The necessity for absolute tt speed control

[microstrip]

(...) A strobe disc is better than no strobe disc, but I consider it a very gross level measurement because it is based on how stable is your electricity from millisecond to millisecond and based on the acuity of our visual perception to detect absolute dead stop movement of the strobe markings. Turn away and look at an object you know is not moving - do you have the same sense of certainty with the strobe markings? Be that as it may, I'm confident you will hear the difference if the implementation is right.

We disagree on this one. Properly used a good strobe is more than enough to calibrate a turntable. Although we have sites giving us the exact frequency in Europe with five digits - all our grid networks are synchronized - we can get a LED quartz pulser for less than 20 euros. As I type the frequency in my house is 50.003 Hz. https://www.mainsfrequency.com/

Exact accuracy of turntable speed is an audiophile overkill - sound quality does not depend on it with a reasonable range. However the ear is extremely sensitive to speed variations - a system with better accuracy can have less speed variation and can be perceived as better sounding or as poorly sounding is the accuracy mechanism introduces variations that we do not enjoy.

As always, all IMHO, YMMV.

 

[spiritofmusic]

If i read between the lines your designer seems to have chosen an unregulated PS. Hmmm, never tried this, but it is an interesting suggestion. It clearly makes the average speed even more prone to fluctuations. Do you know what motor is being used?

Maxon, I believe.

 

[Vienna]

Something i am willing to bet you won't like much.

There is a wide spread misconception that it is a kind of a DC motor. It is not. In the majority of tt applications it is controlled by pure sinewaves as if it were a normal synchronous AC motor . The original design brief assumed a trapezoidal drive, which was externally powered from a DC source.

Tried several BLDC motors, one of which from a Continuum, but none could reach the musicality of a cheap brushed Maxon or an outer rotor Papst. Yes, excellent speed stability but also a substantial and undesired in my system transformation of sound towards greyness.

I hear you analogsa, but I have a complete different sound experience from maxon motors. Side by side with Anaheim motors the sound for, the later was clearly better. unfortunately don’t have experience with Papst motors, however I have heard and read so many positive comments for them and especially for the model used at AS2000

 

[microstrip]

I hear you analogsa, but I have a complete different sound experience from maxon motors. Side by side with Anaheim motors the sound for, the later was clearly better. unfortunately don’t have experience with Papst motors

You should get an used Studer/Revox capstan Papst motor, IMHO a serious large and heavy motor with an well designed outer rotor that doubles as an enormous flywheel.

 

[Vienna]

You should get an used Studer/Revox capstan Papst motor, IMHO a serious large and heavy motor with an well designed outer rotor that doubles as an enormous flywheel.

Unfortunately I couldn’t source one in good condition.

 

[microstrip]

Unfortunately I couldn’t source one in good condition.

Typical prices for used very good condition Revox capstan motors are around 60 euros, the Studers are more expensive - I paid euro 180 plus postage (these beasts are very heavy) for perfect Studer A810 capstan motor. The shaft is as new, I felt guilty of using it in a turntable!

We can use them either in synchronous mode (capacitor or three-phase drive) or with their controllers using the integrated tachometer. Studer A80 capstan motors are also perfect, but I reserve mine as a spare for the A80's!

 

[analogsa]

I hear you analogsa, but I have a complete different sound experience

Fair enough. We cannot all like the same things. My comment was directed towards Spirit.


Btw, apart from an amazingly extended range of brushed DC motors Maxon also manufacture high quality BLDC motors. Some tt manufacturers use the latter which only adds to the confusion.

 

[analogsa]

perfect Studer A810 capstan motor.

What did you use for a pulley? The shaft itself?

 

[microstrip]

What did you use for a pulley? The shaft itself?

The shaft was around 9.2mm in diameter and I had a old bass pulley that I found in my drawers enlarged in a precision lathe to fit it just. The outer diameter was not critical as I could adjust the frequency of the drive signal.

 

[analogsa]

Sounds like an excellent solution.

 

[spiritofmusic]

Just spoken to the co-designer of my tt speed controller/motor/rim drive pod. He spent over a year toiling to get it right. Every time he introduced feedback loop methods to stabilise speed, culminating in experimenting with the Teres Verus motor, bass and timing suffered, and a grey colouration was imbued.

Burning the midnight oil culminated in the final design of outsize heavy platter for flywheel effect, high torque high revs small diameter (shirt button size) pinion rim drive wheel, and a classically simple control box using three regulators wired in series (three, to minimise ripple), and wire-wound multi-turn fine speed adjustment pot.

He compared his device to a pricey Paul Hynes triple regulator discrete PSU, but there was no discernable uptick in SQ.

