Direct drive vs belt vs rim vs idler arm

Interesting how the general question regarding drive implementation has quickly narrowed to a focus on speed stability per single revolution. I suspect that this is because this is one of the most easily measured paramters. It is human nature that people respond to what is being measured and audio is no different. However, this can have untoward consequences. I am old enough to remember when THD was touted as the ultimate measure of amplifier quality but improvements were acheived with increasing negative feedback; ultimately with deleterious effects on the end product.

Single revolution speed stability is clearly important, but, perhaps, this is not the only (or even most) important consideration. As others have alluded, the Timeline only measures accuracy per revolution, not speed changes within a revolution. Theorectically, if the first half of the revolution was 16 2/3 rpm and the second half of the revolution was 50 rpm, the Timeline would be spot on at 33 /13 rpm. I doubt that anyone would consider this a quality turntable.

I supect that the amount of internally generated noise and vibration and ability to dissipate borth internally generated and external noise and vibration are also important to the overall quality of any turntable.

At a certain level of performance, are other parameters more important to vinyl playback performance, i.e. tonearm and cartridge quality?

For the record, I'm not a turntable designer and own a belt drive turntable but would be comfortable owning any number of idler wheel and direct drive tables.

Just to clarify for those not familiar with the device, the Timeline flashes a dot on the wall once per revolution; it is not a continuously illuminated reference point and hence cannot show aberrations occurring in one revolution, but only deviation from a fixed reference point (on the wall for example) over some period greater than one revolution. Jazdoc's point is well taken.

Palasr, I am fairly certain the Timeline flashes more than once per revolution. (I cannot recall the exact frequency; maybe Mosin knows.) Thus it may detect short term speed instability, in fact, altho with what accuracy I cannot know unless I know the frequency.

You would think that the KAB strobe could also hint at short term speed instability, as the "33" would waver or even flicker back and forth while under observation. But I don't know how sensitive it would be to such aberrations.

Mosin/Richardkrebs – thank you for your excellent thoughts on this thread.

Mosin – as just an amateur hobbyist myself, most of what you have said is in sync with what I have heard with my TT’s the last few years. I agree that string drive could be a little fiddly, when trying to convert a belt design TT to thread/string. But I have found that on a string designed TT – once the string technique is learned (there was a learning curve with mine), it was pretty much plug and play after that for me.

RichardKrebs

It was actually possible to recognize the music being played at the time on the scope. The speed sensor was measuring these tiny errors and correcting. This could be observed by watching the motor draw current in sync with the music. An amazing observation.

I find this simply incredible.
Are you able to tell us what turntables / tonearms /cartridges you used during this analysis/testing?

I am now using laser tach to determine my platter speed and stability. IMO, it is the most accurate way to gauge the speed on the platter. Accurate to 1/1000 th of a rpm. Only $200.00. It should be placed on a tripod for the most accurate measurement. Monarch PLT 200.

http://www.omnicontrols.com/detail.aspx?ID=3720