Fidelity Research FR-64x


 Fidelity Research FR-64x.....(with silver wire ).  Is this arm still considered  viable today ?

offnon57

@sampsa55 , Thanks for enriching my tonearm collection with

FR-64 fx. I own both 64 S kinds in the sense of silver and copper

wire. I also own Ikeda 345 . Alas not FR64 fx. But I need to start with

 my Sumiko 800 (''the arm''). The arm is designed by physicist David

Fletcher and (hand) made by his master machinist Demian Davidson

from 160 parts. The curious things are: The arm looks like a Breuer

twin but while Breuer refused to make any additional counterweight

for his customers Fletcher designed 6 different counterweights for

his Sumiko. The reason being to provide the right weight for the

carts from 6- till 25 g. This way each individual cart could be adjusted

such that the counterweight would be as near as possible to the

pivot. This seems to be relevant for both: arm mass as well for

the inertia. Lew is very fond about Newton while ''mechanics'' is the

 best established  physical science. As lawyer I need to pretend

to know everything otherwise nobody would be willing to hire me.

In this forum and ''among friends'' I don't need to pretend. So I

hope ''our Lew'' will explain ''the mechanics''. This would be more

in accordance with his eloquence then his modest contribution

about silver oxide versus copper kind (grin).

@nandric Sorry! I meant @chakster. He acquired an FR64fx to use with his FR7 & SPU.

And regarding the mechanics, since you are adjusting both the distance and the mass so that they balance exactly the same thing on the other side, it's not obvious to me why anything important would really be different. If you're moving the same mass to be closer, then you are clearly having an effect, but then you would also need to adjust the mass on the cartridge side to remain in balance. But I'd be happy to be educated on this.


@sampsa55 
For a point mass the moment of inertia I = mass x Radius ( distance from pivot ) squared. The further you push a weight out the moment of inertia increases disproportionately ( by the distance squared ).

@dover 
Since the torque created by the mass of the cartridge that you're trying to balance is force x distance, a larger counterweight closer to the pivot can have the same torque but lower moment of inertia. Ok. Thanks.