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turntable motor speed

I understand that an AC turntable motor uses the incoming line frequency of 60hz to set the motor speed, but how does a DC motor determine speed and how do you vary the speed to adjust for changes in platter or pulley size. Is the voltage changed and therefore the speed is controlled by the voltage or is there some other method at work. For instance, if I am running a 24vdc motor, would increasing the voltage to 25vdc cause the motor to run faster? Is it important to ensure that the voltage is exactly 24vdc, or is anything close acceptable?
manitunc

Showing 3 responses by manitunc

manitunc OP
795 posts
 
Ok, so what does the feedback regulation do to the motor to change its speed. Does it change the voltage, and if so, how? more for faster? I mean, its fine to say that a circuit regulates the motor, but my question is how does it do that. The motor only has two wires that feed it, so something in those wires is telling it to speed up or slow down. What is it? voltage?
manitunc OP
795 posts
 
there are a number of fancy dc voltage converters that contain an input to run a wire back from the motor to the converter to ensure that the rated voltage is maintained. Would these converters be useful as a power supply for a turntable motor. I have used one as a Sota power supply, but have not attached the wire back to the supply. this is what I am talking about (Acopian B24G210 Power Supply). Some of these supplies are more than $500 new.
manitunc OP
795 posts
 
So the problem is that it doesnt react fast enough to changes in load? I would be interested to see what actual fluctuations exist in load when turning a fairly heavy platter. I would think inertia alone on a 20lbs platter would smooth out any inconsitencies in load quicker and more thoroughly than any motor controller could. The motor itself wouldnt have enough torque to change a heavy platters speed that fast.
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