Item Audio "Spoke" for the Linn LP12 anybody..?

[sq225917]

OK, you said the spokes would not stretch or compress, and I was pointing out that all load on them is torque in one direction or another- and they are equally strong/weak in all directions to torque/bending. A point you seem unable to understand. They are only potentially ever in tension when the deck is starting up, once at speed, no way no how.

The reference to the lack of a centre point is in response to your comment about them being arranged tangentially to platter rotation and equidistant and equiangular to each other and the bearing centre, and making rotation of the sub-chassis relative to the motor in the vertical axis all but impossible. My point being that they have an exactly equal effect on both the vertical and horizontal compliance of the subchassis.

Their locations around the bearing means nothing to anything as the bearing is not the centre of the sub-chassis mass once it is in motion stimulated by footfall or the motor- the motion centre point is actually a small arc between the bearing and the motor and probably sits on the edge of a circle linking the three spokes.

This mod will equally affect both vertical and horizontal compliance of the suspension equally because the subchassis does not rotate around the centre of the three spokes (the main bearing) and that is the point I was making. That it will introduce as many problems as it ameliorates.

 

[sonddek]

A point you seem unable to understand.

...

 

[sonddek]

Now for the errors:

They are only potentially ever in tension when the deck is starting up, once at speed, no way no how.

The motor continuously applies torque to the subchassis/platter/arm system, otherwise you could disconnect it once the record was up and playing. The rods will therefore constantly be in tension. All the time. That's what they're for. Let me know if you need me to explain why I think that, with my usual lack of understanding.

The reference to the lack of a centre point is in response to your comment about them being arranged tangentially to platter rotation and equidistant and equiangular to each other and the bearing centre, and making rotation of the sub-chassis relative to the motor in the vertical axis all but impossible.

The torque has an axis. All torques do. It just isn't coaxial with the bearing. That doesn't affect the fact that the three rods in a horizontal plane are able to oppose a torque whose axis is vertical.

My point being that they have an exactly equal effect on both the vertical and horizontal compliance of the subchassis.

No they don't. There are three of them, at a distance from each other, on a horizontal plane. That gives them the ability to oppose twists and pulls in the horizontal plane. In the vertical axis they have very little ability to resist. If you wanted them to resist motion in a vertical plane, you would need to put the three of them in that plane. But they're not in a vertical plane, they're in a horizontal plane, which gives them the ability to resist vertical-axis torques.

This mod will equally affect both vertical and horizontal compliance of the suspension equally because the subchassis does not rotate around the centre of the three spokes (the main bearing) and that is the point I was making. That it will introduce as many problems as it ameliorates.

This analysis seems wrong. None of the rods will resist vertical motion very well since they can bend. But horizontal deflections and twists will be resisted by one or more of the rods because it will require stretching or compression of the rod(s).

 

[Nik]

If this is a good idea (I don't think it is), then why do it in such a clumsy, ugly way? Why drill holes through the top plate when you can do it all underneath without any holes?

Also, it looks to me as if the rods are not given freedom of vertical movement (articulation) at each end by using bearings or bushes (like a Panhard rod), but are clamped, so they are expected to bend instead. They will be flexible in the vertical direction (or any other at right angles to their length) but will act like leaf springs and alter the compliance of the suspension system.

 

[sonddek]

Also, it looks to me as if the rods are not given freedom of vertical movement (articulation) at each end by using bearings or bushes (like a Panhard rod), but are clamped, so they are expected to bend instead. They will be flexible in the vertical direction (or any other at right angles to their length) but will act like leaf springs and alter the compliance of the suspension system.

While that's true, the amplitude of suspension oscillations is supposed to remain very small indeed. In the limiting case of no vertical amplitude the fact that the rod is comparitively amenable to shear deflections means that the rigid fixing of the rod ends shouldn't matter much. I'm sure it does affect the suspension, and bouncing the platter will probably show that, but the effect is least at zero vertical displacement, where, ideally, the record is played. Nobody bounces her platter while listening to a record. I hope.

 

[zener]

you cant do it underneath , the springs are in the way..unless you know how to pass a rod through a spring

 

[James]

It's not 'magic', but the LP12 springs do have to be rotated to achieve correct alignment and bounce; there are two reasons for this 1/ the two ends of the springs are not entirely parallel (despite being ground flat) and, 2/ the centres of the spring ends vary in terms of vertical axis alignment.

