I believe the Brinkmann Bardo and Oasis use the gentler servo speed control. Here's what they wrote in their white-paper; it's a little long but it's a good read:
PROBLEM WITH DIRECT-DRIVE
Studios (radio stations in particular) demand quick start-up times turntables typically have to reach their correct speed within half a revolution. For LPs this means 0-33 1/3 rpm within 0.9 seconds. Such acceleration figures can only be achieved through use of high-torque motors and correspondingly tight coupling between the drive and platter. It isnt a surprise then that for decades idler wheel drive designs were the defacto standard in studio applications. But idler wheel turntables also had seriously high maintenance costs in order to be up and running 24/7 and to avoid rumble and other sound degrading issues caused by worn out idler wheels to affect the sound negatively. Thus out of necessity, in the late 1960s manufacturers of studio turntables began to look for low(er) cost maintenance alternatives. They came up with direct drive, whereby the platter was placed directly on the motors shaft, ie the stator was mounted around the bushing and the shaft was used as the rotor and voila, the goal was achieved; at least in theory.
But start-up times of less than 1 second necessitated high torque motors, which designers achieved by using motors with 32 and more poles. The penalty they paid were heavy cogging effects accompanied by high wow & flutter numbers. The cure was found in quartz locked motors and phase locked regulators; which corrected for any deviations from their preset with an iron fist. On paper at least, these corrected direct drive turntables boasted hitherto unimaginable low wow & flutter numbers down to 0.001%. But the rigorous iron fist regulation prevented the platter from spinning smoothly; instead, the regulation caused the platter to oscillate continuously between speeding up and slowing down. These start/stop motions translated into an unpleasantly rough and hard sound; odd as wow & flutter numbers in the 0.001% range are deemed inaudible.
Once the direct drive technology had gained a foothold in pro audio applications, the benefits of mass production (ie. trickle down effect) made sure that very soon even $100 turntables were equipped with direct drive and advertised as having less than 0.01% wow & flutter. This is precisely where direct drive got its bad rap sheet. Under closer scrutiny however, this assumption were based on some misunderstandings. For one, in home audio application use, turntables are not really required to reach 33 1/3 rpm in less than a second, thus 32 pole motors and phase locked regulators are not really necessary either.
THE BRINKMANN SOLUTION
Having decided to utilize a direct-drive mechanism for our new turntable, we began searching for the appropriate motor. Sadly (or luckily, as it should later prove) and despite much effort we were unable to find a motor that was up to our stringent quality requirements. We therefore decided to design and build the motor in-housewhich had the nice side effect that we did not have to cut any corners and instead were in the fortunate position of defining all relevant parameters ourselves. The motors stator consists of four specially designed field coils, which are mounted concentrically with high precision around the platter bearing. Based on listening and tuning sessions, we decided to forgo the typical 90-degree mounting angle in favour of a non-standard 22.5-degree raster, which, due to the magnetic fields overlapping, further reduced cogging. The motors rotor also acts as the sub-platter and carries a magnetic ring with 8 poles on its underside.
The drive mechanism, based around Hall sensors and an encoder disk, is designed in such a way that there is just enough power to bring the 10 kg heavy platter up to 33rpm in about 12 seconds. Conversely, only a minimal amount of energy is actually necessary to keep the rotational speed at a constant. While the drive mechanism is indeed direct, power
is actually transferred without any contact. This soft coupling via a low power magnetic field translates into a silent drive, which reduces cogging further. One of the main attributes behind the sound quality of the Oasis has to do with our proprietary motor control. It works proportionally, i.e. it transfers just enough energy to the motor for it to remain at constant speed. Conversely, due to our ultra low-friction bearing, only a small amount of energy is actually necessary to keep the motor at constant speed. Previously available regulators typically work disproportional and rather abruptly: they speed up and slow down the motor very rapidly when necessary.
During the development phase of the Oasis turntable, we spent many long hours auditioning several different regulator designs; it became quite evident that utilizing our concept of proportional regulation always resulted in better sound: typical harder motor control concepts produced a sound significantly lower in quality, with less color and drive.
I suspect their decision "to forgo the typical 90-degree mounting angle in favor of a non-standard 22.5-degree raster" is influenced by Dual's design of the EDS-1000 motor, which also has the same coil arrangement...
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