Eminent Technology ET-2 Tonearm Owners

@ketchup 

Thats why I still run the aluminium arm tube with heat shrink and internal damping removed - keeps the horizontal mass as low as possible and less smear with the h/s & foam removed.

Bear in mind that you are not comparing a Dynavector 17D to an Acutex 420.
You are comparing a "Dynavector 17D plus Bob's Cinemag 3440 MC transformer" to an Acutex 420.

Chris - since I am not running the ET at present, would be good if you could test the eddy current clamp I describe in the above post, using 2 magnets clamping the tube at one point in "S-N Beam N-S" configuration.

10-29-14: Ct0517
*** YELLOW STICKY FOR ET2 THREAD MARK - AIR SUPPLY ***

I had a quick read of your post. A few comments to clarify some misconceptions :

In an aerostatic compensated air bearing as used in the ET the bearing stiffness is a function of
Bearing surface area
Air Gap
Pressure
Compensation

Changes to any of these parameters will alter the "stiffness".

The air gap provides a restriction - on one side you have high air pressure and the other side is lower ( atmosphere ). Air will attempt to flow from the high to low pressure - the escaping air creates the air bearing.

Compensation is where you have a second restrictor between the air supply and air gap (bearing) - in this case this is the capillaries. The function of the capillaries is to
1. Distribute the air over the bearing surface in an optimum manner to get a stable air bearing.
2. Restrict the air flow to the bearing.

By restricting the air flow to the air bearing a reserve is created in the manifold. For example if a load on the bearing reduces the air gap at the bearing, flow is reduced. The reserve pressure that had been held back by the capillaries now allows for increased pressure in the gap, creating a restoring force that gives the air bearing stiffness.

As a general rule when compensation is used the pressure in the bearing is about 50% of the supply pressure.

Bruces comments regards to the quality of air and flow reflect that compensation has a greater impact on bearing stiffness than pressure.

Any restriction or damage to the capillaries or indeed scratches on the bearing surface could compromise the bearing stiffness to a significant degree. Hence your comments about maintenance are very pertinent.

The Air Bearing Spindle psi requirements are less than the manifold as only a portion of this air is required for it to float properly. Approximately 50%. That means on a base ET2 only 1.5 psi ! - if your manifold is restored and functional.

The "old" air escapes as per Bruce' design out the sides of the manifold.

Not really. As explained above a higher pressure is required in the manifold to provide a reserve air pressure using compensation. A leaky manifold would not be helpful. In my experience putting too much pressure through the ET2 pushes so much air out of the air gap between the spindle and manifold bushing the arm cannot reach the end of the record. At some point the rubber seals might leak but this has not been apparent.

Regarding bearing stiffness.
The main advantage of an air bearing compared to ball race or roller bearings as used in most tonearms is twofold -
1. Virtually no friction in the air bearing. In rolling bearings, the static coefficient of friction is higher than the dynamic coefficient of friction. In other words it takes more force to initiate motion than it does to maintain motion. In air bearings the static and dynamic coefficient of friction are the same. So the air bearing has a quicker response to changes required from the cartridge tracking.
2. Surface irregularities in the roller bearing surfaces mean that the rotational tracking is uneven compared to an air bearing.

Now in terms of conventional pivoted arms, most have roller bearings for both horizontal and vertical motion. Some "knife edge" tonearms such as the old SME's have knife edges for vertical motion, but still have roller bearings in the arm pillar for horizontal motion.

True unipivot tonearms have a simple point contact for both horizontal and vertical motion, so they are much closer to an air bearing than they are to a conventional gimbal arm using roller bearings. Because the unipivot has a point load, "bearing stiffness" is not an issue.

Coming back the ET some contributors have commented that with increased pressure the bearing tube arm is harder to pull out of kilter( and hence the comment the bearing is stiffer ). What actually happens is if you pull the air bearing tube perpendicular to the bearing you are closing the air gap on one side. The escaping air ( from high pressure manifold through the bearing to atmosphere ) will try to find the path of least resistance - which in this case will be the bigger gap. Basically the air bearing will collapse. Increasing the pressure will help.

Mods for ET2
Removed heatshrink from arm tube
Removed foam from arm tube
Removed teflon filler from headshell and replaced with carbon fibre
Had stiffer bracket that joins armtube to bearing tube manufactured
Replaced wire with van den hul silver - hello radio campus ( rf )
Replaced wire with copper litz from Sumiko tonearm box, hung below pivot and soldered directly into MIT cable approx 2' behind the bearing tube in the centre of the range of movement
Placed small cupboard door magnet under bearing tube - this provides electromagnetic dampening on eccentric records.

All of these were good improvements. I have found any sort of dampening other than the magnetic described slugs the sound.

Oh and using an isolation transformer on the air pumps, running 2 air pumps out of phase to double the airflow and surge tanks.

