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| Circuit ideas for Xtal locked AC synch turntable motor drive |
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| djsb:
Hi, I have a turntable (record deck) here at home and would like to explore ideas for driving it's motor electronically. The deck uses an AC synchronous motor that is currently reliant on the AC mains frequency. That's fine and it works OK. I always wondered as a design excercise how it could be driven from a more accurate frequency source like a quartz crystal. I know I would need a crystal oscillator but how would the motor be driven? The AC waveform (50Hz Sine wave) would have to be stepped up to around 240v (or 110v as the motor is rated at if fed through phase capacitors). Maybe a circuit could drive a conventional step down transformer but in reverse? Does anyone have any suggestions or ideas? Thanks. David. |
| joelby:
Would it be safer to replace the motor with something that works at lower voltages? There are some dsPIC chips designed for motor control that may be appropriate, though maintaining a constant speed shouldn't be a very big challenge. |
| djsb:
Hi, Yes that would be something I could look at. There are DC motor conversion kits available for the turntable but they are expensive (classed as high end audio kits like this (which uses the original motor) http://www.cabezon.eu/product_info.php?products_id=126). I'm not worried about the voltage being high. The current motor is cheap and easy to mount. I'd have to do a lot of mechanical mods to fit a DC motor. David. |
| jimmc:
Remember that, except for direct drive, the actual speed of the turntable is dependent on the diameter of the motor spindle (idler) or pulley (belt). Using a quartz drive will not reduce any errors from this source. Jim |
| joelby:
If you attached a rotary encoder sensor to the turntable, you could probably make it pretty accurate. |
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