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Turntable Speed

I own a Transrotor "Atlante" turntable. I purchased it about 2 years ago with all the available upgrades (platter and tonearm). This unit was $4500.00 without cartridge. It is a belt driven product with an outboard power supply which lowers the incoming voltage to the 18 volts the motor requires. My problem is turntable speed. My 'table speed is about 34 rpms. I could be more accurate if I had better measuring equipment. Anyway, that's about 2% over the correct speed and you can definitely tell the difference in sound quality between 34 and 33 1/3 rpm!. I was a little upset with this revelation and called my dealer about it. I also talked with the dealer's supplier. I received several reasons from these people as to why the speed was not accurate among which was that my power was "out of tolerance." But when all was said and done, none of the given reasons held water and I am now being advised that really there is nothing that can be done. That there is no defect in the equipment and if the speed problem continues to bother me, I should invest $1700.00 in a Transrotor speed controller. As I think over this, I wonder why platter speed is never mentioned or measured and reported on in the reviews for turntables in the major audio mags. (This could be because there isn't any problem, except for my 'table, or there is and no one is admitting it). To my way of thinking, platter speed has to be one of the primary functions of a turntable and that manufacturers would be making sure that their products' platter speeds were within strict specifications. At least better than 2% margin of error as is the case with my turntable.

My question is: Is platter speed error a given in this industry or is my 'table actually in need of repair? And, if platter speed is an industry problem, why are we as consumers paying thousands for equipment which actually doesn't work up to expectations?

frepec

Showing 3 responses by johnbrown

johnbrown
195 posts
 
AC synchronous motors are dependent on the line frequency for correct speed (such as the aforementioned Scout) so I imagine that VPI offering the SDS as an aftermarket accessory (though in reality it's a necessity, since frequency can vary, thus changing the motor speed) is simply a marketing decision to keep initial tt pricing down.

A DC motor, though, should be able to run at the exact speed required every time it's turned on-so with the correct pulley and platter size, and belt thickness, 33 1/3 rpm should be easily maintained, minus the effects of wear, dirt, belt slippage, etc.

Which leads to the possibility that some manufacturers purposely build their tt's to run slightly fast, in order to give a false sense of excitement, and PRaT, to the sound.

This is just a guess-AFAIK, no proof exists-though Rega has long been rumored to employ this technique.
johnbrown
195 posts
 
Dan-ed-

You're right of course-I should have emphasized the theoretical nature of that thought process (-:

Still, with the correct circuitry designed for a specific motor and application, you'd think they could get it right.

To take it a little further, those same DC- motored decks should, if anything, rotate *slower* with the effects of age, wear, dirt, belt slippage, etc., not, as is the case with the OP, faster. Which perhaps gives even more credence to the 'faster by design' theory, especially if the OP's deck is maintaining an always and constant (too high) speed. All theoretical, of course.

Maybe someone who knows a lot more than I about designing run circuitry for DC motors will join in-where's Mark Kelly or Chris Brady when you need 'em? I'm guessing, though, that a manufacturer could pretty easily add speed adjustment to their basic DC circuitry for Very Little Money-that is, if they didn't have an optional Motor Control ready to sell you.
johnbrown
195 posts
 
To VPI's credit, they do give you the ability to (slightly) adjust speed even without a motor controller-the motor pulley on their decks is 'stepped' from a larger to smaller diameter, thus allowing you to move the belt to the pulley diameter that corresponds to attaining the correct platter speed. Credit where due, etc.
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