Way cool! Did not know about the Dual. Perhaps I should have gone to R�MAF after all to hunt down each of the modern DD's that we know so little about.
I take it you were dissatisfied with your Mk2 on other grounds besides "bass dynamics and tightness", One big diff between my Mk2 and Mk3 is that I made a better more sophisticated plinth for the Mk3. The Mk2 was all slate. The Mk3 plinth is equal parts slate and cherry wood and weighs around 90 lbs. I found that the addition of the stiff hardwood dampens the slate, whereas the slate is very good for channeling energy away from the Mk3 chassis. Anyway, the Mk3 plinth is very neutral. The Mk3 itself imparts a little more energy than the Mk2 and has very low coloration, if any. However, I thought the Mk2 in slate was very fine and could have lived with it. I firmly believe there is such a thing as "good enough". After good enough, the rest is a hobby. |
The closest to the Dual 701 motor design is the later version of the Kenwood L07D motor because, like the Dual, it has two layers of coils except Kenwood made them in star shape to avoid patent infringement. Compare to the older version I think I would prefer the later one because the magnetic field is symmetrical, hence, I assume, more balanced rotation. If people who own both of them, I would like to hear about the sonic difference. Which version do you have, Lewm? Lewm: "I firmly believe there is such a thing as "good enough". After good enough, the rest is a hobby." Great quote! _______ |
Far as I know, the motor with the symmetrically arranged coils is indicative of a second generation L07D. There are photos of such a tt on the LO7D website hosted by Howard Stern, who serviced both of my L07Ds. But in real life, I have never seen a second generation LO7D for sale or known one to be in the hands of an end-user. (It differs from the first generation type in other ways besides the motor structure; the tonearm rest and the adjustable support feet were also built differently, and there may be some differences in the electronics, or not.) I suppose if you canvas the LO7D email group, you might find one. Last year there might have been one for sale on the Hifido website. Which is a long-winded way of saying that my L07D(s) (both of them) are the much more common first generation type with the assymetrical coils. There has to be a reason why Kenwood chose to build it that way, but I cannot imagine it. Do you think it was to avoid infringing on Dual's patent? Note that the Bardo coils are not symmetrically placed around the spindle, either. |
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. :) ______ |
Hiho, His second post was in response to something I must have written, since he is addressing me. Yet I have no recollection of ever reading this treatise before. Also, he talks about "poles" in coreless motors, so this means I am full of baloney (to put it nicely) when I said that the Teres (was it?) motor cannot be coreless if it has "12 poles". I have to do more reading on this subject because obviously I am not qualified to have any opinion. Now, where can I buy a Dual 5000CS? That would be a great motor for my Lenco. |
