Stepper driven Turntable

pjrebordao

Senior Member
After coming across some DIY efforts at building turntables, I too decided to give it a try...

I went for an all aluminium construction and a decidedly "mechanical" look. The frame consists of 2 aluminium sheets strongly bolted together, and the platter is a "sandwich" of aluminium-acrylate-aluminium epoxyed together for some vibration dampening.

For the drive I went for what I believe to be an original path. A bipolar stepper motor drives the platter through a toothed belt (to prevent slippage) at a 3:1 ratio.
Typically, steppers are not known for a smooth motion which is absolutely critical here. However, the stepper is driven by a special purpose Toshiba chip that generates two "pseudo" sinuswaves 90 degrees apart, to drive the stepper coils, thus avoiding any vibrations.

A Picaxe 28X1 controller running at 20Mhz provides the timing inputs to that chip with the required precision, both at 33 and 45 rpm. Those timing inputs are generated by Settimer interrupts with a "light" service routine. At 45rpm, there's roughly an interrupt every mS.

Finally, the tonearm is a temporary affair salvaged from an old Sanyo unit.

After a lot of tuning and tweaking, the audible results are quite good with no noticeable wow/flutter. Only a slight low frequency rumble can be heard on the most quiet parts. Probably vibration coming from the bearing, that I’m still hoping to damp.
 

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