Turntable weight affects speed

I tried a Thorens tt weight on my Thorens TD-850 belt-drive tt. It noticeably slowed it down.  It seems like extra weight on the bearing would affect any tt, but what do I know?  Is a speed control (and strobe/test pattern) generally required to use a turntable weight while maintaining the proper speed?


It just may not have the power to haul the extra weight. Is the belt clean / new? Have you tried giving the platter a hand in spinning up to speed?

Agree with @noromance.


From the manual:

TD 850
Drive System: Thorens Belt drive
Motor: Fully electronically regulated AC-Synchronius motor

If the belt is clean/new and the bearing is lubed then the problem could be the added load on the AC motor and or regulated power supply caused by the weight.

FWI, Increase the load on an AC motor current goes up to maintain HP, speed. Current adds heat both to the motor winding as well as the "Fully electronically regulated" AC power supply. (The speed of a AC-Synchronius motor is controlled/maintained by the AC frequency.)


How heavy is the weight?

My weight (TD125 MkII) is a 45 adaptor attached to the flat side of a medium-small brass Mapleshade cone (3 tiny spots of poster tack) and the total weight is approx. 8 ounces.

The DIY weight is as symmetrically balanced as I could get it (pretty easy as the flat side of the cone is the same shape/size as the 45 adaptor) and it’s non-magnetic.

I’ve tried heavier commercial weights with various mats and the 8 ounce unit is all that is needed as I heard no improvement with heavier weights (sometimes the opposite - mine is a "sprung" design).

I did not experience speed problems though within the weight range I experimented with.

I was initially concerned about increased main bearing wear and strain on the motor with heavier weights.






If the weight is too much, try a clamp, like the SOTA clamp.  It really improves sound quality, particularly clarity. 

The weight is 291.6 grams.

so, @jea48, the speed should not have been affected by additional weight?  The power supply (claimed to maintain exceptionally accurate speed - designed by the Acoustic Signature designer - they seemed to use the ps on platters of various weights) should have just increased its current and maintained the speed?  So this was probably caused, as @noromance suggests, by belt slippage?  

it’s an unsprung, 46 lb tt, eliminating vibration sufficiently was a challenge; I thought a weight might contribute to the solution

The weight is 291g (10.25 oz).

the tt was designed by Acoustic Signature, and is very similar to theirs, at the time. AS sells weights c. 280 g.  So it seems like the ps should be adequate.  Unless… the weight is c. 1 oz too heavy?

so if I understand correctly, @jea48 explained that the ps should just increase current to maintain the speed.  So @noromance must be right, it has to be belt slippage? - which shouldn’t happen.  That belt is small and flimsy


Hand spinning will get it up to speed. Once up to speed, the load on the belt/motor should be the same with or without the weight (physics). If it is different, then you have something dragging or a bad bearing that results in extra frictional force exacerbated by the weight.

I asked someone at pro-ject if I could use the same weight I use on my VPI Classic on the carbon TT and he said NO, too heavy for that TT. So, yes. Not every TT is built to handle those weights.

I have a clamp from, Mitchell (I think) that's made for Regas and it's a spindle grabber...on a Linn...works great and will keep the record on there in a strong windstorm. Seriously, you don't want your vinyl to blow off the table although I suppose you could simply close the window.

Since the record weight is positioned over the axis of rotation, the added mass does not substantially affect platter’s rotational inertia, therefore, your motor should have sufficient torque to start and maintain platter speed. 

@carlsbad2     "the load on the belt/motor should be the same with or without the weight" (INCORRECT physics). 

You are possibly thinking of Newton's Law of conservation of momentum.  But if the platter is spinning and you cut the power, it won't spin forever.  Ergo it takes power to keep it spinning.  How much power?  I clearly takes more power if the platter + record weight is heavier as the moment of inertia is greater.  Pace @testpilot , the point you make is correct but there will still be more inertia and this may be sufficient to prevent the motor on the Thorens keeping it moving at the same speed.

