Hello, I cant seem to find a 33 1/3 rpm motor anywhere for a record player i am going to build. Would a 33 rpm microwave motor work. Are there any websites that sell record player motors that are under 100 dollars? I do not care if it isnt a good quality motor.
the simplest means of motorizing a turntable platter is to use mechanical speed reduction. old cheap turntables used puck drive. that is, the 1800 rpm AC motor had a small drive shaft and an idler puck transferred that motion to the inside rim of the table. the motor shaft was stepped in diameter so that speed change from 78-45-33 was done by sliding the puck. the inertia of the table smoothed out the rotation speed at 78 rpm, but at 33 rpm rumble was a problem. the speed reduction was the ratio of the motor shaft to the inside table rim diameters, or 54:1 for 33.3 rpm. A 9 inch platter would need a 1/6 th inch diameter motor shaft for 33 and 3/8th inch for 78. the next improvement was to use belt drive. the motor still turned at 1800 rpm but the small motor shaft pulled a belt that went around the outside perimeter of the turntable. this worked very good for 33 rpm as the belt filtered out flutter and reduced mechanical rumble. a stepped shaft on the motor was used for speed change to 45 rpm but this did not work so well for 78 rpm where slippage becomes an issue. current technology is to use DC motors and servo speed control. the motor can be direct or belt connected and the speeds are greatly reduced. 33 for direct and 200 for belt drive. the motor has to be multi-pole construction so that speed is absolutely uniform. a sensor detects notches on the rim of the platter for the feedback loop. an advantage of this method is the speed can be deliberately increased or reduced electronically slightly to adjust the playback pitch of the music. and finally such a system is fully isolated from variation in the power line both voltage and frequency.
Motors that weren't originally designed for turntables or tape machines will severely disappoint you. They aren't synchronous, and therefore they don't rotate at a precise or sufficiently constant speed. Turntables with belt or idler drive use synchronous motors that turn at speeds between 300 and 1800 RPM; suitable speed reductions are made by the ratio between the size of the pulley on the motor and that of the drive surface of the platter. The platter must be as perfectly round as possible to make the speed perfectly even. Only direct-drive turntables have motors that turn at the speed of a record.
Unless you are making a direct drive, in which you would use a polyphase digitally controlled motor (like a VCR capstan drive), you get one with a faster very stable speed, and with enough torque to turn a platter. You use a belt or idler to speed it down to the turntable (which has a big ring in it for the belt or idler to mate with. A microwave turntable motor is probably not exaclty 33 1/3 RPM. You need to somehow do 45 RPM as well. Using a belt or idler it is doable, with a multi-step pulley or motor shaft. If you use a DC or polyphase motor you can regulate the motor speed to get 45 or 33 RPM.
High class Record turntable is still available sell in some high class audio amplifier store. Any small quiet AC motor can be used with the help of Variable Frequency Drive to control motor speed.
