making a tonearm...

[maxro]

Originally posted by EC8010
Oh my! I've just seen that headshell with adjustable azimuth. If there's one place where we don't want extra mass and a loss of rigidity, it's the headshell.

Do you mean the 47 Labs headshell? It doesn't adjust azimuth, it auto-corrects for tracking angle across the plane of the record. And is also supposed to isolate the arm from affecting cartridge resonances. I don't know about that second point. I think it would just make calculating the resonant frequency more compicated as we have two pendula to deal with. I agree, it seems like a crazy idea, but that's not going to stop me from trying it.

Taking maxro's points:

1. True, but it can be reduced.
2. Many arms are like this. But they don't have to be. My arm has its pivot at record height and has the counterweight only sufficiently low that the centre of gravity is fractionally loweer than the pivot.
3. True, but this is minimised if the stylus is on the centre axis of the arm.

Have a look at my arm and see what you think.

Unipivot pick-up arm

On point 3: The stylus being on centre will prevent sagging of the arm when you drop the needle onto the record, but azimuth will still change as the arm moves over bumps. It is a function of the cartridge being at an angle to the line from pivot to stylus. The way to avoid this, without placing limitations (magnetic or otherwise) on the unipivot, is to make the arm so long that an offset headshell isn't necessary. Or, use the pivoting headshell and a short arm can be used with no offset.

I had a look at your arm. Nice work. I like your logic, too. Why buy an expensive tonearm when you can spend that money on fun tools to make your own?

I may make two arms, one with pivoting headshell and one without.

Max

[EC8010]

Do post some pictures when you make your arms.

[tmblack]

How do you shield the wires to the cartridge?
I get lots of hum in a wooden tube tonearm.

Tom

[Nanook]

shielding the tonearm cables can be as simple as wrapping them in metalized mylar , or tin foil and attaching a wire from the shield to ground. Also where is your motor in relation to the tonearm?

[tmblack]

The motor is on the opposite side of the arm. Do you wrap the shield inside the tonearm?

Where do you obtain the metallized mylar?

Tom

[Nanook]

metalized mylar is sometimes sold as "emergency blankets" , you know those ultra thin, I can't possibly stay warm with THAT...

http://www.hisystems.co.uk/emergblk.htm

cheap and enough mylar to last a lifetime!. I'd just tape a tinned end of a wire to the mylar. Should work. Alternately you can use thicker tin foil or light weight copper foil if you can find some. Not sure if anyone sells a DIY type wire shielding material ...

[Jezz-the-Fezz]

Yet another way that I've used before is to salvage some of the braid from a section of co-ax. when you pull it correctly, it reduces in girth, AND you can solder it without difficulty. You can also pull threads out to reduce mass if required.

I've been toying with a uni-pivot design that I'd like some comments on. The problem I percieve with many unipivots is a tendancy for dynamics to be compressed. This usually is because all of the motion as well as the securement of the arm rests about one bearing, which often is given to a degree of play. Without getting embroiled into any spurious debates, I'd cite the Naim Arrow as having this virtue inbuilt in its very concept. Where there is a feasability for transient energy from the disk to pull the arm along with it (and don't forget the the compensatatory rearward motion) this is definately going to happen. Although I can understand the numerous intrinsic virtues of magnetically stabilised bearings, I cannot for one moment imagine that a magnet will absolutely resist a transient pull or "drag" which for my mind, puts it in the same arena. Also, by decoupling the arm from any kind of securing, you're also depriving it of any means of rapidly dissipating any standing energy. Hmm.

I remember reading a review some years ago of a Well Tempered design that incorporated a silver high mass tone arm apparently supported only by "fishing line!". The vague description simply got my brain fuzzing over the different ways in which this could be accomplished. After battering all of the first ideas that sprang to mind, I came up with what I hope is a fairly origional idea that owes more to the torsional properties of fishing line than any thing else.

The "bearing" consists of a horizontal coupling between the tonearm and the mounting, being the smallest measure of line required to execute the arc (dependant on the tonearm length of course) of an LP. Where the couplings are coneshaped, the degree of line required should be short enough to bear the weight of the arm without showing any secondary flexing. In order to provide a mechanical link with the base to dissipate residual energy, some measure of the arm (preferably towards the "bearing") should be immersed in a heavy silicone solution.

Other than that, all of the usual gravitational control methods apply. Any thoughts?

Cheers, Jezz

[maxro]

Jezz,

Can you draw us a diagram of your cone and thread idea? I can't quite picture it from your description.

Oh, and that should be Naim ARO.

Max

[Jezz-the-Fezz]

Sorry - absolutely right; Aro - but at least that means you're familiar with the "cup & saucer" principle. In answer to your request, I've knocked up the following diagram of the "bearing" or union as I supose would be more accurate (only a schematic).

Cheers, Jezz

[Nanook]

basically the tonearm is supported on the "paddle" which, inturn is supported in a silicon viscous fluid and by a thread.