Turntable weight affects speed
I tried a Thorens tt weight on my Thorens TD-850 belt-drive tt. It noticeably slowed it down. It seems like extra weight on the bearing would affect any tt, but what do I know? Is a speed control (and strobe/test pattern) generally required to use a turntable weight while maintaining the proper speed?
To add more context to the discussion, the OP’s platter weighs 4kg and the record weight is 291g - a 7.3% increase in mass which is positioned right over the axis of rotation. I highly doubt that very slight increase in rotation inertia is causing the ac motor falling out of synchronous speed. I would look at lubrication and belt wear as the potential cause. |
Assume: Without the added weight the TT platter RPM speed is correct when playing a record. Add the weight the platter RMP speed slows down when playing, listening, to a record. ("It noticeably slowed it down.") Remove the weight platter RPM speed is correct when playing a record. Therein platter is up to normal RPM running speed. My guess is the added weight puts more pressure on the spindle and the bearing it rides on. Therein added friction, drag. I guess if the belt is worn the added friction, drag, caused by the weight there would some slippage around the motor pulley... Slower platter RPM speed. One way to see if the motor RPM is slower with the added weight would be to check the motor pulley RPM speed playing a record without the weight and then again with the weight. If the motor pulley RPM is "noticeably" slower then it is not belt slippage. My guess then would be the "Fully electronically regulated AC" power supply can not supply the added power, (P = I x E), needed to maintain the power and frequency needed for the correct RPM speed of the AC-Synchronius motor. At that point I would not use the weight!
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@clearthinker Please understand that my post here is meant to keep the physics correct and not to embarass you. You have a rudimentary understanding of some physics concepts, just enough to be dangerous, as they say. Indeed, there is angular momentum, which is constant and once accelerted to speed, needs no force to maintain it. It is the acceleration that is different with mass (as I explained). As others have said, belt drives can struggle accelerating to speed, which is why many spin by hand before turning on. Once spinning all the motor has to overcome is the friction of the stylus, the load of the bearing (very low with a precision high end turntable) and losses in the belt and the motor. None of these change with mass. Some might think friction increases with mass. Indeed it does when sliding a mass on an inclined plane for a high school physics problem. But with a precision bearing, there should be negligable difference with the mass added. The exception I mentioned earlier would be a bad bearing that has more resistance to rotation with the increased mass. Jerry |
@jea48 good theory. something is rubbing that shouldn't be rubbing, and with the extra mass, it rubs more. |
