New Teres Direct Drive Motor Available as Option

Well, John- who would have thought that that humility would be your most endearing character trait? ;~) I'm not a mechanical engineer or a physicist, but wouldn't torque mostly be an issue in terms of coming to speed from a stop? Once turning at relatively constant 33 or 45 or 78 rpms, wouldn't there be very little torque necessary to overcome stylus drag. I ask this as a serious question, based on my perception of torque as an attribute of a motor that contributes to its ability to accelerate from a stop or at least from low rpms, as in a drag racer from a starting line, where torque at low rpms is just as important as total horsepower at high rpms.

Swampwalker, I don't want to wade into an argument about belt drive vs idler drive vs etc, but "torque" is defined as angular force. So, torque is the product of mass multiplied by acceleration, like any other force. Then, if stylus drag could be thought of as the equivalent of a force that delivers "negative acceleration" to the platter, a high torque motor might be of benefit in overcoming it. The question you raise is however a good one which I have not seen addressed; just what in fact is the magnitude of the force we describe as "stylus drag"? I dunno myself. I think it's key that stylus drag is constantly varying during different musical passages. That's where idlers may have a real advantage, by offering relative immunity to minute changes in platter speed that might other wise result from stylus drag.

Jean,

I think I understand your comparison of idler drive to belt drive, but I'm lost in your comparison of idler to Verus rim drive.

I would think the comparison of rim drive to idler drive boils down to the relative compliance of the interface between motor and platter. With rim drive there will be speed instability if the rubber ring around the transmission wheel has excessive compliance. Is idler drive really much better in this regard?

There is also the matter of transmission of motor rumble. But as with your replinthed Lenco, noise problem can sometimes be engineered.

The torque necessary to meet the changing force of stylus drag is far less than what is necessary to lift an 80 lb. plinth. But it is nice to know that a Lenco motor could be used to drive an electric bicycle.

Don't forget there is also the benefit of high platter mass to counteract the negative acceleration. It is the weight of that spinning flywheel that stores energy and helps get the car off the line. Too heavy, the car is slower to build rpms. Too light, and the car doesn't leave as quickly. The whole system should be analyzed, not just the individual parts. Relative to those light-weight cast or stamped metal tables of the earlier idler/rim drive 'tables the Teres platters are 3 or four times the weight. As Swampwalker said, the high torque may be great for getting the platter spinning from stop but once the platter is at speed, how much torque is needed to maintain constant speed? Which is a state of near zero acceleration. The energy stored in a 30 to 40 lbs platter is helping a lot. The connection of the LP to the platter must also be considered. It does no good if the platter is marching along but the LP is slipping on the surface.

"by offering relative immunity to minute changes in platter speed that might other wise result from stylus drag"

I would agree with that. IMO, this is also why the mylar belts are superior to all other belts I've heard. They don't stretch at all. However, they can slip ever so slightly and that is where the door is open for the possibility of rim drive. Obviously, the next step up should be direct drive, and it goes without saying that every drive systems needs to be well implemented.

Stylus drag – real or myth?

Some time ago I did an experiment to determine just what effect stylus drag would have on an LP. I used a DL103 set to 2.5 gram tracking weight and used a regular 120 gram LP on a cheap mat felt mat (I believe off one of my old Regas). I made a small notch in the edge of the record and aligned it to a piece of tape on the platter. Looking up the edge of the tape (akin to looking down the sights of rifle) I could line up the notch in the LP very precisely.

The one side of the record was played (approx 20 min). The record was unclamped.

Now if the average groove speed is about 14.1 inch per second (20 inch per second on the outer grooves, 8.3 on the inner most groove), that means I am looking at about 1410 feet (16920 inches) of groove length.

After playing, the record shifted at the very most, not more than 1/64 of an inch. That means that over a period of 20 minutes and distance of 16920 inches, stylus drag amounted to only 1/64 of an inch of record slippage; or stated differently 9.235e-5 % slippage.

I did not bother to measure/calculate and compare the amount of drag needed to slide the unclamped LP on the felt mat vs. the drag need to overcome the rotational inertia of a 12 pound platter (never mind the 30 plus lbs Teres platters). I simply cannot buy into the idea that the force of the rotational mass of a platter would be less than the force required to make a 120gram LP slip.

I have not heard a Teres as yet, but I did own an idler wheel (TD124). The idler wheel had no more speed stability than any of my AC motored belt drive turntables.

Regards
Paul