A novel take on a Uni-pivot arm

[Marra]

A couple of pics of my build so far. I used Ed method of adjustment looping the thread round a 1.5mm pin and tying a knot to give single point?
There is as yet no anti skate added but I am having difficulty getting the arm to be stable and balance out.

[Brumm]

As I've mentioned, the Blackbird pivot point is tungsten. From the beginning I decided that absolute hardness was not as important as ease of removal and sharpening. I reckon you can remove, sharpen, and re-insert the Blackbird's pivot in less than five minutes.

Maybe it would be important to know if you distinguish between tungsten (the metal) and tungsten carbide (a chemical compound).
Tungsten is not really a very hard metal, but the carbide is! Although your remark that your pivot is easy to sharpen indicates that you really mean the metal. Do you use a TIG electrode?

Other contributors here seem to mean the carbide (as in engravers). That would be much more difficult to sharpen.

Greetings,
Hansrudolf

[mred]

A couple of pics of my build so far. I used Ed method of adjustment looping the thread round a 1.5mm pin and tying a knot to give single point?
There is as yet no anti skate added but I am having difficulty getting the arm to be stable and balance out.

Good work, it looks great.
What are the tube like things that the  strings are running through to your adjusters?

[Chrisg139]

Hi All
Correction- I should have stated my pivot is tungsten carbide!
Chris

[SUPATRAC]

Maybe it would be important to know if you distinguish between tungsten (the metal) and tungsten carbide (a chemical compound).
Tungsten is not really a very hard metal, but the carbide is! Although your remark that your pivot is easy to sharpen indicates that you really mean the metal. Do you use a TIG electrode?

Other contributors here seem to mean the carbide (as in engravers). That would be much more difficult to sharpen.

Greetings,
Hansrudolf

Yes, I use tungsten, not carbide. It is considerably harder than most steel, so I wouldn't call it soft. I understood that carbide is not that much harder, but thanks to your comment I now see that the difference is significant. Unlike a diamond stylus, for example, the pivot point is not dragged any great distance in normal use - the contact is actually very static - so I would not expect it to degenerate at the rate of a stylus, which has a much more arduous job. At some point I may do more research into the ideal pivot, but the good news is that an upgrade will be as simple as removing an M4 bolt and replacing it with another.

[Marra]

Good work, it looks great.
What are the tube like things that the  strings are running through to your adjusters?

Hi Ed; thanks for the compliment. The plastic things are shoulder washers as used when mounting heatsinks to TO220 transistors

[vitesse]

Amazing work Peter! I'm interested in your diamond pivot. How did you source or make that?

Yes, diamond grinding wheel dresser I cut a thread into: but be aware many sold on aliexpress have inferior or off-centred rough ends which will make alignment more difficult.

This really is a stunning sounding arm now: there's no need for a longer arm and introduce more resonance and inertia problems, I'm hearing no distortion with this short arm set up accurately.

happy listening, Peter

[vitesse]

but I am having difficulty getting the arm to be stable and balance out.

It's important to have the pivot bolt or hanger adjustable: you'll find a thread position slightly forward of vertical most stable.
Disconcerting that the arm may seem unstable & not balance easily between dive and arc up, but don't worry - once set correctly with cartridge VTF the arm is rock solid tracking the groove. This design really is a Super Tracker

Peter

[Tobbe]

So, where do one find good tungsten points at reasonable cost? Are there any threaded variants that can make adjustments easy?

[SUPATRAC]

So, where do one find good tungsten points at reasonable cost? Are there any threaded variants that can make adjustments easy?

Just use a stainless steel bolt, sharpened to as fine a point as you can manage. A household drill can be used to achieve this. I don't believe that a diamond or tungsten pivot bolt will sound significantly better, even if they do stay sharp for a while longer. Honestly, a hand sharpened steel bolt will deliver astounding results.

[Tobbe]

Just use a stainless steel bolt, sharpened to as fine a point as you can manage. A household drill can be used to achieve this. I don't believe that a diamond or tungsten pivot bolt will sound significantly better, even if they do stay sharp for a while longer. Honestly, a hand sharpened steel bolt will deliver astounding results.

Ah, that sounds great! Makes it a bit easier to find parts

[vitesse]

So, where do one find good tungsten points at reasonable cost? Are there any threaded variants that can make adjustments easy?

I found that stainless didn't sharpen to a good point so well. As previous posts suggest, look for tungsten engraving point or centre punch, here's a cheap one:
https://www.aliexpress.com/item/32918757797.html

[SUPATRAC]

I found that stainless didn't sharpen to a good point so well. As previous posts suggest, look for tungsten engraving point or centre punch, here's a cheap one:
https://www.aliexpress.com/item/32918757797.html

Run a grinding disc and hold the bolt so that the grinder is moving towards the point. Roll the bolt with an Allen key. With practice you can get a pretty sharp point, limited mainly by the fineness of the grit disc. I reckon you can get quite an optimal pivot bolt that way with steel or stainless. But even careful use of a fine file alone will gain you tonearm paradise.

[wenig watt]

Ok,
I'll just use a thick old gramophone needle. Glued in with epoxy resin glue...
The experience with the Decca ffss is, as suspected, spectacularly good. All the dynamics and resolution without tracking problems.
It would certainly be a sensible collaboration to set up a Decca Blackbird. With diamond bearing and virgin hair suspension. 18.000,-? Just not to be perceived as unserious?
I have never heard a record with such incredible dynamics and clarity.

Best regards

Arndt

[wenig watt]

It sounds like the scanning diamond is tied directly to the bearing. Nothing disappears in resonance. Not the dynamics and not the details. Wow, Vlad's phono is not in the way either.

best regards

Arndt