Direct Drive vs. Idler Drive vs. Belt drive

@atmasphere ,

"Given how innovative AR was at the time, its a bit surprising that they chose to under-serve their concepts as presented in this machine. If they had been a bit more aggressive and upscaled it a bit, they would have built a classic."



If only indeed. Nevertheless, the AR turntable was certainly no slouch when it came to performance.

I’m guessing that AR didn’t believe there was a market for a more expensive model, given that the AR turntable was all about outstanding value for money. In fact it would take decades before it could be beaten on that score.

As for technical improvements, well you know the history. The Thorens TD150, the Ariston RD11 and the Linn LP12 all later tried to improve on the cleverness of the initial design to various degrees of success.

On of these days Linn might even admit it, but don’t hold your breath.

Now if only AR had taken out a patent..

Anyway here’s a great YouTube video by M. Zillch to enjoy.

Audiophile Turntable 101: Acoustic Research AR-XA TESTED

https://youtu.be/1rgK0YMsJXM

I’m guessing that AR didn’t believe there was a market for a more expensive model, given that the AR turntable was all about outstanding value for money. In fact it would take decades before it could be beaten on that score.

I not sure I agree with this... budget turntables have always been problematic. Empire was making better machines back in 1961, but they might have cost a little more. Its certainly telling that an Empire goes for more money now than an AR.  I think the issue comes down to cost and that AR sort of 'got away with it' when they used a clock motor to run the turntable. Allied used to sell the AR; I had to deal with headshells with stripped cartridge mounting threads, stripped threads for mounting it to the arm tube, warped headshells, perished platter pads (the foam was terrible but the turntable couldn't support anything better); it was annoying that the overhang couldn't be set and the bearings in the arm were pretty cheesy. The platter bearing seemed alright though. If you really want to look at a budget machine that was better at ticking the boxes, perhaps the old Connoisseur BD2 would be a better choice. They didn't have any better bearings, but because they were at a 45 degree angle, the chatter was a bit more bearable if you'll pardon the expression.

This is something I posted in wbf to a gentleman that was against servos in DD TT because he said that he can hear the damage that servos makes to what he listening through a DD turntables ( as the Technics SP10MK3 or Denon DP100 and the like. ) . Could be interesting to think a little about:

""" But things are " critical " for say the least about your " entitled " against servos because the recording LP cutting machines uses DD non-coreless motors as the Technics Sp-02 on the Neumann or the servo controled ( as the Sp-02 ) Parker motor in the Lyrec lathes. In Scully lathes some gentlemans used the MK3 Technics motor. Altivar was other used motor and obviously its own Neumann one and even Denon.

Raul, you miss the obvious.

The Technics SP02 lathe motor was specficially designed to drive the Neumann lathe with the 70lb Neumann flywheel attached.

If you have a low mass platter with direct drive, the speed correction becomes more invasive. With a high mass platter, the inertia and resistance to stylus drag is much higher, and speed correction less invasive.

Furthermore, DC motors have zero torque at constant speed. Torque is only generated when speed change is occurring in a DC motor. Therefore DC driven direct drive turntables are just like digital - only a little bit out all of the time. In your typical lightweight platter/DC DD motor, it is most likely the platter is seldom at the correct speed at a micro level.

Furthermore speed correction with a DC motor can be scoped - it is a saw tooth trapezoidal recovery ( rough in plain language )  compared to an AC motor recovery which is sinusoidal when scoped ( much smoother and more consonant with music ).

By the way, most of the vintage lathes are worm drive.

Dear @Dover : Agree but that does not means dissapears, only " less invasive ". problem is that we can’t know what that means exactly.

In the other side gentlemans ( other than ML. ) that own the Technics MK3 did not posted about " problem " with the servo. I owned the MK2 and never detect it against BD TT neither with my Denon’s and if I rememeber Halcro neither in that specific issue or even lew.

What I said is that what we can detect in a DD vs BD/ID TTs couldbe a " trouble " with other kind of DD designs characteristics and not because the servo.

R.

By the way, most of the vintage lathes are worm drive.

Furthermore, DC motors have zero torque at constant speed.

@dover  These two statements are false. I own a Scully lathe which is typical of what was used to make many older recordings. Its not worm drive. It employs a 1/8th horsepower syncronous motor which drives an anti-vibration coupling which then drives a transmission (which allows for shifting from 33 to 45 rpm). The transmission employs bevel gears in an oil bath but no worm drive. Its output is a shaft which drives another vibration isolation coupling; that in turn drives the platter directly, which rests on a set of carefully machined bearings (which require frequent attention).


DC motors have torque even at constant speed, so long as there is a load. This link might be helpful:

https://www.motioncontroltips.com/torque-equation/
However its a bit of a misnomer to equate a servo controlled multi-pole motor with a simple DC motor, and its also worthy of note that AC motors have a similar property of lockup being the point of highest torque output (as I'm sure you know quite well). I'm guessing that what might have been conflated/misconstrued in your comment above is the fact that when a motor has no load, its **current draw** is its lowest. But I think you'll find that how much torque it has is another matter altogether! Certainly a motor at constant speed will be making torque...
Its one thing to 'scope the waveform that is driving the servo operation, its quite another to see how the system responds to that waveform. I very much doubt that the platter speed variation can be represented by a triangle wave!