http://www.dagogo.com/View-Article.asp?hArticle=702
Very interesting. Taught me a thing or two I didn't know. Also, it's nice to see the author is DD friendly.
Kris.
Great article, Kris - thanks for sharing! :)
Marco.
chris@panteg
23-02-2010, 23:41
Yes thanks Kris ' that's an excellent article .
The article leaves out the fact that there are direct drive turntables with suspensions too like the Pioneer PL-600 I picked up for $25(£16) last week.
The mid seventies Techies had spring suspensions too, although they were stiffened up in the immediate predecessors to the current model.
We sold loads of the spring suspended SL1700, which you could buy very cheaply a couple of years ago. They're catching up fast with their "original new" price now though..
freefallrob
26-02-2010, 14:36
Thanks for that, interesting real world read. I've owned both BD and DD types in various guises and can appreciate the + & -'s of them both.
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 (most turntables introduce noise either from the bearing or the motor, or both). 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 (this can be true but is by no means inherent to this type of turntable - a lot depends on how high the suspended mass is and how great the torque of the motor is - coupled to the tension of the drive belt and how compliant it is). 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 (no, the belt is there to prevent short circuit of the sprung suspension, to isolate the suspended platter and arm from external noise and motor noise. The mass of the platter is intended to overcome motor cogging artifacts). If you recall the little playground animals that sit on re-purposed automobile coil springs, you might understand a basic design flaw (except, other than using a mass on a spring, this is not a close analogy to a three point suspended turntable. First, turntables use conical springs which impart a self centring element; second, three springs are used which are referenced to a single plane - the chassis. The centre of gravity of the suspended mass lies within the circumference of the three springs. On the child's ride, the analogy relies on, the supported mass is purposefully outside the COG of the spring and so it is inherently unstable.) 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 (this is not true and anybody can see that a spring suspension that uses three conical springs is self centring in a manner that is inherently outside the abilities of the child's ride refereed to). 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 (on the contrary, the turntable positions the mass in a very similar manner to that used by an automobile).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 (this is due to the mass of the suspended element, the horizontal compliance of the suspension coupled to the belt tension, compliance and motor torque). 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 (SOTA were not the first to do this by any means). Because they hang the sub-chassis from four springs, it always wants to return to equilibrium when put into motion (no more than a conical spring does - indeed, the oscillating problem commented on earlier was a facet of early SOTA designs precisely because of the low horizontal compliance of the suspension and the high suspended mass which meant that once destabilised it was reluctant to stop moving). 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 (again, this is far from unique and not a SOTA first - in fact, I would say that it is essential for a suspended turntable) 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 (the idea of using the platter as a flywheel was introduced many, many years before the SOTA and was in common use by the time they produced any turntables - pretty much all suspended designs used this principle (Pink Triangle excepted). I owned a Sapphire for a long time. It made good on the promise of speed stability and isolation from outside noise (it isolated well from external noise because it had a high suspended mass and a very compliant suspension - not because of the inherent geometry of that suspension).
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 entirely depends of the level and frequency of the acoustic feedback. It also depends on precisely how, and on what, the turntable is supported). This version of belt-drive usually has the best speed stability, while effectively isolating the motor from the platter (the motor is more directly coupled than in a well engineered suspended design. However, because the spatial relationship of the motor and platter is fixed there is the possibility that speed stability will be enhanced - this is by no means a given though).
