Sideways Uni-Pivot Arm, SUPATRAC Blackbird, formerly "Ekos Killer (Price?)"

[Mr Pig]

Hi booja30, if form and function are not necessarily interdependent try to use squared ball bearings.

You're building a really dumb argument here. When you initially mentioned form in regard to this tonearm it had to be assumed that you were talking about its aesthetic. You could not be referring to its structure as clearly, its structure follows its function fairly precisely. There obviously isn't much effort going into aesthetics at this point, it's a functioning prototype.

But now you bring up a ball bearing, which has a aesthetic dictated by its function, and suggest that's the right way to do it. When that is exactly what the OP has done!

 

[Luca]

Consider architecture. If form was strictly derived from function then many of the world's most iconic structures would be unrecognizable. Of course, some were very forms very much driven by function. But for many others, function was less important. Is it wrong to prioritize factors other than function in every case?

To keep it short, it depends on the type of function to which an architecture must perform. For example, an hospital does not allow for functional digressions.

 

[Mr Pig]

To keep it short, it depends on the type of function to which an architecture must perform. For example, an hospital does not allow for functional digressions.

What are you talking about?

 

[Luca]

You're building a really dumb argument here. When you initially mentioned form in regard to this tonearm it had to be assumed that you were talking about its aesthetic. You could not be referring to its structure as clearly, its structure follows its function fairly precisely. There obviously isn't much effort going into aesthetics at this point, it's a functioning prototype.

But now you bring up a ball bearing, which has a aesthetic dictated by its function, and suggest that's the right way to do it. When that is exactly what the OP has done!

You have lost a part of my post #71: "I'm not referring to this thread but to arms put on the market and followed by someone as a reference object".

 

[Luca]

What are you talking about?

With you about Ekos killer price?
Going from a survey to the project of a prototype this thread seems to me to give space to any rambling consideration.
About the prototype I encourage to do an attempt. I'm sure, it isn't impossible to design a better arm than the Ekos by pieces of extruded alloy.

Bye Bye,
Luca

 

[sonddek]

I want to be able to use tungsten in the counterweight because of its very high density (good for lowering effective mass), and because the counterweight needs to be very low for stability, due to the low pivot point. Space is cramped behind the pivot, so density is required. However, tungsten will affect price, and some may prefer a cheaper counterweight, or to insert damping between weight and box. I don't want to be machining tungsten. Hence the counterweight system will probably be something like the below, where any counterweight of your choice is easily slung under the box. A threaded bolt will wind the counterweight carriage yoke fore and aft. The visible bolts which clamp the counterweight will be thumbscrews or allen socket.

To adjust counterweight one will loosen the two yoke bolts, then wind the bolt at the back, and retighten yoke bolts. I know this is not as convenient as a simple dial as on Ekos, but it provides a certain flexibility for heavy-tracking cartridges and damping options.

This picture shows a weight made from 2x1cm steel bar, but a tungsten rod should be only 6mm dia. and so will allow more fore/aft movement.

 

[sonddek]

To clarify the above, if you are a fan of low tracking weight cartridges like Shure, and you never use higher tracking weight cartridges, you might want to get down to one gram by inserting a heavier counterweight nice and close to the pivot thus lowering the effective mass as seen by your compliant cartridge suspension (easier to waggle). On the other hand you might want to use a greater range of cartridges, or only heavier tracking cartridges. You may have more or less space to play with due to the height of your platter above the arm mount. You may want to spend extra for tungsten, or be on a budget and use brass or steel. You may be a DJ with a 3 gram tracking weight. You may want to damp the counterweight by inserting some rubber between the weight and the clamp system. You can do all this easily with such a system - no machining required, a hacksaw will suffice.

There is nothing wrong with experimenting - it's part of the fun.

 

[James]

I can't tell where the pivot point is. If this is a uni-pivot, how do you adjust azimuth?

 

[Chops54]

I can't tell where the pivot point is. If this is a uni-pivot, how do you adjust azimuth?

See those surface scratches on the front face of the counterweight carrier under the two arm tubes? I imagine the pivot point is low down on there. The arm must hang on tie wires or something from the top of the pivot post, the pivot point sticking out of the post lower down. Gravity will swing that flat face onto the pivot. That blurred image in the foreground might be the pivot post? I'm only surmising of course but that's how I see it. If that's how it works it's quite unique and pretty clever! I could be totally wrong off course

 

[paulski]

See the picture here.

 

[Mr Pig]

There is nothing wrong with experimenting - it's part of the fun.

It's very interesting and congrats for doing it. You never know what will come of it.

 

[sonddek]

See those surface scratches on the front face of the counterweight carrier under the two arm tubes? I imagine the pivot point is low down on there. The arm must hang on tie wires or something from the top of the pivot post, the pivot point sticking out of the post lower down. Gravity will swing that flat face onto the pivot. That blurred image in the foreground might be the pivot post? I'm only surmising of course but that's how I see it. If that's how it works it's quite unique and pretty clever! I could be totally wrong off course

Entirely correct.

Here's a video of one of the first prototypes which makes clear how the bearing works:
http://www.supasound.com/yaw.pitch.mp4

Note that the repetitive oscillations in stylus drag from the signal is directly opposed by the pivot point, so it does not need to be a precision device. The primary oscillating forces are opposed by a steel point against a steel plate, gapless, and not rubbing.It's really difficult to push a nail through a steel plate.

The support ligatures mean that the arm does not suffer from azimuth instability in the way that traditional unipivots do. Here's a video which illustrates pitch/yaw frictionlessness and azimuth stability:
http://www.supasound.com/tapping.mov

 

[paulski]

Any progress?

 

[sonddek]

Any progress?

Yes - as follows:

- prototype 0.1.4 nearing completion
- carbon-fibre arm tube complete except for foam fill and finish
- reinforcement for cartridge bolt site complete
- Linn cartridge compatible third hole complete
- 104 thrust-cages cut, ready for drilling and finishing, though some outside spec
- Linn compatible arm column & pillar design finished and two versions built
- Tungsten counterbalance rod system complete
- ligature/arm suspension system improved and nearly complete
- CAD drawings of thrust-cage, arm-column/pivot nearly complete
- anti-skate device improved

At this rate I am on schedule to have a product for sale within 6 months as hoped.

I will try to find time to upload some new images over the weekend.

Thanks for your interest!

 

[sonddek]

Here's a little snapshot...

 

[sonddek]

 

[sonddek]

This is the carbon fibre tube, with a third hole for Troika fans, and a glued steel cartridge-mounting platform both above and below the carbon-fibre mounting site.

In the background you can see some of the 104 thrust-cages I have cut for a rainy day.

 

[paulski]

Excellent work. I look forward to seeing the whole thing assembled!

 

[jagdesign]

oh exciting, look forward to seeing it come together

 

[Electron]

A really interesting concept. It reminds me a bit of the Well Tempered tonearm but instead of a golf ball in a cup of silicon this relies on the sideways pointing spike to resist the drag from the stylus groove. I wonder if it shares a similar sound signature. My guess is that the Well Tempered would sound more damped in comparison as the silicon not only resists the stylus drag but would help absorb any energy from the cartridge itself. The spike could possibly make for a more dynamic sound and assume that the arm "tube" in this instance would need to dissipate any energy from the cartridge.