Belt vs. Direct Drive

[Slim-Shaddy]

That's pretty cool. What's the advantage? Just another step towards complete motor isolation?

[confused]

Older tables the idler was under and on the inside edge of the platter.  Supposed to give more torque for faster start up, and stable speeds.  This why the changers used them, a stack of records would still play at the correct speed.  That VPI unit is much heavier duty than the old rim drives.

[Slim-Shaddy]

Confused... I'm a little confused Why didn't they just go DD? Wouldn't that give the best torque and start-up?

[confused]

These predated DD.  Later they figured out how to spin the platter by turning it into the rotor, therefore not requiring a mechanical connection from the platter to the motor, only electromagnetic.  Another development that made dd possible was dc servo control motors.  With an ac motor, you couldnot build 1 slow enough for dd, and required somekind of coupling to match motor speed to platter speed.

The new vpi "upgrade" adds a lot more inertia due to the size of the idler.  Old tables had much smaller wheels.

I am digging pretty deep into the cobwebs of my mind, so do not treat this as gospel.

[confused]

Also, if anyone wishes to chime in to correct or corroborate please feel free.  

Holy Cow, I did not know you could modify these posts.  Now I feel like I should go back and fix all my typos!

...OK, I probably won't

[Slim-Shaddy]

right on... This is brand new to me..... How do those 80's commercials go?? Knowledge is Power!!

[MasterBlaster]

I have no clue, but would think that the rim drive would perform better than DD.
The flywheel disk is intentionally weighted to provide smooth consistent rotation.

With DD, I would imagine that slight voltage fluctuations would be easily noticeable
whereas the same fluctuations would be dampened by the flywheel.

That was my thoughts in regards to the TT weights as well. The weight helps
to make the platter behave like a flywheel which provides more consistent rotation.

What say you?

[confused]

Quite discerning!  Some people used to call the servo control sytems never right.  Adding a feedback loop and speed sensing ckt means that the speed is constantly being adjusted!!  New circuits and components allow DC power supplys to output quite steady DC despite AC input changes and some newer tables are dc but no servo with big heavy platters to maintain consistancy.

In the older highend TT the idler was small and platter heavy, just like belts to keep the speed constant using rotational inertia.  All these tables (belt and rim) got a boost in performance when they started using hysteresis rather than induction motors.  Hysteresis motors maintain speed unless the line frequency changes, which unlike voltage is rock steady.

[desperado915]

My Pioneer PL-41 has a 4-pole hysteresis synchronous motor. Rock solid and steady, never misses a beat. I am in the process of restoring and modifying it as we speak. I will post pics when done.

[Slim-Shaddy]

Design me a TT in which the motor can overcome the centrifugal force of a silver dollar placed at the outer rim or the platter. I'll buy it. The point is there is no such thing as perfection in the TT world. The most balanced TT is not going to overcome a mishapen LP, a table .01 degree off balance or a magnetude 1.3 earthquake. The glory of turntables is their ability to be manipulated, recover, and change again without researching which diode, transistor, resistor, or capacitor is best suited for the task.

[MasterBlaster]

Sorry If I'm getting in the way; I cant help but join in the conversation
I just run the forum for Tom. I have no clue about any of this stuff really.

Maybe I should just STFU and admin the site.  

This is a pic of the last turntable I owned:

[Slim-Shaddy]

Admirable!!! Do you still have it? I want one of those for my son!

[MasterBlaster]

I wish.
If I did, I'd be rocking to the Chipmunks right about now!

[Slim-Shaddy]

LOL

[confused]

So finally someone in the 21 century chimes in.  Thanks Master-Blaster!

You need to forgive us audio dinosaurs and all vinyl lovers!

I mostly agree with King-Edwin, a good TT is a good TT, and they all require some compromise from ideal!

And thanks to desperado915 , I forgot the most important word synchronous (though all hysteresis motors are synchronous, not all synchronous motor are hysteresis).

And finally, though I own at least a mile of vinyl (end to end) and I mostly Listen to CD, I will always own a TT.

And lastly, I guess the teacher in me was sprung loose for a minute.  If you would like more details on motor construction PM to get my phone number and we can discuss it in detail.