2. analog
  3. 1301329548

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
marakanetz's avatar
marakanetz
5,473 posts
 
Increasing voltage will cause the DC motor run faster.
It's very important but nevertheless it's a large downside of DC motor that it depends on input voltage. The voltage stabilization circuits should be very precise.
There are motors that have quartz AC generators of a stable frequency.
kirkus
502 posts
 
All DC motors used for such a purpose have a tachometer and feedback regulation circuit that controls the motor voltage. It's most commonly built right into the motor itself (just like a cassette-deck capstan motor) but occasionally you'll find it as a circuit external to the motor.

Simply regulating the value of the input voltage will not keep a DC motor at an exact speed.
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?
More to discover