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Vintage DD turntables. Are we living dangerously?

I have just acquired a 32 year old JVC/Victor TT-101 DD turntable after having its lesser brother, the TT-81 for the last year.
TT-101
This is one of the great DD designs made at a time when the giant Japanese electronics companies like Technics, Denon, JVC/Victor and Pioneer could pour millions of dollars into 'flagship' models to 'enhance' their lower range models which often sold in the millions.
Because of their complexity however.......if they malfunction.....parts are 'unobtanium'....and they often cannot be repaired.
halcro
lewm
13,769 posts
 
"With an unsuspended mass-loaded turntable of any kind, that centrifugal force is absorbed and thus resisted by the mass of the supporting structure."  I don't want to say "I told you so", but I did tell you so back when that was a point of contention among us. Back when Raul was recommending just sitting the naked chassis on a set of AT pucks that were said to have magic powers.  And let me apologize in advance for being pedantic, but this is not a "centrifugal" force at all.  This is a force that is described in Newton's Third Law of Motion: "for every action, there is an equal and opposite reaction". Thus it is a force vector that has a direction described by an arc opposite to the direction of the arc of turntable rotation.  This is why and how the Kronos works; the lower platter, of mass equal to the working platter, is rotating opposite to the direction of the working platter. and this effectively cancels the forces. Otherwise, the tail wags the dog.

And finally, to be even more annoying, there is no such thing as a "centrifugal" force.  The force described in that commonly used misnomer is actually centripetal; to keep the object from flying off in a straight line, a force directed toward (not away from or "centrifugal") the center of rotation is generated and required.


fleib
1,124 posts
 

**Thus it is a force vector that has a direction described by an arc opposite to the direction of the arc of turntable rotation.**

What force vector is that?  If the platter/motor moves it would be in the direction of rotation.  There is no force vector opposite to direction of rotation.  It's the motor unit coupling to the mass of the pod that resists movement.  The mass of the motor is heavy enough to resist, otherwise Raul wouldn't have been able to listen to the table.

Regards,

dover
2,353 posts
 
lewm
06-29-2016 3:43am
"With an unsuspended mass-loaded turntable of any kind, that centrifugal force is absorbed and thus resisted by the mass of the supporting structure." I don’t want to say "I told you so", but I did tell you so back when that was a point of contention among us. Back when Raul was recommending just sitting the naked chassis on a set of AT pucks that were said to have magic powers. And let me apologize in advance for being pedantic, but this is not a "centrifugal" force at all. This is a force that is described in Newton’s Third Law of Motion: "for every action, there is an equal and opposite reaction". Thus it is a force vector that has a direction described by an arc opposite to the direction of the arc of turntable rotation. This is why and how the Kronos works; the lower platter, of mass equal to the working platter, is rotating opposite to the direction of the working platter. and this effectively cancels the forces. Otherwise, the tail wags the dog.

And finally, to be even more annoying, there is no such thing as a "centrifugal" force. The force described in that commonly used misnomer is actually centripetal; to keep the object from flying off in a straight line, a force directed toward (not away from or "centrifugal") the center of rotation is generated and required.

Lewm,
You are wrong when you say there is no such thing as centrifugal force.

Centripetal force is that at a right angle directed toward the centre of the axis of rotation.

Centrifugal force is the apparent force, equal and opposite to the centripetal force, drawing a rotating body away from the center of rotation, caused by the inertia of the body.

Centrifugal and centripetal are opposite sides of the same coin.
If you look at the platter from the outside you see centripetal force, if you sit on the platter you feel centrifugal force - get it.

Newton’s First Law states that “A body at rest will remain at rest, and a body in motion will remain in motion unless it is acted upon by an external force.” If a massive body is moving through space in a straight line, its inertia will cause it to continue in a straight line unless an outside force causes it to speed up, slow down or change direction. In order for it to follow a circular path without changing speed, a continuous centripetal force must be continuously applied at a right angle to its path.

dover
2,353 posts
 
fleib
06-29-2016 7:24am
**Thus it is a force vector that has a direction described by an arc opposite to the direction of the arc of turntable rotation.**

What force vector is that? If the platter/motor moves it would be in the direction of rotation. There is no force vector opposite to direction of rotation. It’s the motor unit coupling to the mass of the pod that resists movement. The mass of the motor is heavy enough to resist, otherwise Raul wouldn’t have been able to listen to the table.

Fleib,
You don’t seem to understand how a direct drive TT works. Half the motor is coupled to the platter, the other half of the motor is connected to the plinth. If you hold the TT upside down by the platter, then the plinth will spin.
The mass of the relative mass of the plinth to the platter is relevant and the rigidity of the coupling of the half of the motor connected to ground affects speed and articulation.
Clearly Raul is unable to here the effects of a rigid plinth and motor coupling in his system.

halcro's avatar
halcro OP
2,664 posts
 
Hi Fleib,
Interesting point. Assuming the motor is still coupled with three rubber pads, it's not only the mass of the pod which resists motion, it's also the integrity of the coupling and mass of the motor unit insuring that resistance. I wonder if performance would improve if the motor unit was bolted onto the pod.

The TT-101 merely resting on the three rubber pads is relying on the 'friction' of the motor-unit mass to transfer this motion energy into the granite plinth.
I believe it's enough but you're right.....it would be better to mechanically connect it but at this stage, I don't know how? 🤔

Regards


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