I think the earliest version of the 301 did use a grease lubricated bearing which then became the eddy current brake that RB describes. 301 aficionados may correct me if I am wrong. Some 301 cognoscenti seek out the grease bearing version ahead of the later version.
How important is low W & F performance anyway?
I recently completed work on a direct drive motor controller for a turntable mfr with IMHO, rather impressive results (0.004% 2 sigma method, 0.002% RMS). In measuring other tables actual performance (vs published specs) I was shocked at the rave reviews two tables received that have rather lousy measured performance (but impressive specs). It made me wonder whether the goal of ultra low W&F performance was really necessary? I trust the measurements as they were verified by several methods and software tools and they correlated rather closely, yet the reviewers almost universally praise these tables. It made me wonder if the reviewers even know what they are hearing or listening for and not to put to fine a point on it, does it even matter?
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With regard to the Garrard 301, it has always been my understanding one of the purposes of the eddy brake was simply to load the motor and push the operation of the motor higher up the torque curve. One would assume that it would increase the resistance to stylus drag, but obviously does not eliminate speed variations. |
This is what I addressed in my previous post. Why would it change the resistance to stylus drag? Unless the brake is operating close to the stall torque where the curve is starting to flatten any changes in drag (torque) will show up as a change in speed. |
I recall reading some years ago, in one of the English hifi mags, in an article about the Garrard, the torque curve was published, and the suggestion was that the motor was pushed into operating at a point at which the torque curve was flattening off. This is where I got my understanding around the eddy brake. |
@dover The torque curve is shaped like a sine wave with minimum torque at 0° and maximum torque at 90°. With no load on the motor, the rotor and magnetic fields are aligned (0° lag); as the load increases, the rotor will start to lag the magnetic field as it delivers torque to the load, creating an electronic torsional "spring". If the rotor falls behind the field by more than 90°, the torque produced actually decreases as the load further increases, the "spring" breaks and the motor will stall. At low torque levels the angle is small and the relationship is nearly linear on the slope so small changes in drag will produce an almost linear drop in speed. You are correct that pushing the static load up the curve will eventually reach a point where small dynamic loads will produce smaller changes but for that to be really effective means you are operating close to the stall torque which I doubt is the case. But in theory, you are correct in your understanding. That at least is my understanding, but feel free to correct me if I'm wrong. |
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