Publisher Profile

Audiophile Q&A: Turntable, Direct-drive versus Belt-drive

(or, it just depends...)

By: |

Editor’s Note: Audiophile Q&A is a new column on system related topics. Readers are invited to suggest topics to the Dagogo Staff, and we will do our best in addressing them. Opinion expressed by Dagogo reviewers is their own, and does not represent Dagogo’s position. Our inaugural article is on turntable, authored by Phillip Holmes.

There are a lot of opinions on which type of drive system is best. There are certain inherent strengths and weaknesses in all the drive schemes. I’ve heard good examples of all versions (idler wheel, direct drive, belt drive). There are subtypes to consider as well.
When properly adjusted and maintained, there are many, many, turntables that can get the job done: spinning a record, at a consistent speed, without introducing noise. Some designs are more stable than others, some require an extraordinary amount of diligence when it comes to set-up and maintenance (something I like to avoid).

Several things to point out are:

Belt-drives tend to modulate a spring-suspended sub-chassis. It’s something I noticed with several tables I’ve used. I’m speaking specifically of players where a sub-chassis sits on top of three cone-shaped springs that are compressed by the weight of the platter/bearing/sub-chassis. The springs are there to isolate the sub-chassis from acoustic feedback. The belt is meant to isolate the platter from the cogging of the AC synchronous motor. If you recall the little playground animals that sit on re-purposed automobile coil springs, you might understand a basic design flaw. Just as the child will oscillate to-and-fro on the spring, the coil spring suspension in a turntable has the tendency to be unstable. As soon as the child gets on the animal, it starts to roll and deflect to the side. Unlike an automobile that puts the spring in the middle of a suspension which limits the possible motion of the spring, the playground animal (and turntable) is unstable. My first vinyl rig was a rebuilt and modified AR-XA. It had a dinky little AC synchronous motor driving a sub-platter with a rather loose belt. If the record was pressed off-center, which is very common, the back-and-forth movement of the cartridge caused a modulation in the sub-chassis. There were different tweaks to be tried, but the design was always unstable. There are many similar tables, some better than others.

A better solution was SOTA’s introduction of something that seems rather obvious: hanging/dangling the sub-chassis from the springs. Because they hang the sub-chassis from four springs, it always wants to return to equilibrium when put into motion. The weight of the sub-chassis is pulled straight down by gravity, so there is only one position where it will be stable, and it will always return to that position. Think of it like a pendulum. Once the pendulum stops moving, it will be “pointing” down to the center of the planet, the source of gravity. If the pendulum were somehow perfectly balanced and pointing up, it would take only the slightest input of energy to throw it out of balance and cause it to fall, where it would eventually stabilize pointing straight down. SOTA also used a more sophisticated motor, motor-drive electronics, and cast-rubber belt driving the periphery of the platter. The platter’s mass was concentrated at the outside edge, giving it better “flywheel effect”. The result was better speed stability than previous belt-drive systems. I owned a Sapphire for a long time. It made good on the promise of speed stability and isolation from outside noise.

Illustrations courtesy of SOTA Turntables
In the case where a belt drives an unsuspended platter (The Well Tempered table, the classic Empire table, etc..), the motor is isolated by the belt. The motor is sometimes in its own enclosure, physically separate from the plinth. Mass and/or careful placement is used to prevent audible feedback into the plinth holding the bearing and platter, which is usually isolated by compliant rubber feet, or placed on an isolation platform. A common problem is bad motors. I didn’t like the motor in the Well Tempered Record Player (this from nearly 20 years ago), and I despise the Pabst motors from the ’70s. Both were noisy and had poor speed regulation. The noise could be transmitted through the belt, even though this was the reason for the belt. The best of these designs are incredibly good. Because there are no springs involved, an off-center pressing won’t cause problems. Most acoustic feedback is quickly damped and winds up being well below the signal, thus inaudible. This version of belt-drive usually has the best speed stability, while effectively isolating the motor from the platter.
The problems with direct-drive are not so much inherent in their design, but with their build-quality/execution/use/setup. The first problem, the one which garnered direct-drives their negative press, is the combination of a powerful motor, light platter and sketchy motor control. Cogging, ringing and a constant overshooting of the speed regulation is the result. The motor, much like a typical AC synchronous motor, is not perfectly smooth. The noise from the motor is coupled to what is usually a thin aluminum casting which will ring like a bell. The lack of mass in the platter allows the motor and speed regulation to overshoot/undershoot the speed. The drag of a stylus slows the platter down, which the turntable “sees”, and tries to correct. Unfortunately, it overshoots the speed (over-compensates), and is too fast. This goes back and forth all record long. An electrical engineer told me this was excess “servo gain”. I don’t know if that’s the case, but it makes sense to me.

