Lathe/Turntable speed stability: Additive or Cancelling Errors?

If we are posting specs, the following are some of the specs for my Teres Certus turntable (in my case the model 450):

My turntable has 60+ pound lead shot loaded platter to the best of my knowledge made of Cocobolo outer wood with a phenolic core

It has Low cogging multi-phase permanent magnet synchronous direct drive motor with:

1) Magnetic damping via eddy current brake
2) High torque capability (563 oz/inch)
3) High resolution digital drive signal synthesis
4) Speeds Supported: 33-1/3, 45 and 78
5) Speed Accuracy:

* 33-1/3 RPM: -0.011% +- 0.003%
* 45 RPM: -0.006% +- 0.003%
* 78 RPM: -0.160% +- 0.003%

Chris Brady does not have wow and flutter measurements for the Certus Turntables but has suggested that they would certainly be substantially less than 0.01%. I do not have any Rumble data.

Rich

So even with this small sampling, it goes to show that turntable specs are many times better than the actual lathe the disc was cut on!

Well, I stand corrected! At least the better TT's are very accurate indeed. I think the vinyl sets the specs, as usual.

Like microstrip, I have plenty of experience with the older, smaller line-referenced motors and they do have issues, but it seems most of the good to best TTs now use synchro control and crystal oscillators.

Thanks folk, still learning after all these years (and plan to do so for many years to come, thank you very much!) - Don

HUGE APOLOGIES TO MICROSTRIP!

Why in heck do I keep calling him Fernando when his name is Francisco!

Sorry bro! I won't make the mistake again. Where's the embarrassed emoticon? I need about a hundred of them right now.

JackD201 said:

HUGE APOLOGIES TO MICROSTRIP!

Why in heck do I keep calling him Fernando when his name is Francisco!

Sorry bro! I won't make the mistake again. Where's the embarrassed emoticon? I need about a hundred of them right now.

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Hi Jack,

I think that you were mixing his name up with flez007 who as I remember is Fernando.

Rich

FrantzM said:

Hi

Interesting that my reference to the cutting lathe became a whole subject of debate. For my own edification. aren't most direct drive TT PLL and can someone tell me why Belt Drive became all the rage in high end circles? Now we even see return of idle pulleys drive which can't be great for noise, wow and flutter or speed stability but these are only objective criteria after all ...

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Hi Frantz,

As Francisco (there got it right!) mentioned, the belt rage started more out of economics. Idlers were expensive to make and DDs much more so. To keep costs down for rack systems and the like belts provided isolation from motor rumble which meant they could use cheaper and noisier motors I'm figuring with less poles and no need for flywheels as in the case of Idlers and complex silent bearings like in DDs. In the vinyl world, all three drive systems have some fanatic defenders. Interesting that Mark should mention the TD-124 as it is both an idler and a beltdrive as the idler is driven by a short belt. If we look at the manufacturers who survived the digital revolution, you'll notice that with the exception of Panasonic/Technics the bulk were small to medium enterprises without the capital to develop silent direct drives. The zenith of direct drive were the Technics and the EMTs, the 950 being the ultimate expression IMO. Without that capacity we find these smaller companies turning to the belt and these split pretty much into two camps, those that resorted to suspension to keep noise down and those that resorted to mass. Both concentrated on getting ever better tolerances for bearings to keep noise down.

With self noise and acoustic feedback below what a rack table owner could have ever imagined, the focus then turned back to speed stability. Why later? Deviations have to be really bad for it to be a deal breaker. Deviations now take on fuzzy monickers which happens every time we reach the limits of our perceptive abilities. Things just get harder to explain because they are both harder to hear and understand. Idlers have "drive", belts have "black backgrounds", I channel Yul Brynner etcetera, etcetera, etcetera. Here we see the belt camp split in two again. Those using AC motors and those using DC motors. Each having pros and cons, and the results going down to execution.

I guess that's it in a nutshell as best as I can explain it

naturephoto1 said:

Hi Jack,

I think that you were mixing his name up with flez007 who as I remember is Fernando.

Rich

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Right! Their avatars are both predominantly brown! Thanks Rich!

fas42 said:

Jack, that's a new one on me. Would you care to explain exactly what's happening here, how it comes about?

