Eminent Technology ET-2 Tonearm Owners

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
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

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

I think the home depot link blew the last post up like that.:^(

Just want to clarify when I said.

Richard – did you have the lead slug in your spindle when you were using the magnets and was it at 12 PSI?

I want to recognize that you are running a custom setup spindle/manifold. My experiences have been with stock spindles 2.5 and 2.0.

Still - I assume you tried magnetic damping with the lead slug and without ?

Cheers

Chris, after looking at your picture (thanks) and after thinking about it further, would placing multiple magnets in a straight line not cause the damping to vary as the spindle "sees" additional magnets as it moves toward the rear? What I plan on trying is one single magnet on either side of the manifold, as close as possible to the manifold.

Regards.

Frogman - I have been thinking about that too. Since that pic I have them on top of one another in one pillar. Will try that out. My TT setup does not allow for magnets on both sides as the arm is on a pillar. Look forward to your observations with them on both sides.

Richard, Dover, others - based on your experience if only using the magnets on the counterweight side of the manifold - can u tell me what the most effective arrangement was. I will try various arrangement as well as one larger magnet instead of few smaller ones.