Away on holiday so can't do pics at moment

Hi Ct0517, I'm very rusty since its about 15 years since I used the ET2, but from memory I had an I beam with a thin metal strip at the bearing tube end. I packed soft strip ( might have used thin lead or teflon ) either side of the thin metal bit that goes into the bracket on the end of the bearing tube and then played around with the tightness of the clamp - I was able to vary the lossiness of the I beam from rigid to virtually floating. Then I settled the point that gave the most natural bass soundwise with air around it.
Re the magnetic dampening, I used a small cupboard door magnet and simply placed it on the turntable plinth with a packer to get the magnet as close to the bearing tube ( the moving one ) without touching it. This magnetic dampening is used by Dynavector on their tonearms where a curved horizontal metal near the counterweight moves through 2 magnets above and below it as the tonearm transverses the record.

Frogman - yes. Ed Thigpen's response at the time was "he's probably right".
Dgarretson, I use to check the level on my ET2 by balancing it to 0 with an additional counterweight and checking that when nudged the arm would travel freely and the same distance in both directions from centre. This as well as a level on top of the tube. Possibly a string bias weight type of weight pulling on the end of the armtube may be "gentler" than tilting the arm in your instance ??.

Ketchup, I used the ET2 before the magnesium arm wand came out. The arm was smooth and gumetal grey under the shrinkwrap. !st I removed the heatshrink, more agile sound, then I removed the foam inside the arm tube - lighter sound but much more transparent.
For the cartridge mount I carefully prised open the end of the arm, enough to get long nosed pliers onto the soft insert and pulled it out. Then I got a thin piece of carbin fibre, cut to size, then inserted it into arm with araldite and clamped the headshell until dry.
I never compared this to the magnesium arm.
Cheers

Apbiii - Martin Colloms did some testing of energy transmission in the ET2 years ago. He measured the resonances in the arm tube and then in the arm after the air bearing. The conclusions were that the unwanted energy transmitted went straight through the air bearing and out the other end relatively unimpeded.
This is the old chestnut - do you kill unwanted energy by overdampening, or by having a drain path to ground ( the plinth ).
The main issue with overdampening is that soft materials eg rubber, will store energy and then release it "out of time" with the music, thus smearing the sound.
People will have their own preferences, do you want to hear everything, quick, coherent, lively if a little coloured, or do you like a nice smooth inoffensive sound if lacking a little speed, detail and coherence.

From the arm tube to the plinth and the energy resonances measured were very close, ie transmission rate was very high.

Although I'm no longer using the ET2 at the moment, one record I found that is readily attainable is Joe Jackson's Jumping Jive. On the track titled "Five guys named Moe" there is a part where Moe is repeated 5 times. With the ET2 you can clearly hear each utterance and the position, starts front slightly right of centre and each "moe" is behind and to the left of each preceding one. The ET2 is the only arm I have found that captures this positioning in space so clearly.

Hi all,
I'm a big fan pof the ET2 modded even though I dont run it, went to unipivot primarily to get rid of pumps etc. You have to read the thread in WBF, I simply cannot believe the sheer ignorance of many of the contributors, the worst being Astor and Lavigne. Not much hope for credible audio reviews from these folk. These guys are idiots and I doubt much of their gear is set up correctly from their lack of understanding of basic physics.

http://www.whatsbestforum.com/showthread.php?5653-Linear-tracking-Turntables!

PS If you have low tolerance levels dont bother reading it. Make sure you have your sense of humour on board.

Ct0517,
What interested me, or should I say piqued me, was the comments on lack of bass with ET2. I have run and listened to extensively the ET2 on the following TT's - Sota/Sota Star/Roksan/Townsend/Goldmund Studio/Technics SP10mk3/Final Audio. I was clearly getting more bass extension with some decks than others with the same cartridge/system, which tells me that the ET2 was not the limiting factor in bass extension. With some of the TT's the bass notes would "flat spot", in other words organ and double bass notes rather than go down further down the scale, the lowest notes would play incorrectly.

Now here is a poser for all you guys -
An engineer/mathematician friend of mine suggested many years ago that if you run a tangential tracking tonearm and set the stylus exactly on the tangent, then the stylus has no reference as it has no lateral forces acting upon it and hence it is unstable. ( for those of you old enough think old fashioned cars with kingpins and wobbly steering when centered ).
His proposal was that if you run a tangential tracking arm then you should run a tiny amount of overhang and tracking angle on the cartridge.
Thoughts anyone...

Ct0517 - I would not run an ET downhill, but I get the overhang argument.

NOW HERE IS ANOTHER POSER to ponder :

With a pivoted arm we have an overhang. The pivot arm/stylus tip moves in an arc, which means that for every 1.8 seconds ( 1 rotation ) the stylus tip has actually moved slightly forward with each rotation.
Put another way if you put the stylus tip in the first groove, and draw a tangent to the spindle centre, then with each rotation the stylus tip will move further ahead from that tangent.

This means that to achieve the correct playback speed, with a pivoted arm, then the TT needs to speed up with each rotation.

This means that the only playback system that is accurate in terms of speed is in fact a linear tracker.

Now...thoughts...

Another tip from downunder - I found plugging the pumps into isolation transformers rather than directly into the mains smoothed the sound out quite a lot even with dual pumps/surge tank etc.

