The topic about the Dual motor and later generation of coreless motors in L07D and Bardo has been covered by an Audiogon member who is also an aerospace engineer, Wjsamx in a thread about the Brinkmann Bardo from last year, as you might remember reading it.
Here's what he had to say:
06-15-10: Wjsamx
Dual came out with the first and only EDS (electro-dynamic suspension) DD TT motor, for which they've never gotten any credit. Being an aerospace engineer, I can tell you this type is the only true magnetic direct drive motor. The Technics platter is nothing more than a magnet that sits in a rotor, is configured horizontally, which essentially becomes a standard motor stabilized by tach signals and OCD type electronics. The Technics motor suffers from pole jerking, magnetic drag, hysteresis, and requires a very large amount of power. The Dual EDS motor works like a modern magnetic railway. When the magnet is between 2 poles, the powers of the 2 poles are proportionate. In other words, if the magnet is dead center between the 2 poles, both poles will have 50% power, but if 80% of the magnet is over one pole and 20% of the other, the power is split 80/20 and so on in a linear fashion. It only requires 50 milliwatts of power to operate, since opposing magnets are the major force behind its propulsion. There is no need for quartz control. The hall sensors monitor the strength of the magnetic field within the system and hold stable regardless of fluctuating line voltage. A heavy platter is not required, and the technology of EDS actually allows the platter to (microscopically) levitate when it is operating, significantly reducing typical negative spindle and bearing contributions. This motor is dead silent. Unfortunately this EDS motor never received recognition and was very expensive for Dual to manufacture. At one time, Dual had 3000+ employees and completely made 100% of their own parts and motors in-house. To compete and save money, they "cheapened" newer motors and went along with the crowd of quartz control. BTW, the motor in the Dual CS5000 is an EDS type motor, although it provided belt drive. It seems that the Brinkmann DD motor is nothing more than a new type of Technics DD motor. The fact that the coils are not totally equidistant means it's "pushing" and "braking" in an un-uniform manner favoring one side. I believe they bandaid and hide issues by the use of a heavy platter. I'm in no way discrediting other manufacturer’s contributions to DD TT technology. Technics may have been the first to the commercial market with DD, but Thorens developed and patented the first DD motor way back in 1929. With respect to the discussion of "magnetic direct drive", Dual was the pioneer and implementer of this type of DD motor. Technics and other manufacturers have nothing to do with this type of motor as their DD motors act more like stepper motors. So the correct timeline is Thorens invented the first DD motor, Technics was the first to market the DD TT, and Dual was the first, last, and only to invent and market the EDS magnetic DD motor for use in turntables.
06-16-10: Wjsamx
Dear Lewm, There are 2 different motor designs for the K07D. The initial Kenwood motor that looks similar to the Brinkmann (and the Dual) but with 6 red coils was a patent infringement on the earlier Dual design. This is why Kenwood had to later change the design to the green star shaped coils, which you can see are not asymmetrical. Kenwood and other Japanese manufacturers thought they could get around the patent issue by using a different number of coils, placing them asymmetrical, compensating with electronics, and changing the specs. It was very common practice, and still is today, for manufacturers to purchase competitors products, completely disassemble them, study the design, and attempt to deviate enough in their own design to try and beat any patents. The Dual EDS motor had 8 double field coils in symmetry with a special conductor plate below it. The magnet was made of barium ferrite and had 8 pole symmetrical magnetization. The electronics in this system were so minimal compared to others that it fit on a round circuit board the same diameter as the bottom of the motor (5 inches). The motor was one complete assembly including the electronics. The platter just fit on top of it. In regards to the Brinkmann motor, I can't understand the reason for the odd placement of the coils. One would think there is a dead spot of power in its rotation which is why I believe its concept is to push and brake. The motor seems by design to only pulse power to the rotation as needed. Once the heavy platter is at speed, the energy within its mass is creating the needed centrifugal force for rotation. The tach feedback will sense speed deviation and only micro-pulse the "motor" as necessary to keep the platter steady at speed, like cruise control. Judging by the size of the motor, it's not meant to "direct drive", it is just too small and weak. It's really a "soft drive" system. Weak micro-pulses of "magnetic" power to the platter would certainly not create a large impact on such a heavy platter, thus eliminating any cogging effect. I do like it's simplicity, and it must obviously work, although they don't advertise any specific specs other than it takes 12 seconds for the platter to reach speed. The white pages on the Brinkmann motor suggest they are using a non-standard 22.5 degree angle on the coils with an 8 pole magnet, claiming that the overlapping magnetic fields reduce cogging. Isn't it strange that this Brinkman motor is very similar to the Dual EDS motor, which has 8 coils instead of 4, both use the coils at a 22.5 degree angle, both have hall sensors, and both have 8 pole magnets. I guess the Dual EDS motor patent has long expired. Essentially, one can get a Dual EDS motor, drop it in a plith, and have a Brinkmann for about $200 + tonearm. It might be ugly, but it won't cost 8 grand. Honestly, and with sarcasm aside, if I were looking for a new TT, I'd consider the Bardo, but only after having a demo.
Have a look at Dual EDS motor:
Exploding view of motor - - - & - - - Cutaway view of motor
Brinkmann white pages:
Brinkmann whitepaper in PDF file
A lot to absorb but fascinating stuff to read about motors. :)
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