The problems with direct-drive are not so much inherent in their design (I would argue that at least one of the major problems is inherent to the design - though that does not mean it cannot be overcome), 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 (this is an oversimplification. If a feedback loop is used then a logic must be applied. Most servo systems require the mass that is to be influenced to be low or the correction element is delayed by the need to overcome inertia. If the servo is infinitely powerful and the influenced mass is infinitely low, then the correction will be simultaneous. In reality, neither of these situations exist. In addition, there is the danger that correction effectively creates steps in speed stability. The option exists to both apply varied logic to the manner in which information is processed and the manner in which correction is applied. Rather than monitoring the speed every revolution one may choose to monitor it every two revolutions or ten etc. One may also choose to apply correction in a gradual sense etc. There is also a problem with actually collecting the rotational data. Traditionally, feedback loops rely on collecting as much data as possible. The problem with a turntable is that it rotates very slowly). 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 aluminium casting which will ring like a bell (it's not so much that it will ring like a bell but the fact that the motor noise is effectively coupled directly to the record and hence the cartridge). The lack of mass in the platter allows the motor and speed regulation to overshoot/undershoot the speed (in fact, it is often the mass of the platter that causes this, not the lack of mass). The drag of a stylus slows the platter down, which the turntable "sees", and tries to correct. Unfortunately, it overshoots the speed (over-compensates) (by the time the servo has overcome the inertia of the platter to achieve the desired correction it has imparted kinetic energy that causes the overshoot), 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 (this can be the case but the problem is more complex).
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.
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 (this is very unlikely to be true in the real world unless the turntable is on an exceedingly low friction mount and the platter goes through significant acceleration and deceleration). All these gyrations create noise (no, they do not create noise, they create instability which is not the same thing at all) , 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 (how a material damps another is very dependant on the impedance match between the item being damped and the damping element. Also, the specific level and frequency of the signal one is seeking to attenuate. My experience is that large, heavy wooden plinths are rarely the best solution). 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’s vinylphile readers, I hope this is of some help, though it wouldn't surprise me if it only causes "paralysis from analysis".
I should add that there are significant issues with suspended turntables but they are not highlighted in the above article.
Very informative comments, thank you Mark.
Kris :cool:
Many thanks Kris.
The point of my comments (in red) are that it is dangerous to extrapolate the contribution of specific elements from the behaviour of a complete system.
I also think it is interesting that the author chooses to use the SOTA as an example. Unfortunately, they attribute a number of qualities that are not unique (as they imply) or not directly related to the performance aspect to which he links them. When the first SOTA was introduced the use of springs in extension, or a flywheel platter, were in no way unique. What was more unusual was the use of four springs and the relatively high mass of the chassis. The chassis was balanced (to compensate for different arm weights) by adjusting a quantity of lead shot at each corner of the chassis (a large rectangular MDF plate I seem to remember).
The chassis instability ('shimmy') that the author refers to has little to do with the movement of the arm on an eccentric record and more to do with the machining of the platter and whether it is properly balanced or not.
For me, the most interesting DD solution is the one that Brinkmann have introduced. In this system the DD motor is low torque and the platter has a significant mass to behave as a flywheel.
pure sound
01-03-2010, 11:12
Goldmund did something similar 30 years ago with its lead loaded acrylic platter and the Papst EDS1000 mechanism. That was suspended too.
Did they, I didn't realise; I'm not a fan of those multi-laminate platters though.
pure sound
01-03-2010, 22:11
It wasn't a multi laminate platter as such, just an inch or so of black acrylic with about 10 or 12 lead cylinders (about 30mm diameter) inserted underneath around the periphery.
That was (still is) is a very good deck, possibly the best Goldmund made.
Hypnotoad
02-03-2010, 16:32
The mid seventies Techies had spring suspensions too, although they were stiffened up in the immediate predecessors to the current model.
We sold loads of the spring suspended SL1700, which you could buy very cheaply a couple of years ago. They're catching up fast with their "original new" price now though..
I have one in storage at the moment, I often pondered putting a better arm on it, it seems to have the same cutout as the SL1200 Mk 2.
The mid seventies Techies had spring suspensions too, although they were stiffened up in the immediate predecessors to the current model.
We sold loads of the spring suspended SL1700, which you could buy very cheaply a couple of years ago. They're catching up fast with their "original new" price now though..
Some of the Pioneer models are still inexpensive used. I picked it up to sit next to my chair in the living room to get through this season of 'American Idol' and the rest of my wife's shows.
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