My conclusion from all this is...if it ain't broke, don't fix it. Played some more vinyl with fantastic piano. Rock solid and stable, unwavering in the soundfield. I know piano is maybe the best test of speed stability, and the relaxed confidence of the sound suggests strongly to me that my tt is nailing things.

And the fact that a high quality commercial alternative provides no discernable improvement is swaying me strongly not to ruin things here.

I'm gonna invest in the SOTA RoadRunner speed tech system, to have a clearer readout of speed.

But a speed controller/motor/drive system that took so long to perfect, I'd be crazy to botch that.

Appreciate all the input on the thread.

 

[tima]

Just spoken to the co-designer of my tt speed controller/motor/rim drive pod. He spent over a year toiling to get it right. Every time he introduced feedback loop methods to stabilise speed, culminating in experimenting with the Teres Verus motor, bass and timing suffered, and a grey colouration was imbued.

But a speed controller/motor/drive system that took so long to perfect, I'd be crazy to botch that.

Perhaps the design is such that trying to retrofit a more accurate drive system is not feasible to the point of achieving what could be obtained if a more accurate drive system was incorporated from the start. I know you are highly invested in the Trans Fi Salvation and this may be an heretical question, but have you seriously considered an alternative?

 

[spiritofmusic]

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.

 

[morricab]

Marc. Imho you should download RPM app for your phone. Calibrate the app with your current strobe and measure the absolute speed stability and wow/flutter.

As everyone else as said, you need to establish a baseline to know where you are at.

Hi Bill,
I saw your comments on AA and saw that your speakers are now finished. Do you have an update with details here on WBF?
Cheers,
Brad

 

[microstrip]

Perhaps the design is such that trying to retrofit a more accurate drive system is not feasible to the point of achieving what could be obtained if a more accurate drive system was incorporated from the start. I know you are highly invested in the Trans Fi Salvation and this may be an heretical question, but have you seriously considered an alternative?

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 ...

 

[Phoenix Engineering]

The disadvantages of a DC motor are the brushes (mechanical and electrical noise) and the fact that they have a negative torque/speed slope (the bigger the torque load, the slower the speed). The latter can be compensated for by monitoring the current drawn by the motor (which is directly proportional to torque) and increasing the voltage to the motor as the torque (current) increases. This is a type of negative resistance and constant speed will be achieved when the negative resistance equals the winding resistance of the motor, so in effect, the motor does have feedback. The problem with this scheme is the resistance of the motor windings can change significantly with temp as copper has a positive temp coefficient. If the negative resistance of the supply is equal to the windings when cold, it will be under compensated as the motor warms up and the speed will droop under load. If the negative resistance of the supply is equal to the warm windings, so that speed will be stable when the table is warmed up, it will be over compensated when cold and the speed will increase with load and possibly become unstable.

If there is no current feedback in the supply, the speed will change with changes in stylus drag, and as the table warms, bearing oil viscosity and changes in the belt. Adding inertia in the platter is a positive step, but it only changes the rate at which the speed changes with load, it does not cure the problem, but it may move the variations in speed down below the audible threshold.

 

[spiritofmusic]

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.

 

[microstrip]

The disadvantages of a DC motor are the brushes (mechanical and electrical noise) and the fact that they have a negative torque/speed slope (the bigger the torque load, the slower the speed). (...)

IMHO some people prefer this type of motor just because of its sound signature. If people were really interested in a "perfect" motor they would use an intermediate air bearing flywheel like the Forsell - a great unit compromised by an inadequate low torque DC motor and its lousy controller. Its inertia moment is orders of magnitude better than anything I have seen in a motor : around 4kg 20 cm diameter platter spinning at 1000 RPM with an air bearing.

 

[Phoenix Engineering]

Agreed that inertia at the motor is also a step in the right direction. The early Papst motors used an external rotor that acted as a flywheel. They were also hysteresis type motors with no cogging and speed synchronized to the driving frequency so speed control was stable, precise and relatively easy to achieve. No brushes and no speed/torque slope.

David Karmeli uses this type of motor in the AS2000, which also has a significant flywheel on the motor. Difficult to beat this motor for performance, especially when driven properly.

 

[Lagonda]

Agreed that inertia at the motor is also a step in the right direction. The early Papst motors used an external rotor that acted as a flywheel. They were also hysteresis type motors with no cogging and speed synchronized to the driving frequency so speed control was stable, precise and relatively easy to achieve. No brushes and no speed/torque slope.

David Karmeli uses this type of motor in the AS2000, which also has a significant flywheel on the motor. Difficult to beat this motor for performance, especially when driven properly.

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/