Turntable power supply/motor’s role in SQ for belt drive TT

Just another reason to get a Sota. Better motor, better suspension, better bearing (magnetic thrust control), Better tonearm mount and you can throw the wall shelf away (which does not work in all cases.) 
The LP 12 has more "upgrades" than any other audio device on the planet. What a racket and LP12 people drink the Kool Aid. The LP 12's two basic problems are it's suspension design and cheap construction.
 

LOL, same old naysaying non Linn owning members are at it again I see! 

OP, ignore those folk and concentrate on your Linn upgrade.

I think IF funds allow, definitely go for the Radikal and the Karousel.
The Radikal is a excellent speed control and the DC motor is going to get you excited about your records again. The new Karousel ( I just fitted mine) is a superb upgrade...and if you do nothing else, this is a no-brainer. Not sure who told you AC motor is superior to DC motor, not the case with Radikal vs Lingo. Lingo 4 is good, Radikal is a LOT better, IME.

Soulines kubrick-jelco beats linn-itock. 

In two separate experiences, I have found that a motor controller, with or without a feedback mechanism, dramatically improved the performance of a belt-drive and an idler-drive turntable.  First was with a Nottingham Analog Hyperspace for which I bought a Walker Audio Precision Motor Controller, sort of with tongue in cheek, because I did not expect much if any difference.  Holy Cow, it was major.  The most significant improvement was in the ability to hear separate instrumental lines in the context of complex musical passages.  Next level improvement was bass definition. This sounds like audiophile BS even to me as I write it, but it's a true description of what I heard.  I then replaced the Walker with the Phoenix Engineering Eagle PS and Roadrunner tachometer, which does provide feedback to the Eagle.  That is even noticeably better, then on my Notts, and now on my Lenco idler-drive.  You're better off with an AC motor and a drive system.  The Phoenix stuff is now marketed by SOTA, as Bill Carlin just told you.  His stuff works.

You may want to look at the motor/controller offered by SOTA:
https://sotaturntables.com/product-category/eclipse-series/

@mijostyn - I’m happy for you that you like your SOTA and respect that you moved on from the 3 Linns that you previously owned. If you had done a proper wall mount you would not have had to tiptoe around your apartment. Can we get back to the task at hand though? I mean this thread is not about whether or not a Linn turntable is bettered by some other design - that’s why this hobby is so cool, there are lots of legit designs. 

I’m probably going to go with the Lingo 4 for cost reasons which is an AC design. I’m going to have to inquire or audition to determine bass sound quality/articulation between the Lingo 4 AC motor and the standard chassis Radikal with its more exotic DC motor. 

I owned three Linns. The SOTA is far superior. Is is not funny and I am dead serious. The Linn has so many weaknesses it can not be repaired. What do you think all these upgrades are about. It is just that back in the day it was the best table you could buy but look what it was up against. I kept going for supposedly better tables only to swear and return to the Linn and tip toeing around my apartment. By today's standards it is worse than a cheap Technics direct drive and everybody her knows how I dislike direct drive tables. I do find the Grand Prix Monaco very intriguing. I  love the aesthetic.  

Sell the Linn and buy a SOTA.

masi61

... is there some inherent electrical noise from the motor that makes it way into the analog signal thus producing an audible distortion through the cartridge/phono stage?

There shouldn't be if it's a decent turntable and is properly setup. That doesn't mean that motor vibrations couldn't find their way into the audio signal, but electrical noise from the motor shouldn't be an issue.

I’m also curious about why an AC motor would be less desirable than a DC motor (for a belt driven turntable. 

I don't think that a DC turntable motor has any inherent advantage over an AC motor at all and in fact, the opposite may be true.

My table has gone through a whole bunch of iterations as it has evolved to where it is now. https://systems.audiogon.com/systems/8367 This was not a case of simple upgrades from one table to another. This was modifying or upgrading one tiny little thing at a time. Motor power cord. Motor. Controller. Controller power supply. On and on. Dozens of things. Over more than 20 years.  

You can debate "why" certain things work all the rest of your life. If it turns you on go for it. If you need a story take your pick. In the end, "why" does not matter. What matters is does it sound better. If the motor, controller, and power supply are better, it will sound better. Whether it is worth it or not only you can decide, and you will know only after the fact. And that's the end of the story.

Hi,
drive, its all about drive. More pace, better and more stable image, better bass, less surface noise, etc.. AC ones need more complicated power supplies to keep noise down but have more inertia and torque, bass weight, speed is not affected by line voltage, have some cogging (if you have 3 phase motor and supply this is eliminated) and last forever.
DC ones still need a sophisticated supply for speed issues, are more quiet have a refined upper region, leaner bass, no cogging, but are affected by line voltage and do not last forever (brushless motors are better here).
Which is the winner, both have their own merits and depends on the TT’s construction and the quality of power supply. My understanding is that If a motor is mounted on the plinth a DC one would have more benefits, and if fitted externally an AC would be preferable. For me the stronger moter is best. Bear in mind that both motors can vibrate but in a different manner.