DIY Tonearm

[Chops54]

Everything can be improved on - I'm not convinced that an Internet design committee is likely to achieve it though. If the intention is to try to make something genuinely better then prototypes will have to be made and compared to each other etc. the only way to know the impact of the bearing is to make it without the decoupling element.

Your mate TPA has a solid one piece pillar for the Aro that he's willing to lend so all we need is someone with an Aro to try it

On a more serious note I think quite a few of us are realists and don't expect to make something better. Just to make something that works well for a fraction of the cost will be an achievement that most of us will be very happy with.

 

[timH]

After all this is the DIY room which I always though stood for do it yourself. I just don't get all this "balance" and morality. Is it moral to build a geddon clone or a DIY hi cap or any of the myriad of electronics bodges

 

[flatpopely]

After all this is the DIY room which I always though stood for do it yourself. I just don't get all this "balance" and morality. Is it moral to build a geddon clone or a DIY hi cap or any of the myriad of electronics bodges

Actually your correct, sorry.

 

[John Channing]

The description of the Funk Firm F*X and a comparison of its resonant behaviour with other arms is interesting. I would guess the "£2000" arm is the SME V and the "£3500" arm is the Linn Ekos SE. I would guess some of the other plots are Rega, Linn and Pro-Ject.

I wonder, based on the above, whether one of the compound carbon/aluminium alloy arroy shafts might work well. The carbon is hard to twist, and the aluminium/carbon layers will damp bending modes.

 

[paskinn]

The description of the Funk Firm F*X and a comparison of its resonant behaviour with other arms is interesting. I would guess the "£2000" arm is the SME V and the "£3500" arm is the Linn Ekos SE. I would guess some of the other plots are Rega, Linn and Pro-Ject.

I wonder, based on the above, whether one of the compound carbon/aluminium alloy arroy shafts might work well. The carbon is hard to twist, and the aluminium/carbon layers will damp bending modes.

The SME arm tube is a highly complex casting of variable thickness magnesium. It sounds quite different to the same arm tube in aluminium. I know because I have samples of both. Regardless of somwe hat dodgy plots (Arthur is busy pushing his own arm) aluminium can sound rather good, open and lively without being bright.
I am not a DIY guy, no manual dexterity, but the DIY arm seems a really good idea. Why not stop nit picking and just forge ahead. People can resume 'debating' once it is built. Should sound rather good. What is there to lose? Good luck.

 

[audioflyer]

If you could see the sketches I'm now work on,it does look very good.

You will get both options for the bearing pillar solid (two parts) and ball decoupled bearing (three parts) so you can decide.

Arm length will be same as the Rega with a three point fixing with up to 10mm VTA easy adjustment. The VTA adjuster is part of the arm mounting base.

The yoke will be split into the body and top cap (which holds the pivot bearing) this will allow easy of alignment and assembly of the arm sleeve through the yoke.

Tonearm lift/lower anybody?

I've started re-modelling the parts up and will post the assembled arm within a 3D pdf.

Sharif.

 

[Chops54]

A lift/lower would be good for me Sharif. The platform would be a handy place for the plug and socket maybe?

 

[John Channing]

The yoke will be split into the body and top cap (which holds the pivot bearing) this will allow easy of alignment and assembly of the arm sleeve through the yoke.

I think the design can be improved by mounting the bearing pivot in the yoke, rather than the top cap. The reasoning for this, is that you want the shortest route possible to mechanical ground in the fluid damped bearing and ideally therefore, you want the resonating arm tube directly coupled to the bearing point. Doing it that way round also makes it easier to isolate the counterweight which is attach to the top cap. Maybe this is not something you want to do on the first prototype (which is more of an Aro clone), but it is worth thinking about once we get onto the tinkering.

 

[audioflyer]

This is just an overview of what’s to come.

Left hand side of the drawing showing bearing post with VTA adjustable mounting.

Right hand side showing an overview of tone arm with Rega geometry.

The flanges on the side of the yoke are placed low down and should add further stability to any side way forces.

Counter weight stub will be rigidly coupled to the yoke with the counter weight decoupled with two 'O' ring inserted with in.

Sharif.

 

[Paul R]

Obviously not an ARO. Looks good. Do you have a mechanism in mind for lateral balance?

Paul

 

[audioflyer]

Obviously not an ARO. Looks good. Do you have a mechanism in mind for lateral balance?

