The necessity for absolute tt speed control

[spiritofmusic]

Btw Bill, just about to order the Roadrunner tacho.

 

[Lagonda]

Btw Bill, just about to order the Roadrunner tacho.

How did you hear about that wonderful contraption Marc ? I just checked our PM’s, we talked about the Roadrunner first time in 2017, it’s about time you get one !

 

[spiritofmusic]

Very true Milan. I always try to come good in the end.

 

[bonzo75]

How did you hear about that wonderful contraption Marc ? I just checked our PM’s, we talked about the Roadrunner first time in 2017, it’s about time you get one !

This is funny you went back and checked when he first mentioned it

 

[Lagonda]

This is funny you went back and checked when he first mentioned it

There was one for sale on Audiogon, with a Falcon power supply, i suggested we go 50/50 as i already had the Roadrunner. I realized i needed the Eagle not the Falcon and we did not buy it. They where impossible to get back then. I just realized that was when i first started talking with Marc, big mistake

 

[Lagonda]

We have one PM thread going that is 150 pages long, that coronavirus did make some strange bedfellows

 

[Phoenix Engineering]

Bill, what kind of toque and consumption does the motor/controller you put together for SOTA have ? Will i drive a 100lb platter on an air bearing ?
https://sotaturntables.com/product-category/eclipse-series/

The BLDC motors have 2-3x the torque of their AC synch equivalents, so it should be OK. Also, the motor starts the platter at ~5 RPM and ramps up to 33/45/78 so the torque requirement is much less than a motor that spins up to speed instantly.

 

[spiritofmusic]

We have one PM thread going that is 150 pages long, that coronavirus did make some strange bedfellows

"What's Best PMs"

 

[Phoenix Engineering]

Btw Bill, just about to order the Roadrunner tacho.

Would be curious to hear your impression of it after you've had a chance to use it.

 

[Lagonda]

The BLDC motors have 2-3x the torque of their AC synch equivalents, so it should be OK. Also, the motor starts the platter at ~5 RPM and ramps up to 33/45/78 so the torque requirement is much less than a motor that spins up to speed instantly.

Thank you Bill !

 

[tima]

Oh Tim, one always considers alternatives. This is high end audio. But I so love my sound off lp, that I'm really not motivated.

Tim,

What do you consider a minimum specification for "accuracy" in a turntable?

Sorry but I can't understand why anyone should consider another turntable before discussing a few numbers ...

I know you like formal specifications. The RIAA specifications for an LP associate to 33-1/3 rpm. I've not seen any alternative, have you?

As to your second sentence - no need to apologize. I tried eliciting numerical information from Marc about his upgraded drive system proposal. Some believe one does not need numbers to consider upgrading any component, though many consider cost.

 

[spiritofmusic]

Tim, I don't have any info to give. The new speed controller is in the early days, and the engineer is being a little cagey. I know he's predicting way better than the 0.3% my current unit is specced at.
But as my current designer said, all the options they tried that used a feedback loop to lock better than 0.3% killed the bass and made the sound greyer.

 

[tima]

Tim, I don't have any info to give. The new speed controller is in the early days, and the engineer is being a little cagey. I know he's predicting way better than the 0.3% my current unit is specced at.
But as my current designer said, all the options they tried that used a feedback loop to lock better than 0.3% killed the bass and made the sound greyer.

Yes, I understand - no worries. My point to micro was that we can discuss the topic without numerics.

 

[microstrip]

Phoenix, I believe the latter phenomenon may be the case in my situation. I'm playing albums w some strobe-indicated drift or shimmer, and then corrected, and struggling to hear any difference. Below my audible threshold it seems. However, put a musician in my seat with absolute sensitivity to pitch variation, and satisfaction may drop.

Someone should get some different pressings of the same LP made in the UK, US , Japan and other countries. I would be very curious to know about their speed difference, particularly if the source is analog tape!

 

[Catcher10]

Great thread topic, good info here. My question is what is more important to focus on.....holding 33.3333333333 or holding a 3150Hz tone?
Using the speed controller I have to help hold a 3150Hz tone does not show me 33.33, rather about 33.31. With a good portion of my record collection from the tape era, how can we be sure both the tape deck is on speed on recording and the cutter platter always being 33.33?
Does it make a difference to focus on one or the other?

Thanks everyone!

 

[spiritofmusic]

Throw in eccentrically pressed discs...ie off centre spindle holes...
Great comment, btw.
I'll see where my new Roadrunner sits re 33.33 and 33.31.

 

[Audiophile Bill]

Throw in eccentrically pressed discs...ie off centre spindle holes...
Great comment, btw.
I'll see where my new Roadrunner sits re 33.33 and 33.31.

Has it arrived, Marc?

 

[spiritofmusic]

Unlike our Roadrunner from the classic cartoon, not yet.
"Beep beep"

 

[Mike Lavigne]

what i think....

In order to pick up sound accurately from the analog disc, the rotation of the platter must be rotated at a constant speed without any “fluctuation”. In general, accurate rotation is obtained by servo control by negative feedback, but at the micro level, if it rotates or becomes faster, it detects it and slows it, and repeats the operation to make it faster if it gets slower. Although this level and cycle are determined by the gain of the control system and the loop speed, the period of the speed control of the platter which is the mechanical system surely comes into the audio band. In general, accurate rotation is obtained by servo control by negative feedback, but at the micro level, if it rotates or becomes faster, it detects it and slows it, and repeats the operation to make it faster if it gets slower. If you try to measure a period with a small level, you can not measure the instantaneous state, so you measure the average value. Therefore, fine vibration generated by servo control can not be measured by the measuring instrument, it depends on the human ear.

.......my ear likes steady as she goes....

 

[Lagonda]

On a well designed TT you can keep speed with very little variation without a feedback loop.