# Driving a Turntable with a Two-Phase, Bipolar Stepper

I'm a relative newbie to electronics, and as an educational project I'm building a record turntable. I'm comfortable with the purely mechanical aspects of the project, but I need some help understanding how to drive the motor.

I have a two-phase, bipolar stepper-motor that I'm trying to use to drive the platter via a belt. The platter will turn once for every six turns of a wheel driven by the stepper. Using a stepper-motor controller in micro-stepped (1/8th-step) mode provides great torque and speed control, but makes the motor much too noisy for this application since the tone arm on a turntable is very sensitive to vibrations.

If the accounts I've read are accurate, a motor like this one can be driven smoothly by applying a voltage sine wave on the first winding, and simultaneously applying a second voltage sine wave (offset 90 degrees) on the second winding. What is the best way to do that? I have found circuit diagrams for op-amp based sine generators which have a synchronized cosine output. Is the task as simple as using a pair of op-amps to amplify the generated signals and then using the amplified signals to drive the motor, or am I missing something that would prevent that idea from working? Is this whole scheme crazy for a reason I don't yet understand?

• And suddenly a thousand audiophiles cried out, and were silenced. – Connor Wolf Oct 18 '12 at 8:10
• For the record, I am not expecting audiophile quality. ;) – PeterAllenWebb Oct 18 '12 at 13:42
• This guy was expecting audiophile quality, and by his account he achieved it: altmann.haan.de/turntable I'd be interested in hearing people's thoughts about his assertion that: "a rare synchronous motor (like the Premotec) is nothin-but the same (in principle and end result) as a cheapo two-phase stepper motor with a step angle of 7.5 deg" – stib Feb 21 '18 at 10:03