The bounce is not 'magic', I know. The magic to which I was referring is the LP12 effect on music, when the set-up is spot on.

James

 

[Nik]

you cant do it underneath , the springs are in the way..unless you know how to pass a rod through a spring

We can put the rods wherever we can link the sprung and unsprung masses with the right geometry. The springs only get in the way if you want them to.

But I'd like to use the existing spring mounting points so all we need are some brackets/outriggers (imagine washers with a lug attached) to bring the rod mounts just outside the springs.

 

[dave]

Thoughts on the rods producing noise (and ending up as part of the signal) as they flex a bit during platter rotation?

 

[zener]

Drill some more holes in the top plate and fit some long bolts and secure them, underneath, via the spoke to the subchassis. I suspect the set up requires access to the spokes for fine adjustment of length, which maybe was thought too tricky with the sub chassis in the way and various bits of wood and the odd cable etc etc.

 

[i_should_coco]

The Pink Triangle solution.

 

[pure sound]

Can someone explain how restricting the isolation in the horizontal plane when much of the recorded information is cut in that plane can actually help matters?

 

[zener]

If you are very pitch sensitive , any movement in the horizontal plane will effect the pitch of the signal from the TT and you wont like the resultant sound ..ie the relationship between the motor and the platter , ie the platter is able to move toward and away from the motor while the motor stays still.

 

[pure sound]

Most people are also sensitive (almost without realising it) to increases in low level grunge and its effect on dynamic range & the purity of notes. I get the pitch stability 'advantage' but I'd be concerned about other aspects becoming compromised.

 

[zener]

you asked a question and I answered it , if you have perfect pitch any "wow" will really piss you off. Grunge and the like, becomes irrelevant. We are all different in our perception of what is exceptable , the LP12 appeals to those who like their music sounding fun , but flawed none the less

 

[afewbeers]

Interesting tweak, and one I have considered before. Unfortunately, there are several issues that have largely now been covered; the coupling of the sub chassis to the plinth, and secondly the fact that it assumes a centre of rotation around the main bearing, which is not the centre of rotation for drag induced instability.

This is one of the reasons why a LP12 with correctly set up suspension does actually sound better, in my opinion, as there should be no tendency for the deck to bounce with any rotation component.

Most people recognise that the LP12 is flawed, pretty much like every other turntable to a greater or lesser extent, but it is capable of high performance. Some of Linn's upgrades are expensive but most who have heard them (particularly the Radikal) will accept that they have raised the bar. This would clearly indicate that there is continuing scope for improvement. I'd like to keep an open mind on this mod, but from what I can see it would seem fundamentally flawed.

 

[pure sound]

I didn't ask how it'd improve the speed stability but how restricting the isolation in the horizontal plane would help.

Bolting up the subchassis would also improve the speed stability but it'd sound pretty awful.

 

[Nik]

The Pink Triangle solution.

What? The solution is to use a budget Linn arm??

 

[Nik]

While that's true, the amplitude of suspension oscillations is supposed to remain very small indeed. In the limiting case of no vertical amplitude the fact that the rod is comparitively amenable to shear deflections means that the rigid fixing of the rod ends shouldn't matter much. I'm sure it does affect the suspension, and bouncing the platter will probably show that, but the effect is least at zero vertical displacement, where, ideally, the record is played. Nobody bounces her platter while listening to a record. I hope.

Just think about why there's a suspended subchassis in the first place, not just on an LP12 but on an AR XA, TD150, and all the rest.

 

[sonddek]

Just think about why there's a suspended subchassis in the first place, not just on an LP12 but on an AR XA, TD150, and all the rest.

I understand very well why the subchassis is suspended. The problem is that the suspension introduces an additional resonant energy store between the motor and the thing it is supposed to accelerate, thereby leaving the platter at the mercy of fluctuating drag and resonant acceleration.

Zener has put his finger on it: do you want inky blacks or instruments which stay in tune. The more elastic stuff you put between the motor and the platter, the more you get the former, not the latter.

That's what this spoke design is designed to trade off. I would be interested to hear its pitch accuracy, regardless of whether it sounds good in other respects or not.