Direct drive vs belt vs rim vs idler arm

Lewm - in my posts I have tried to relate what I hear with the design etc. Some folk misread stuff. I am not anti direct drive or any drive. What I have heard in very good systems is that there are very few DD's that dont sound awful, by which I mean grainy, grey, music dissembled, fragmented, a lack of dynamics and transparency. The only ones I've heard that dont sound awful are the SP10mk3 and L07D. The Goldmund I heard had a rebuilt and upgraded power supply, many other upgrades and was in very good state of tune. The standard L07D demolished it - demolished it. Demolished it in terms of speed and timing. The Kenwood sounded more lucid, crisper and cleaner. I use this example to illustrate that in my view if you are running direct drive it needs to be at the level of the SP10mk3/L07D at least or you may be better off with an idler or belt drive. Ironically the Goldmund would probably pass the Timeline test, so the Timeline test is very valuable to give you assurance that the basic speed is accurate and maintained, but then we get into the dirty unknown. What happens in between at the micro level.
I have made a statement supported by physics that the high inertia of the Final will result in deceleration due to stylus lag variation of 1/4 in magnitude of that of the Technics SP10mk3 and Kenwood L07D. Furthermore results that quantified the stylus drag with and without the stylus playing are at a level less than the wow and flutter levels of the Technics SP10mk3 and Kenwood L07D.
A counter argument has been proposed that properly designed servo speed correction is a fundamental requirement for any TT. No numbers or empirical evidence have been put forward.
This is the nub - both the Final and the SP10mk3 are 2 of the best TT's made, they are at or near the top of the tree - so the question is what if you cant afford or obtain the top of the tree? What compromises should you make if you are going to make any ? Most think that what they have is the best. My nature is to try and understand why things sound the way they do. I have been able to improve my system by doing this - understanding what I have, its design construct and selecting products that achieve the goals which for me are important, speed, timing, coherency, harmonic structure. I personally dont have perfect pitch, but I'm extemely sensitive to timing - if the timing is off, I cant stand the music, fall asleep, lose interest.
The posts here that have references to gear I might have heard, hard facts are valuable and enlightening. Recent examples are Halcro's speed testing and Mosins' debate on belt creep which led me to study up previous posts and discussions on vintage idler motors, which was informative. Folk shouldn't get offended by posts - just get pissed off enough to go away and do some research. We all learn from this process.

Richardkrebs :

Let's assume we are tracking at 2.0g.
Now let's break down the stylus drag components into 2 parts - one being stylus drag due to the tracking force ( A ) and the other being the variation in stylus drag due to the variations in the music ( B ).

I measured A, not B.

A - Stylus Drag Due to Tracking Force ( assume constant ).

When you drop the stylus into the groove the high inertia TT drops 0.008%.
( By the way - this was a very conservative estimate to avoid debate, it's actually less )
Now I believe the Technics will drop by 4 times this if the servos are not on due to the lower inertia.
The Technics maintains speed because the servo kicks in.
This is no different to me adjusting the speed via the controller to account for the constant drag...except for the following -
When I bring the speed up to adjust for the 2.0g tracking force I bring it up manually until it the speed is stable.
The Technics servo will react by increasing the speed. The catch here is that the servos only react to errors or changes in load and they dont know the magnitude of whats coming, so they ramp up the response until such time as they detect the speed is too fast - they overshoot. Then they have to correct for the overshoot. This becomes a constant cycle of overshoot and undershoot. You might not be able to measure it, but it is there.

B - Stylus Drag due to Variations in Music

I cannot measure any stylus drag with the high inertia TT. I checked for variations on both inner and outer grooves.
I assume if it exists it is too small to measure.
Same argument exists as in A above, if there is any variation then your DD servo will kick in according to some preprogrammed parameters, and once the servo kicks in, again you end up with micro overshoot and undershoot - too slow, servo, too fast, servo, too slow etc

Now we can argue until the cows come home a to which is better or worse, and which cow comes home first will vary depending on the design and quality of the individual design.

