Eminent Technology ET-2 Tonearm Owners
There is a sound engineering reason to put any mag dampening to be at the wand end of the spindle. Since the mag tends to resist spindle movement, it acts as a pivot for any non axial spindle motion Since the cartridge is at the end of the wand and not at the end of the spindle, there is a force moment induced by stylus movement. The spindle can, at frequencies below the air bearing resonance point, move about this pivot point in a non axial manner. Having this pivot point at the wand end causes less teter totter due to spindle sleeve clearance than would be the case if the pivot point was at the counterweight end. This benefit is clearly audible. Exactly the same design feature is present in TT's with inverted main bearings. Of course the mag is closer to the signal wires. The choice is yours. |
Thanks Dover, Ketchup and Richard for addressing my concerns. Well, I must admit I was somewhat skeptical about magnetic damping, but I am now convinced of the benefits. Some preliminary observations: So far, I have used a single refrigerator magnet that conveniently detached itself from the back of a cooking timer. I glued this inch-squared flat magnet to a small block of glued layers of cork about the same size as the magnet. I situated it on the wand side of then arm pillar; frankly, only because I still have the damping trough attached to the pillar (with paddle disengaged). I plan on trying it on the other side, as well as trying other, more powerful magnets. The magnet is as close as possible to the spindle without touching it. I listened to the same musical selections several times, with and without the magnet. The results are relatively subtle but unmistakable. There is a general "cleansing" of the sonic picture; as if a fine mist is removed. Bass definition is improved with an increase in one's ability to hear pitches in the bass; as opposed to simply low frequency energy. The highs gain a bit of refinement and sound slightly less ragged. On "The New Breed" from Donald Fagen's new release Sunken Condos, Walt Weiskopf plays both alto and tenor saxophones. Without the magnet, it is very difficult to hear when he plays alto vs tenor. With the magnet, more of each horn's individual character can be heard. Also, for an LP with otherwise very good sound, the bass, while being powerful and very well extended, has a strange "drummy" quality with less than good definition. The magnetic dampening brings a welcomed slight improvement in pitch definition. Curiously, the soundstage seems slightly smaller with the magnet; perhaps a result of the increase in control and definition. The differences are not earth-shaking by any means, but definitely worthwhile. I have not experienced increased volume; perhaps with the more powerful magnets. Biggest surprise of all: record surface noise seems reduced. LP surfaces are quieter, and the loudest clicks and pops sound less obtrusive with a more subdued character. More to follow. |
Richardkrebs - I'm a little disappointed you dont think outside the box, or in this case arm. What about running 2 ET bearings in a T bar configuration, armtube in the middle. You like magnetic dampening but worry about the eddy current. Try standing on your head and thinking upside down. You dont have to use the bearing tube. Why not use a magnet as a counterweight and an aluminium bar mounted on the plinth. Why not go the whole hog and put an accelerometer on the bearing housing, that way you can measure the resonance and employ electromagnetic dampening driven from a feedback loop and active servos to dial out the exact resonance. What I do know is that added mass will have altered the dynamic stiffness of the bearing and the fundamental resonance. It will increase the instability in that air bearing. You are running 12psi - this is on the lower end of what most are running ET's. With the added mass you are increasing the very instability you are complaining about with the magnets. Have you measured the dynamic stiffness and fundamental resonance after adding mass ? Have you calculated how much you need to increase the pressure by to provide the same level of rigidity in the bearing as the standard arm ? Have you measured the impact in the high frequencies of being able to achieve the same level of rigidity with less mass ? When it comes to resonance mass is your enemy. Do you put lead in your gumboots for a smoother ride when you go tramping ? Perhaps you should resign yourself and go to a unipivot. An air bearing will never be as rigid as a unipivot - you are losing so much of the leading edge of notes. That would solve all your anxieties and give you a whole new set of issues to fret upon. PS The tantric yoga is no joke - stand on one leg, put the other to your ear, and you may hear a little more bottom end. |
Dover Well I have to say am very impressed with your flexibility Dover. I am very happy that I run every day for my health. But I can’t even touch my toes. I guess I should start Yoga..with my wife. Frogman – your observations are similar to mine and the reason I am still using the magnetic damping. Here is how I am currently set up. ET 2.5 Magnetic damping What is not obvious in the pic is that there is actually over one inch of clearance between surface and spindle when it comes across. Can the positioning be improved ? Will try three on top of one another. I just placed three for even distribution as the spindle comes across. I am assuming placing any magnets directly under the manifold will have a reduced effect ? I could try this with the ET 2.0. Home depot has a large selection of various magnets. http://www.homedepot.com/webapp/catalog/servlet/Search?storeId=10051&langId=-1&catalogId=10053&keyword=magnets&Ns=None&Ntpr=1&Ntpc=1&selectedCatgry=Search+All My wire exists at the armtube. After getting the Dynavector gauss level info about using thousands of gauss in their tonearm – these 50 (approximate) gauss magnets seem harmless enough ? Many variables here including air psi. Different PSI’s do affect how the spindle reacts based on my direct experience and discussed here already. Eddy Current with a floating model My experience with the stock ET2 and 2.5 spindles – I am no scientist – is the higher the PSI the less force required with magnets and the smoother (the motion will be). I use 19 PSI. The ease with which the spindle goes through the manifold at higher PSI is obvious. Try 3 psi and 20 psi to prove this. I have also said this before here - When my cartridge is raised and at rest – at 19 psi - I can blow on it and it will shoot across the top of the LP. Also whether it is a 2.5 or 2.0 spindle. I would assume that the 2.0 spindle being smaller reacts more to less magnets? But the differences could be subtle? Richard – did you have the lead slug in your spindle when you were using the magnets and was it at 12 PSI? Cheers |