Yes, check out the motor, belt and clean and re-oil the bearing

Belt drive players are not designed for extra weight on them.  Oh, they will handle 200 gm records just fine, I mean extra weight.  Something to be said about record camps, too.  If you are seeking smoothness, fine.  For one who wants any "jump factor" forget it.

Try the "Origin Live Gravity One".....You will be amazed at the improvement in all aspects of the sound quality in particular soundstage and instrument separation as well base definition. Just my 2 cents and I do have heavy weights too so I can actually compare!


To add more context to the discussion, the OP’s platter weighs 4kg and the record weight is 291g - a 7.3% increase in mass which is positioned right over the axis of rotation.  I highly doubt that very slight increase in rotation inertia is causing the ac motor falling out of synchronous speed. I would look at lubrication and belt wear as the potential cause.  


Without the added weight the TT platter RPM speed is correct when playing a record.

Add the weight the platter RMP speed slows down when playing, listening, to a record. ("It noticeably slowed it down.") Remove the weight platter RPM speed is correct when playing a record. Therein platter is up to normal RPM running speed.

My guess is the added weight puts more pressure on the spindle and the bearing it rides on. Therein added friction, drag.

I guess if the belt is worn the added friction, drag, caused by the weight there would some slippage around the motor pulley... Slower platter RPM speed.

One way to see if the motor RPM is slower with the added weight would be to check the motor pulley RPM speed playing a record without the weight and then again with the weight. If the motor pulley RPM is "noticeably" slower then it is not belt slippage. My guess then would be the "Fully electronically regulated AC" power supply can not supply the added power, (P = I x E), needed to maintain the power and frequency needed for the correct RPM speed of the AC-Synchronius motor.

At that point I would not use the weight!



@clearthinker Please understand that my post here is meant to keep the physics correct and not to embarass you.  You have a rudimentary understanding of some physics concepts, just enough to be dangerous, as they say.

Indeed, there is angular momentum, which is constant and once accelerted to speed, needs no force to maintain it.  It is the acceleration that is different with mass (as I explained).  As others have said, belt drives can struggle accelerating to speed, which is why many spin by hand before turning on.  Once spinning all the motor has to overcome is the friction of the stylus, the load of the bearing (very low with a precision high end turntable) and losses in the belt and the motor.  None of these change with mass.

Some might think friction increases with mass.  Indeed it does when sliding a mass on an inclined plane for a high school physics problem.  But with a precision bearing, there should be negligable difference with the mass added.

The exception I mentioned earlier would be a bad bearing that has more resistance to rotation with the increased mass.


@jea48 good theory.  something is rubbing that shouldn't be rubbing, and with the extra mass, it rubs more.

@carlsbad2    So you think your turntable will spin forever, regardless of how heavy it is, without any further energy applied to it.

Welcome to the world of perpetual motion.

Rudimantary?  Huh.

...another take.....if your t/t is belt driven and getting on, the belt may have stretched.  

Thanks for all the well-considered responses!  I’m planning to try the Origin Live Gravity One @mgolpoor recommended. 

And, to cover as many bases as possible, I’ll order a new belt. 

A new bearing/turntable… not today. 

trying to be more diligent about updating threads.

Further research located an old review of this tt by M Fremer which said there is an internal potentiometer for adjusting speed.  It was not referenced in the manual. So I bought the RPM Pro app, opened up the power supply box, made some adjustments: problem solved.
  But went ahead and ordered a belt and OL tt “weight”.  The app said the wow and flutter was .25, a little higher than desirable. 

Thanks to Michael Fremer and all the ideas on this thread.

But aren't you just increasing the speed (power to the motor?) to compensate for the additional load? I wonder if that will overdrive/overheat the motor and impact its longevity. 

Agreed, increasing the load might be detrimental. Lightweight Origin Live “weight” is on the way. 

thanks for all the ideas.


On belt replacement, 

I use two belts on my table. Every six months or so I drop them into a pan of boiling water for about twenty seconds, this "un stretches" them a bit. After drying, they go into the zip lock with baby powder in it, then shake them off and re install. I get a lot more life from them this way.