Thanks,
Frank

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Hi Frank,

I'm not so sure about the physics and math but it has got something to do with the decreasing radius. Any of our mechanical engineer friends want to help me out here? It was something noticed early on, as early as Edison's cylinder vs. Berliner's flat disc. The cylinder didn't have the problem but the disc won out because it was cheaper to manufacture and store. That and..... tada! .......the change in pitch is small enough not to obsess about.

JackD201 said:

HUGE APOLOGIES TO MICROSTRIP!

Why in heck do I keep calling him Fernando when his name is Francisco!

Sorry bro! I won't make the mistake again. Where's the embarrassed emoticon? I need about a hundred of them right now.

Click to expand...

Right here, Jack: ))

Frank

Yo! Linear velocity. That's the term Lee

http://en.wikipedia.org/wiki/Phonograph

The wiki article mentions it but doesn't explain it. Anybody got a link to something that does?

JackD201 said:

Yo! Linear velocity. That's the term Lee

http://en.wikipedia.org/wiki/Phonograph

The wiki article mentions it but doesn't explain it. Anybody got a link to something that does?

Click to expand...

Sound quality of LPs depend on the linear velocity of the groove - the higher the better. But linear velocity in an LP equates the perimeter of the LP at a certain radius multiplied by the angular velocity in turns per second (33.3/60). In the outer groove this means ~14.5 x 6.28 x 33.3 / 60 = 50 cm/s.
At the inner groove you have 7 x 6.28 x 33.3 /60 = 24cm/s - lower quality. This effect is why 45rpm 30cm records are supposed to have better quality.

I think pitch stability is not affected by radius. Although the linear error due to an angular error changes with radius, the linear speed also changes in the same sense and they compensate each other.

Digital adepts will tell you that CD sounds better because the linear speed of CD is constant - the angular speed is variable - higher at the start of the CD (inner zone), lower at the end.

Hi Francisco,

What are 14.5 and 7 respectively and what is 6.28? The formula shows indeed that linear velocity is affected by change in position. This should change the pitch unless the lathe was made to make compensations right?

Not an engineer here, just curious. I really want to find out the cause of the drift.

It's supposed to decrease as it gets closer to the spindle. A reason some say they hear less highs at the inner tracks. To be honest I never really heard this even if I've been reading about this stuff for years. I guess I'm disqualified from attending any golden ear meetings.

Stylus drag is sort of a sticky subject in other circles. Idler adherents say the lack of slack of an idler is what gives their tables "drive". Belters counter that Idlers are mistaking that sense of drive with subsonic rumble. Direct drive audiophiles are few and far between so they are seldom part of these debates. Strangely enough, when using the same arm and cart on a 301 as a 124 (which as I said has a belt) on plinths made by the same person, it isn't difficult to pick them blind. Clearly drive methods affect sonics. Our own Tony Ky Ma came up with a very novel way to spin his platter precisely to address the bungee effect of belts. A century later and analog is still a mystery. It's perhaps part of the charm. I know it is to me. Technically it's got the deck, no, the entire house stacked against it but it still sounds so darned good when done right.

JackD201 said:

Hi Francisco,

What are 14.5 and 7 respectively and what is 6.28? The formula shows indeed that linear velocity is affected by change in position. This should change the pitch unless the lathe was made to make compensations right?

Not an engineer here, just curious. I really want to find out the cause of the drift.

Click to expand...

I admitted that the outer radius of the LP grooved zone is 14.5 cm and the inner radius 7cm . 6.28 is just 2x PI . As the linear speed is the same at the lathe and the turntable platter at the same parts of the LP (same radius) - you do not need any compensations.

Linear speed at 33.33 at any point of the LP = radius x 6.28 x 33.33/60 cm/s

JackD201 said:

I(...) Strangely enough, when using the same arm and cart on a 301 as a 124 (which as I said has a belt) on plinths made by the same person, it isn't difficult to pick them blind. Clearly drive methods affect sonics. (...)

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Jack, I feel I must disagree with this one. I have owned both turntables. There are so many differences in bearing, platter and structure in those two turntables that I find very difficult that you can associate the difference with the belt drive. Specially as the very short inner belt of the TD124 is used between the rim drive and the motor, not between the motor and the platter. Because of this some people consider the TD124 a rim drive.