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In Reply to: Thorens pic of the day posted by user510 on January 27, 2007 at 00:21:47:
Since the eddy current system is similar to Garrard's, I know just what kind of eureka moment it is when you see the full design intent.But there is something more.
Unlike the 'best-it-will-ever-get' sort of design that a belt-drive uses ... ie the motor and drivetrain will only ever get less efficient with time and the only solution is to replace it or overwhelm it electronically with an expensive freq-regen system.....
The classic Idlers like the 124 and 301 set up a system wherein the motor / drivetrain was actually built to be capable of a much greater rotational force .... and when time and tide slowed things down, 30, 40, even 50 years on --- the adjustment of a dial brings back the needed extra power, held wisely in reserve.
Both Garrard and Thorens were well aware of the mischievous detriment that time can play on a complex mechanism, having both been commercial Phonograph manufacturers for many many years by the time of these two classics....
Genius, I think. Something the Future Obsolescence Dept would certainly not approve of these days.Consider also that unlike beltdrive's 'running-at-full-capability' approach, wherein the only likely change in performance over time is downhill, the Idlers are running somewhere in the middle range of their capabilities, like a seasond runner in mid-race.
Genius, and genius of the oldschool, to whom we have to tip our virtual hats.
J.D.
Follow Ups:
......the idea of using eddy currents as a brake mechanism. While I was googling up explanations of the effect I came across some interesting stuff. It seems that diesel-electric locomotives have been using eddy current technology to brake their wheels for quite some time now. Imagine the forces involved!As I consider it one idea that does to occur to me, and I'm not sure it is correct, is that the eddy brake might offer a means of smoothing/filtering out at least some of the cogging effect off the motor.
While the motor is driving the large pulley in one direction there is a measured amount of force applied to that same pulley in the opposite direction, pulling, restraining the pulley in a smooth and even manner. Thus mitigating some of the pulsing off the motor.
Also the driving wheels, the pinion, the idler, the driven platter form a kind of gear train who's rotational inertia will produce a flywheel effect to absorb any remaining cogging effect off the motor, and produce a smooth "forward only" driving mechanism.
-Steve
System info @:
http://www.theanalogdept.com/user510.htm
Think you're right about "eddy brake might offer a means of smoothing/filtering out at least some of the cogging effect off the motor" ...If you've played around with different weights of bearing oil, (I'm thinking belt here) you may have noticed that there tends to be a certain 'weight zone' that's right for a given motor & platter.
Too heavy and it's too much, but too light and, even though the actual 'spin' is great, the proper amount of resistance is missing... and there's a stability loss.It seems a similar principle to the eddy current brake. The eddy provides a very graceful, non-mechanical force that operates against the direction of the motor --- a kind of oppositional flywheel effect, in the sense that it doesn't carry the inertia of a rotating rotor but works against it....
And like the 'Goldilocks' proposition of the oil-weights, there's an amount that's just right.
Wonder why beltdrive doesn't use it....
Maybe it can't be used properly against small synchronous motors which wouuld always be trying to get back to their frequency-regulated speed... Not sure.
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