Unipivot wobble

[cobbers]

Didn't the KML have a problem with the Mercury corroding the 'baths' over a period of time (I seem to remember something about a change of material during the production)?

 

[sonddek]

Gently tap a table sideways and a unipivot will behave exactly as Steve describes.

Gently tap a sideways uni-pivot sideways and it will behave exactly like a table.

 

[RJohan]

KML, the perfect tone arm for mad hatters!

 

[Vinny]

Didn't the KML have a problem with the Mercury corroding the 'baths' over a period of time

Mercury will dissolve most metals - that is what amalgam is, as used for traditional tooth fillings - silver amalgam. Add in the effect of the current being carried.... OK in plastic, wood, leather etc.

 

[Tony L]

IIRC the KML had a reputation for the pins corroding, so even if you can source mercury (and would want to) it likely won’t work too well now.

 

[Sue Pertwee-Tyr]

The more I think about this the more I suspect it is structural (floor/table) related. It is the only thing I can think of that would clearly impact a mass below the pivot point in the way described.

It could just as easily be footfall, passing trucks etc. A suspended wood floor is essentially a diaphragm/soundboard. It moves. A turntable stand, especially if mass-loaded (e.g. big heavy amps etc) can amplify the movement or lower it in frequency. This is exactly the sort of thing a unipivot will react to as it’s mass is suspended. Gently tap a table sideways and a unipivot will behave exactly as Steve describes.

Thanks to everybody for the input. I think I’ve got to grips with it. Two things:

1) I think there might have been an extra twist in the arm leadout which imparted a tad too much anti skate bias; and
2) I think the sofa I sit on was in contact with the TT motor mains lead which is dressed down the side of the table, so if I shifted my ageing carcass, this could get conveyed to the table via the (slightly springy) mains lead.

Moving the sofa slightly further away, and letting the leadout wires uncoil before reconnecting the arm, seems to have sorted it. I can replicate the motion, but only by physically disturbing the table as Tony says, and it damps itself within a few oscillations.

 

[Craig B]

Ah yes, the oft overlooked critical arse alignment.