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Thread: Idler driven turntable speed control

  1. #21
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    Quote Originally Posted by muckelroy View Post
    I understand. My changer is based on a 1940s design (possibly earlier) and unlike later pro-sumer and semi-pro turntables, doesn't have a strobe light system or PWM sync for verifying speed. I base my conclusions on the fact that all of my records (ranging from classical/concert music to prog rock, and even one "reference" disc put out by Maxell) sound sharp to my ears, and are playing at keys verifiably sharp compared with something known to be A440 (Hammond organ, and a Yamaha digital piano, yes it's set to A440).
    You know that although concert pitch is A 440, orchestras and bands routinely tune to a higher pitch. You really need a way to either measure the turntable speed or use a recording of known pitch for your evaluation. Having said that, I wouldn't be surprised if your turntable was running slightly off-speed as an accuracy of +/- 2% was considered adequate for consumer units of that era.

  2. #22
    ff Fortissimo muckelroy's Avatar
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    Today the problem is not happening. Odd. Even verified with the same albums I tried playing along with last time, and just to be sure I wasn't completely insane, printed out a strobe pattern disc, and it was still as can be with a 60hz LED strobe on it. (I forgot about those strobe discs, I worked on a Dual turntable that came with one, but didn't even think about the possibility of printing my own out. haha.)

    I'm going to remove my tin foil hat now. Carry on with whatever you were doing, nothing to see here.

  3. #23
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    Quote Originally Posted by muckelroy View Post
    Today the problem is not happening.
    Only synchronous motors are impervious to speed variations due to voltage variations. Again, many consumer grade turntables used non-synchronous shaded pole motors which will drift in speed with line voltage.

    From Wikipedia
    Shaded-pole synchronous motors are a class of AC motor.
    Like a shaded pole induction motor, they use field coils with additional copper shading coils (see the illustration) to produce a weakly rotating magnetic field. But unlike a shaded pole induction motor (which uses a squirrel cage rotor), the synchronous version of this motor uses a magnetized rotor. This rotor rotates synchronously with the rotating magnetic field: if the rotor begins to lag behind the rotating field, driving torque increases and the rotor speeds up slightly until the rotor's position within the rotating field is a point where torque = drag; similarly, if the rotation of the field slows down, the rotor will advance relative to the field, torque will decline, or even become negative, slowing the speed of the rotor until it again reaches a position relative to the field where torque = drag.


    Because of this, these motors are often used to drive electric clocks and, occasionally, phonograph turntables. In these applications, the speed of the motor is as accurate as the frequency of the mains power applied to the motor.

  4. #24
    Moderator Wes's Avatar
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    What speed is your motor supposed to turn at? Perhaps you could replace it with a self-starting Howard motor. My CV has a motor in it that is frequently used in turntables...

  5. #25
    ppp Pianississmo khouji123!'s Avatar
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    I think you need to change the frequency

  6. #26
    ff Fortissimo muckelroy's Avatar
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    For the past few days, the speed has been fine. Not sure what was causing my original problem, and frankly I don't know if I have a synchronous, or asynchronous motor, or whether it's shaded pole or not. Hmm.

    The more pressing problem that I am troubleshooting is completely unrelated. Lack of gain and clarity in one channel. One channel is very dull sounding and primarily sounds like reverb. It's not an amp or preamp problem. I'm not sure if it's my needle, the cartridge, the wiring, or a weird azimuth/phasing problem. This turntable doesn't afford many options for calibration of things like that.

    Thanks everyone for the fun suggestions for the speed issue so far.

  7. #27
    Moderator Wes's Avatar
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    See if it was made in Australia. It might be meant to turn the other way. Does your music sound satanic?

  8. #28
    ppp Pianississmo FDelGreco's Avatar
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    Quote Originally Posted by muckelroy View Post
    For the past few days, the speed has been fine. Not sure what was causing my original problem.
    Maybe your ears were sharp! <grin>

    Frank

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