The second problem with direct drives is that all those electronics and the powerful motor release EMI/RFI, which is only inches from a cartridge. The noise rides on the signal and may or may-not be audible, but definitely wastes headroom/power and reduces resolution. The aluminum platters of the Technics and Denon direct-drives provide very little shielding from this noise.

Illustration courtesy of Musical Surroundings
The third problem with direct-drives is that most (there are exceptions) come with ridiculously inadequate plinths. With a table like the Technics SP10 Mk III, the motor is massive and powerful. The motor creates an equal/opposite twisting of the turntable chassis, causing a feedback loop where the motor and chassis continue to react to each other. All these gyrations create noise, which is transmitted through the plinth to the arm, and through the platter to the cartridge.

The fourth problem is that most direct-drives in use today are getting rather old. Their electrolytic capacitors are drifting from nominal, creating problems for the servos, oscillators and the like. Finally, one fails and the ‘table is rendered a boat-anchor.

The solution for these problems requires an investment in time and money. First, to make sure the electronics are functioning accurately, the electrolytic capacitors should be replaced with new ones of the exact same specification. You can add extra capacitance in the power supply to filter out spurious noise that might make its way into the control circuitry, but changing a coupling cap in the control circuitry to a totally different value might make the turntable unstable or render it a non-turntable.

Second, if there is speed drift with no record being played, there could be a servo or voltage regulator that needs adjustment. All the popular direct-drive turntables have service manuals that any competent technician can use to tune up the electronics.

Third, there are materials available that will shield the cartridge from the noise of the electronics. Cloths, foils and metals can be fashioned into record mats to sandwich between the regular mat and the surface of the platter. Also, some of the noisy electronics can be moved externally, specifically the power supply transformer and rectifiers. This was done with a few mass-produced direct-drives like the SP10 mk2 and mk3. One of the reasons they are good is that the noisiest part of the electronics has been situated well away from the playing surface of the record in the form of a detached power supply.

Fourth, it is important that a massive plinth is employed that will act as a sink for the vibration. The most successful of these that I’ve heard are made of wood. The rather soft, compliant, nature of wood allows the chassis of the table to effectively couple to the plinth, and to transmit and damp spurious vibration. In the case of the Technics mentioned above, the stock obsidian base was very massive, but it was difficult to produce two perfectly smooth and flat mating surfaces so that the table and plinth effectively became one massive unit. Even if such precision was available, it would never have been used in a consumer audio product. Certain parts of the chassis will resonate/vibrate against the hard surface, while other parts are mechanically grounded. The result is ringing and movement of the chassis and all the pieces it holds. It’s not dramatic, but does explain why many people who originally heard the Technics thought the SP10, with its stock plinth, was “bright” or “edgy”.

To a large extent, the problems with direct drives are similar to the problems with idler wheel turntables. Done right, a Garrard can be great. If not restored and mated to a good plinth, it resembles a washing-machine motor directly coupled to a ringing hunk of metal.

That’s the long answer to the question.
The short answer is that it depends on what kind of listening you do, how much you need isolation from feedback, and how much you are willing to spend. A budget belt-drive using a rigid plinth can be much better than a budget direct-drive. A cost-no-object building of a Technics SP10 mk3 can literally beat the competition like a cheap rug. But to get to that point requires that you purchase an expensive and long-out-of-production turntable, make sure that it runs perfectly, build a heavy/expensive plinth, and do all the other things that is required for a successful direct-drive platform.

The final point is that none of these methods for turning a record are way better than any other method. Like getting the most of a F1 race car, fine-tuning a turntable requires a lot of due diligence.

To Dagogo‚Äôs vinylphile readers, I hope this is of some help, though it wouldn’t surprise me if it only causes “paralysis from analysis”.

  • (Page 1 of 1)

Leave a Reply

Your email address will not be published. Required fields are marked *

Popups Powered By : XYZScripts.com