Wow and flutter versus Stylus Drag
I would give equal weight to these. If I am listening to a piano concerto, I want to hear the attack, intensity and decay of each note as well as the ebb and flow of the performance.
I would also suggest that to reproduce the attack, intensity and decay of the note, then the record/platter interface and platter/bearing/plinth design and how it deals with excess energy and maintaing a rigid loop will have a major bearing as well as stylus drag. Certainly the designers of the Final believe there is significantly more energy generated than that required to move the stylus which needs to be dealt with effectively, whilst maintaining a rigid loop between cartridge and record to measure the groove accurately. Removal of this excess energy in my experience is analogous to lowering the noise floor - increased resolution, less smearing of notes.

Re the cogging : I cannot be sure that the instability I heard is cogging. I have described what I heard a the response to Lewm which was posted prior to your last response. It may be the servos, lack of inertia or other issues, but I would add to your comments that cogging can be induced by poor power supply design if the current waveform driving the motor is not maintained accurately as well as the motor itself. I have seen a number of TT's where the power supply regulation is poorly designed and literally turns on and off whilst playing.

Cheers.

Dover I personally would like to know what your main system consists of?

There is a reason for this

Lawrence
Fidelity Forward

I was wondering if someone with two tonearms can do a simple test with the Feikert Android/iphone app. Play the test tone with the first tonearm and begin recording. After some data has been collected, drop the second stylus onto the record and see what happens to the tone. If the app is sensitive enough, this might show how much the platter slows due to the additional stylus pressure, how quickly it recovers, and how much it overshoots. It would be really interesting to do the exact same test on a number of different TTs.

Dover. I tried to get out of this thread by offering an olive branch since I sense that we are going nowhere.... oh well.
The argument that servos cause overshoot followed by a period of slowing and then repeat does not hold up to analysis. This pitch was likely put out into the market by BD manufacturers and it has taken root in the collective thoughts of the audio community.
We use servo control here almost daily on small and large machines. If they behaved as you describe the machine performance would be totally unacceptable in some cases destructive and dangerous. Servos are not fully on, fully off devices. They have response curves, gain, ramp rising and falling, dead band and frequency responce adjustments. These parameters are talored to the task. We tune then for this. Properly implemented they do not overshoot and as we apply then here they achieve a staggering level of accuracy. The same applies to DD and ironically this is proven by the scope tests I did on the Goldmund. You will recall I could see the music being played at the time on the scope, even treble information. If the servo was correcting, over shooting, correcting undershooting..etc, what I would have seen would be a series of square wave like pulses with little relation to the music as the platter acceleration/ decelleration time constant would smother the individual current draw/music waveform. (I have said before. A correct match of motor capability, platter inertia and controller) Say what you will about the Goldmund, but one feature it has is a very mechanically stable speed measuring system. This along with the servo iteslf was doing its job correctly. ( lets keep physical motor cogging out of this)

I hesitate to use the "spurious" word again, but while loop rigity, energy dissipation etc are topics dear to my heart, as you well know, they are spurious to the discussion on platter speed stability.

Wow and Flutter, stylus drag speed change. Yes I knew the moment I pressed submitt that this would draw a response. I will concede that they are both troublesome. That said as per my earlier post, stylus drag induced speed changes are below the threshold of measurement with the SP10 MK3 and most likely many other DD tt's. On the other hand the time line is ineffective in measuring your type B stylus drag because, by its very nature, its effect is transient and the time line is measuring an average.

Agree, quality power supplies are critical to the correct operation of....just about everything in our hobby.

Ketchup. I like your idea of using two tomearms. I think that the test disc is 10 inch diameter, havent seen one. So could it be placed on top of a LP? Use one arm to measure frequency and use the second arm to play music on the outer track of the LP. That would be intersting.