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I recently got a Technics turntable and the belt that came with it is super crappy and makes the platter hickup when it passes by the seam on the belt. This is not audible, but it got me thinking about ways that I could control the speed of the platter.

Since it is a technics table it has a little strobe and markings to looks at which are awesome, but "totally the 70s". Along with replacing the belt I started thinking about adding some 21st century technology to my turntable.

  • Adding an Arduino equipped with a light sensor and a speed controller.
  • New brushless motor
  • New belt :)

My goal would be to use the light sensor with the markings that the strobe method currently utilizes to give the Arduino a reading of the speed. With that information I would apply a PID algorithm to control the motor that is spinning the platter.

My question is: would this work? And please tell my why this would be a bad idea if not.

Sponge Bob
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  • The cheapest and easiest way to reduce velocity flutter in a turntable is to simply increase the platter mass. There are custom audiophile turntables out there where the platter can weight more then 50 pounds! – Connor Wolf Jan 30 '13 at 21:41
  • The "hickup" is not audible, so it seems to me you're done without adding anything to the turntable. – Olin Lathrop Jan 31 '13 at 16:37

2 Answers2

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Ooooh fun! An audiophile question!

Now, a lot of this depends on the particular turntable you have.

Anyways, since you stated that your turntable is belt-driven, by far the easiest way to reduce your velocity flutter is to simply increase the mass of the record platter.
Realistically, if the record platter is less then 1/2 a pound, I would honestly recommend you simply get a better turntable.

Most turntables tend to have AC synchronous motors. Now, using an arduino, you're not likely to be able to get significantly better velocity flutter without replacing the oscillator crystal on the arduino.

Realistically, for an application that requires a purely analog velocity servo, "21st century technology" really has nothing to add. Throwing a microcontroller at the situation just increases the complexity, without actually improving the eventual performance. I can pretty much guarantee a well-designed simple analog PLL-based velocity loop will kick the MCU-based velocity controller's ass unless you invest many hundreds of hours into the software in the micro, and even if you do, you'll at best achieve parity. The MCU won't be able to do better, merely just as good.

Realistically, I think the most readily achievable improvements to your setup are going to be mechanical. Reworking the electronics will be both very involved, and not likely to yield improvements.

Many (somewhat crazy) Audio nuts have built custom turntables with platters that can weight 50+ pounds!
Browing the google image search for "Audiophile turntable" is always amusing.
enter image description here

Connor Wolf
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Well, yes, you could make it work that way. As noted There are audiophile solutions to this as well.

As a pro DJ in the 90s, we depended on our technics 1200 turn-tables. The difference was they were direct-drive and didn't use belts.

What I liked about those visual markings: they combined with your human eye scanning frequency visual system frame rate, (~12Hz) and depending on which row appeared to spin forward, stopped, or backwards (wagon wheel effect), you knew the speed of the drive. Came in very handy if you were about to load a 45rpm dance record at 33rpm. For me, it was a good marker as well for beat-mixing.

Back to your question: for 21st century update (assuming you count vinyl in, as you should), you might like to use a direct-drive method, a stepper motor and possibly an encoder (your arduino?). Though clocking the motor at 33 or 45 will mean that record plate will follow (by the time the track starts).

MandoMando
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    "Human eye scanning frequency"? – gbarry Jan 30 '13 at 23:16
  • That's just straight up misconception. The human eye doesn't see in a "frequency," there's no framerate or refresh rate for the human eye. The reason you could tell the speed of the drive is because the light shining on the edge of the table was flashing at the frequency set by the operator's choice of media (if you selected 45rpm vs 33.3rpm, ect). It's a strobe effect. Related uses of a strobe effect is for tuning instruments: http://en.wikipedia.org/wiki/Electronic_tuner#Strobe_tuner – Shamtam Jan 31 '13 at 04:56
  • However, +1 for direct-drive. My DJ friend swears by the direct-drive Technics 1200s he has, and I can see why. – Shamtam Jan 31 '13 at 04:57
  • @shamtam it is more complex, however the human eye does see in distinct frames to the sense that jet engine blades appear stopped at a certain rpm (no strobes required). Even the birds suffer from this and that's why there's that swirly in wing-mounted jet engines. (this is from a Rolls-Royce facts book, but you can check the wagon wheel effect link again) – MandoMando Jan 31 '13 at 14:31
  • Ahh, yes. I thought about going direct drive, myself, but since I was using it for listening purposes and not DJing, I didn't want to hear the hum of the motor. – Sponge Bob Jan 31 '13 at 18:37
  • That was not my edit. Not sure how edits are attributed. – gbarry Jan 31 '13 at 18:53
  • I'll have to assume that "human frame rate" is 12Hz in the States, while it will be 10Hz in the UK. I would also expect that after a cup of strong coffee, the frame rate could go as high as 16Hz. Our home movies were 16fps. – gbarry Jan 31 '13 at 18:59