record surface itself is far greater than the azimuth shift caused by a 3009 or M2 vertical knife edge being "sub-optimally" oriented. Because the azimuth shift is in the same direction as the azimuth tilt in the record surface, the relative azimuth shift between the cartridge and the record surface deceases, rather than getting worse, i.e., the combined effects subtract instead of adding together.

Now, get ready to throw rocks at me:

The calculated data contradicts the widely held belief that the azimuth shift due to vertical bearing mis-orientation is a design fault. In practice, the effect of the azimuth shift is a good thing, as it helps compensate for some of the azimuth tilt introduced by the warp in the record surface itself. This would also hold true for other arms that have a vertical pivot orientation similar to the 3009/M2.

 

[marcmorin]

The calculated data contradicts the widely held belief that the azimuth shift due to vertical bearing mis-orientation is a design fault. In practice, the effect of the azimuth shift is a good thing, as it helps compensate for some of the azimuth tilt introduced by the warp in the record surface itself. This would also hold true for other arms that have a vertical pivot orientation similar to the 3009/M2.

now to really throw a wrench into this.........you forgot to include another offset. :thmbsp:

good stuff by the way

 

[getter365]

(dirty word alert) How about all the automatic turntables - Dual, Miracord, Garrard, BSR BIC. And a lot of tables besides Thorens. Lenco. B&O. Connoisseur.
S-shape arms in the 70's were predominately of Japanese manufacture.

True sregor and ehoove. Point well taken. I should have known to think first, then post. This thread is warping my mind a bit.

 

[lini]

It's correct that a vertical pivot axis arrangement perpedicular to the offset angle (of headshell, cart and cantilever) should prevent sideways roll with height change. The amount of roll when deviating from the manufacturer geometry to a slightly different one (e.g. one of the usual three, be these calclated for RIAA or DIN lp playback area...) will be pretty insignificant, though.

And alignment jigs and abbreviations certainly are just as possible on straight arms. Only differences there are that the cart in that case should be centered on the longitudinal axis of the offset part of the headshell, and the jigs or abbreviation distances will rather reference to the front of that headshell - and hence will also require the use of more proprietary headshell designs... Examples for such jigs would be those from Dual or also the one that came with the original long-slot headshell kit for the Philips AFx77 tables.

Greetings from Munich!

Manfred / lini

 

[WaynerN]

It's correct that a vertical pivot axis arrangement perpedicular to the offset angle (of headshell, cart and cantilever) should prevent sideways roll with height change. The amount of roll when deviating from the manufacturer geometry to a slightly different one (e.g. one of the usual three, be these calclated for RIAA or DIN lp playback area...) will be pretty insignificant, though.

And alignment jigs and abbreviations certainly are just as possible on straight arms. Only differences there are that the cart in that case should be centered on the longitudinal axis of the offset part of the headshell, and the jigs or abbreviation distances will rather reference to the front of that headshell - and hence will also require the use of more proprietary headshell designs... Examples for such jigs would be those from Dual or also the one that came with the original long-slot headshell kit for the Philips AFx77 tables.

Greetings from Munich!

Manfred / lini

Thank you Manfred!

'ner

 

[lini]

I think it easiest to imagine with a finite plane in mind - like for example the flat lid of a chest. Here it's obvious that everything on that lid that's oriented perpendicular to the axis of the hinges won't show any sideways rolling, when the lid is lifted or closed. The actual shape of the tonearm tube now kinda drowns in that plane - i.e. any arbitrary shape that connects the oriented thingy to the hinge axis would do the job, and one could simply imagine that shape hidden in the lid and not cut out yet.... But of course some ways of connection would be more advantageous regarding lateral balance than others.

Greetings from Munich!

Manfred / lini

 

[Rowdy011]

I heard through an audiophile turntable site "that a straight arm and a belt drive is the best for turntable set up". If your talking about turntables that cost less than $2000.00 it really doesn't matter. I personally have 2 turntables, Pioneer PL-518 and a Garrard Zero 100. The Garrard Zero 100 has a zero tracking tone arm that is pivoted head that stays tangent to the records groove from start to finish, zero tracking error

 

[grottyash]

Bump?? Surely the thread has run its course!

 

[bluesky]

This is an outrageous thread. Should be a sticky.