Cutting vibrations from a (Garrard) synchronous motor.

[hailteflon]

Hi Sreten,

Yes, motor technology can go far beyond what is in a common record player.

AFAIK the shaded pole induction motor would be synchronous if it did not have the shaded pole. It is synchronous with line frequency when not under load.

The fixed speed turntables with AC motor do slip. When they go into the change cycle the RPM will usually drop considerably. Without the shaded pole the motor would lock up when placed under load.

A common ailment in record players is when the platter runs a little slow no matter what is done to bearings, lubricants, etc. This is due to the quality control and materials used in the motor. It has too much slip.

The 50s motors generally are OK, but in the 60s they seem to be using recycled aluminum in the rotors and no telling what other inferior materials that do not age will. The varnish between the rotor laminations may deteriorate, not sure.

The rotor pins can be swaged and this may bring it up to speed. Rust on the rotor can affect RPM as can the lubricant. They slip too much. Sometimes this can be cured by replacing the rotor with one from another motor.

I read about these little motors until I finally found all that I could about bringing them up to speed. There are many tutorials, but almost none of them discuss the rotor laminations. As I recall an induction motor is synchrous by classification. It would have no torque without the shaded pole that
allows it to slip ( drop below synchronous RPM) when under load. Mark

[sreten]

Hi,

I suggest you read up more on motors, I'm not going to argue about the details.

/sreten.

[hailteflon]

You may have some sort of point from a technical terminology standpoint.

Shaded pole induction motors do slip and they are used extensively in changers before the DC motor era began. The nominal RPM is synchronized with line frequency.

My intent here is to help someone who is working on a Garrard motor.

These forums will be archived for decades. I have derived many good pieces of info from forums in general.

I have worked on hundreds of these motors and regardless of some techical flaw in my terminology I am not wrong. I have fixed many of them. Excessive slip is usualy due to excessive rotor resistance. The squirrel cage (rotor pins) has a flaw in it. I said this for those who may benefit from this, not as a target for your ego war.

People usually want changers to play 78s. They are being destroyed due to lack of understanding about how to repair them. When properly overhauled they are not the junk that they appear to be beforehand. The predominant problem with all old turntables and changers is dried lubricant and rotten rubber parts.

You seem to be on a quest to increase the mass of your ego.

I don't want to argue with you. I don't want you to teach me about your delusions of grandeur.

Many competent and potential posters do not participate in forums because of punks like you. A very knowledgable audio engineer told me that he doesn't post because of "flame-o-grams."

This is a well moderated forum. Even so, you have learned to drag an issue into conflict.

[sreten]

Hi,

You misunderstand my post.
The guy is interested in performance. He has a Garrard Zero 100S.
My post was somewhat brusque, I apologise about that.
Seems I do have to argue the point.

It may be true that a synchronous motor in an autochanger slips
during the change cycle but this is not relevant to the question.
What is relevant is the typical "not under load" performance.

To me you are just confusing the issues to someone who is unlikely
to become an expert on the all and sundry of turntable motors.

It isn’t really synchronous because the shaded pole allows it to slip under load.

Under the circumstances of interest this is not relevant, and
from my perspective very misleading. The shaded pole creates
the rotating field at the cost of extra power drawn and heat.
The sort of slip you are referring to applies to all synchronous
motor types under "load", not just shaded pole.

The point of his Garrards Synchrolab motor and the near ubiquitous
4 pole shaded pole motors in far eastern belt drive turntables is they
operate with a slip angle and are synchronously locked to the incoming
AC frequency when playing records, effectively near "no load" behaviour.

(also applies to shaded pole clocks and tape recorder capstan motors)

/sreten.

[sdman]

Anyone ever check the rotor balance on the shaded pole motor.

I think I'll check my Zero 100 to see.

I have a suspicion that the balance is very close.

sdman