Tenkte bare jeg skulle dele med dere noen betrakninger om emnet fra en platespiller konstruktør.
(Har fjernet det som har med produsentens egne spillere å gjøre for å få en mest mulig nøytral fremstilling).
Kommentarer?
To be sure that we are on the same page I do not like the more typical single phase AC motors.
They by design have a great deal of cogging, no matter how they are driven or what tricks are used.
The best DC motors have nearly an order of magnitude less cogging than a single phase AC motor.
Having said this I think that AC synchronous motors have several major advantages over a DC motor.
First a DC motor must have some sort of servo mechanism to keep the speed constant.
This means that the controller is always making speed corrections.
An aggressive correction algorithm will make abrupt changes causing hunting. This is comon with 70s vintage turntables and sounds bad.
Another solution is using a very slow adjustment algorithm that allows for more absolute speed error, but makes very slow and gradual corrections that are less audible.
However, in my experience the speed constancy issues with DC motors are far easier to live with than the cogging from a single phase AC motor.
AC synchronous motors also have a major advantage in the way that they produce torque.
Apply more load to a DC motor and it simply slows down a little.
A fast servo will respond after the event and make a correction that will almost always overshoot and then make another correction.
Not a good situation. A slow servo just allows the slowdown and then makes slow corrections if needed. Better but not ideal.
On the other hand if you add more load to an AC motor he phase angle increases slightly causing the motor to generate more torque instantaneously.
An AC motor is able to exert significantly more torque to counter act small variations in speed due to stylus drag.
This is why AC motors are generally thought to have better PRAT.
It should also be apparent that this benefit is largely negated when an AC motor is connected to the
platter by a stretchy rubber belt.
So unfortunately the significant advantages of an AC motor end up being mostly lost in a typical turntable where a rubber belt is needed to isolate cogging problems.
Og så ligger det vel kanskje i kortene at nevnte produsent har sin egen løsning på problemene ;D
Men ikke at det nødvendigvis gjør ovenstående betrakninger mindre gyldige av den grunn, eller.....?
(Har fjernet det som har med produsentens egne spillere å gjøre for å få en mest mulig nøytral fremstilling).
Kommentarer?
To be sure that we are on the same page I do not like the more typical single phase AC motors.
They by design have a great deal of cogging, no matter how they are driven or what tricks are used.
The best DC motors have nearly an order of magnitude less cogging than a single phase AC motor.
Having said this I think that AC synchronous motors have several major advantages over a DC motor.
First a DC motor must have some sort of servo mechanism to keep the speed constant.
This means that the controller is always making speed corrections.
An aggressive correction algorithm will make abrupt changes causing hunting. This is comon with 70s vintage turntables and sounds bad.
Another solution is using a very slow adjustment algorithm that allows for more absolute speed error, but makes very slow and gradual corrections that are less audible.
However, in my experience the speed constancy issues with DC motors are far easier to live with than the cogging from a single phase AC motor.
AC synchronous motors also have a major advantage in the way that they produce torque.
Apply more load to a DC motor and it simply slows down a little.
A fast servo will respond after the event and make a correction that will almost always overshoot and then make another correction.
Not a good situation. A slow servo just allows the slowdown and then makes slow corrections if needed. Better but not ideal.
On the other hand if you add more load to an AC motor he phase angle increases slightly causing the motor to generate more torque instantaneously.
An AC motor is able to exert significantly more torque to counter act small variations in speed due to stylus drag.
This is why AC motors are generally thought to have better PRAT.
It should also be apparent that this benefit is largely negated when an AC motor is connected to the
platter by a stretchy rubber belt.
So unfortunately the significant advantages of an AC motor end up being mostly lost in a typical turntable where a rubber belt is needed to isolate cogging problems.
Og så ligger det vel kanskje i kortene at nevnte produsent har sin egen løsning på problemene ;D
Men ikke at det nødvendigvis gjør ovenstående betrakninger mindre gyldige av den grunn, eller.....?