Direct drive vs belt vs rim vs idler arm

I'll take belt drive over the over versions and here is why. First, belt drive tt's in general have high mass platters. That provides not just speed stability but also dampening; dampening not just external vibrations but also motor cogging. The mass of the platter provides inertia to help keep the speed constant. For example, my tt has a 14lbs (6.36kg) platter. A 1 gram change in stylus drag (assuming a drastic change in the record groove) generates 0.00155Nm of torque at the outer rim of the record. Assuming all else is constant except for this torque change, the platter is going to lose 0.29% of its speed in 1 second. Of course the motor is going to increase torque to compensate, but for this analysis you can see the impact of stylus drag on the platter. The deceleration is proportional to platter mass, so if your platter weighs 28lbs, then the speed loss would be half or 0.145%. Conversely, the stylus drag will have a proportionally larger impact on lighter flywheels. Motor speed control and belt compliance play a larger roll in speed stability than inertia, but I wanted to point out the value of higher mass platters. Now imagine a low mass platter directly coupled to a motor. Not saying it is impossible, but it is definitely an engineering challenge to smooth out the torque ripples from the motor and isolate the record from external vibrations.

I would posit that one cannot argue from principles alone that one way to drive the platter is superior to another. I say this, altho I do agree with Syntax that idler drive turntables must deal with the issue he cites. Other drive systems have other issues. Tony, what you claim as a merit of belt drive is also a demerit. If the belt is elastic, then you have speed instability due to that. The big fat platter does provide inertia to minimize that problem. If you have an inelastic belt, then vibration (and cogging?) from the motor have a pathway to the platter, and "belt creep" occurs nevertheless. Any deviation from perfect roundness (or flatness) of the belt also can introduce speed instability. I say all this only to support my opening statement; they are all flawed in one way or another.

I never said that the Linn and Nottingham are the same - I was saying they have the similarity of being low torque designs and sounding excellent 'IN THEIR OWN WAY'. I have to say I was never a Linnie myself, however, I heard one with all the Funk Mods and thought it sounded wonderful - I never thought I would ever say that.

Lewm - he didn't say elastic belt drive, he said belt drive. My silk thread "belt" does not stretch, the ac motor doesn't cog, and I dont get belt creep whatever that is. According to both the Timeline and KAB the speed on my deck is rock steady. I have dispensed with both a 301/401 so I know what those idlers sound like - musical but far far away from state of the art in resolution & transparency.
I agree with you they are all flawed, but which has the least flaws.

Truly, as Rhett Butler said, I don't give a damn.
I respect all of our opinions, and really being happy with one's turntable is all that counts. For me, in practice, there is such a thing as "good enough". The theoretical discussions are a separate bit of play.

For a definition of "belt creep", which is a factor for any conventional belt-drive turntable where the belt travels around a pulley that is some distance from the edge of the platter, go to Vinyl Asylum and search on the phrase. There you will find Mark Kelly's explanation. To a large degree, the phenomenon can be mitigated by having the motor pulley as close to the platter as possible, a la Nottingham, or better yet by having the belt completely encircle the platter, or nearly so. I believe the DPS or Artemis table (one or the other) nearly achieves that by employing a separate capstan. Also, the 47 Labs tt takes a shot at it.