Paul

I've not work one out yet but open to suggestion?

Sharif.

 

[John Channing]

This is just an overview of what’s to come.

Left hand side of the drawing showing bearing post with VTA adjustable mounting.

Right hand side showing an overview of tone arm with Rega geometry.

The flanges on the side of the yoke are placed low down and should add further stability to any side way forces.

Counter weight stub will be rigidly coupled to the yoke with the counter weight decoupled with two 'O' ring inserted with in.

Sharif.

You have added some side stabilization weight to the bearing cup?

 

[audioflyer]

You have added some side stabilization weight to the bearing cup?

My think is that by having the side stabilization weight at the bottom of the bearing cup should help the arm to remain perpendicular to the bearing.

I'm looking at the tail wagging the dog scenario, where some of the energy from the cantilever will travel along the arm tube to the bearing and set up a small side way movement below the center point of gravity, by having the extra weight low down should offer a counter weight effect to these small movements.
Again just my thought this may lead to better resolution.

Sharif.

 

[Paul R]

I've not work one out yet but open to suggestion?

Sharif.

The easy way would be an eccentric counterweight. But I don't know whether there are practical implications for setup. I think it might need to be something that can be adjusted exactly and then locked, independently of the tracking force adjustment.

I have a Decca International unipivot in the loft, I think it uses the eccentric counterweight, and some sort of magnetic vertical decoupling. I'll dig it out and see how it handles.

Paul

 

[John Channing]

The flanges on the side of the yoke are placed low down and should add further stability to any side way forces.

Can you show another view so I can get a better idea of what those look like? I assume this is a one piece machining added to the cup, not something adjustable? If the cup is machined from aluminium alloy, it is not going to add a great deal of stability compared with the counter weight that already plays that role being mounted well below the pivot point. Just a thought.

 

[audioflyer]

Can you show another view so I can get a better idea of what those look like? I assume this is a one piece machining added to the cup, not something adjustable? If the cup is machined from aluminium alloy, it is not going to add a great deal of stability compared with the counter weight that already plays that role being mounted well below the pivot point. Just a thought.

The cup/yoke views.

Sharif.

 

[mcai7et2]

One problem I can see here is that you have made the machining of this part much more difficult. A simple cup can be cut on a lathe from bar stock, with the holes for the counterweight and armtube cut later. This will need to be machined from a block, and will cost quite a lot more to produce.

I guess your machine shop can help you figure out the impact, perhaps it isn't much more

 

[John Channing]

One problem I can see here is that you have made the machining of this part much more difficult. A simple cup can be cut on a lathe from bar stock, with the holes for the counterweight and armtube cut later. This will need to be machined from a block, and will cost quite a lot more to produce.

I guess your machine shop can help you figure out the impact, perhaps it isn't much more

I would tend to agree. You could also keep rotational symmetry and improve balance by making it bell shaped/flared at the bottom. This could still then be cut on a simple lathe.

 

[audioflyer]

One problem I can see here is that you have made the machining of this part much more difficult. A simple cup can be cut on a lathe from bar stock, with the holes for the counterweight and armtube cut later. This will need to be machined from a block, and will cost quite a lot more to produce.

I guess your machine shop can help you figure out the impact, perhaps it isn't much more

I would tend to agree. You could also keep rotational symmetry and improve balance by making it bell shaped/flared at the bottom. This could still then be cut on a simple lathe.

Right had a chat with one of the graduate mechanical engineers who put me on the straight and narrow, just go to show how much I forgot.

There is no benefit by adding side stabilization to the cup but there maybe a small benefit of belling the cup.

Sharif.

 

[John Channing]

Right had a chat with one of the graduate mechanical engineers who put me on the straight and narrow, just go to show how much I forgot.

There is no benefit by adding side stabilization to the cup but there maybe a small benefit of belling the cup.

Sharif.

Not sure I agree with that, as they are equivalent in my mind. As far as I can tell, all that matters is how far the centre of mass is below the pivot point. Basically, the bearing housing cup and counter weight system is like a pendulum, driven by the stylus moving through the groove on the record. For it to be stable, you want the natural frequency of oscillation to be lower than the lowest frequency note you want to be able to reproduce. For small displacements, the time period of oscillation is

That is, it depends only on length of the pendulum and we are fairly tightly constrained by just how far the centre of mass can be from the pivot point, unless you raise it well above the surface of the record which generally is not done. Might be worth trying though!