Last one I saw sold for US$2500 on Ebay only a few months ago, cant remember what arm it had on it. So the thing is worth about $5-6k, plus some premium for condition. Based on the sellers perception of value maybe I should offer him my Final Audio for $20k plus the Nakamichi. I think the CT would be better.

Slaw -
With regard to the aluminium plate/acrylic. I would not run the plate, it's added resonance. I have moved away from metal spikes, and if I use them I radius the tip so it is not a sharp point. I say radius, as in rounded, NOT flat. The idea is a small radius tip sitting in a larger radius hole as per most unipivot bearings. My suggestion would be to radius the tip of the grubs screws and then you should be able to couple directly to the acrylic without damaging the surface. In an ideal world the acrylic would have a dimple in it for the radius tip to sit in.

Thanks Chris - I would take up your offer, but alas I cant get the ET back yet. I am having to play the long game on this one. I would be happy to throw it on the Fidelity Research FR64S/Dynavector DV501/Naim Aro if you are interested.

Ct0517
Fyi the Final Audio TT uses a 35mm thick slab of superplastic zinc ( SPZ ) for the "plinth" - weight of plinth exclusive of platter/bearing/armpod/arm is approx 40kg. The inverted bearing and armpod are bolted directly to this slab. Info is here :
http://books.google.co.nz/books?id=ohQdU5ggcOIC&pg=PA143&lpg=PA143&dq=superplastic+zinc+(SPZ)&source=bl&ots=uDqm8e0JsG&sig=oPdsNcyBUypOB6D9VWdrx_vFdgQ&hl=en#v=onepage&q=superplastic%20zinc%20(SPZ)&f=false
The base is tight and quick.
My experience is that slate does ring. A friend of mine is now working on a ultra lightweight composite powdered ceramic sandwhich plinth for the Garrard 301 to try a "non stored energy" approach having discarded slate/panzerholz etc.

Hi Slaw - here are a few suggestions for you to consider -
Wiring loom - I would untwist the wire between the arm and plinth to reduce resistance. I would also place the anchor point for the cable on the plinth at the midway point of travel, not the end.
I do not subscribe to separate pods for arms, the arm must be rigidly referenced to the bearing point. Your use of rollerballs in the TT with a separate pod would be a disaster in my view.
Use your woodwork skills on the speakers - pulling the crossovers out of the box, even without changing any components, will yield a significant improvement in resolution and lower noise floor.

Ct0517 - I last used my ET2 with a Garrot modified Denon 103. Also used Koetsu Black & Shure V15VMR.
As far as springs go, I really didn't use the spring effect at all. I found that even with low compliance cartridges, when you reduced the horizontal compliance, the bottom end tightened up, but became more and more out of time with the music. TT at the time was a heavily modded Sota Star. The solution I ended up with was leaving the end cap only partially done up, and used teflon wedges partially inserted either side of the "spring" to a point where the initial movement had almost no restriction whatsoever, but the range was limited and ultimately tempered by the teflon. This with the magnetic dampening explained in my earlier post yielded the best results with both high and low compliance cartridges. I guess what I ended up with was virtually a decoupled counterweight assembly with a very gentle progressive dampening via the teflon wedges.

Frogman -
I got considerably more transparency and even less grain when I removed the inner foam and stripped off the heatshrink from the aluminium arm tube with both low compliance ( Denon 103 Garrott ) and high compliance ( Shure V15VMR ) cartridges.
Also I suggested implementing electromagnetic dampening of lateral movement by using fridge magnets early in this post - disappointingly for me, only ct0517 has tried it - a $5 tweak that stabilises the cartridges so much, you get increased output and have to turn the volume down. The dampening increases proportionally with lateral arm movement speed.
By the way magnesium has a lower Youngs Modulus than aluminium, which means it is much softer and less rigid ceteris parabus.
If you want to go one step further, you can open up the cartridge end of the wand ( the aluminium is very thin ), pull out the soft teflon insert, and replace it with a piece of carbon fiber. You can use superglue and clamp it up with a decent vice. This gives you a much stiffer headshell.

Frogman - the order I went through was -
1st removed inner foam - listening test
2nd removed heatshrink - listening test
3rd modified head shell - listening test
4th added electrodampening - listening test
My personal view on fluid dampening is that it slugs/smears the sound, as does spongy dampening such as foam/heatshrink.
Your experience with the Spectral MCR mirrors mine.
I would suggest you disengage the dampening trough first - so you can hear the other changes more clearly.
Good luck.

Chris, hi there,
Thats exactly where I ended up with the Shure V15 - 1 lead weight far far out.
I think with the electrodampening of the lateral tube motion and decoupling of the beam in place, even low compliance cartridges benefit from least weight furtherest out approach.

Nandric - I'm an honorary member of the ET2 club having owned one for many years since the 80's. Unfortunately in a moment of madness I gave it to a friend who bought my old Roksan TT. It will come back eventually.

Nandric - do you have a ranking for your MC's at this stage. Am very interested to hear what you think of the Magic Diamond. The Kiseki Silver Spot I know well so if you do a comparison to that then I can work it out from there.

Hi Chris/Grant
Yes I used 2 pumps running into a 20 litre surge tank. On the pumps I used, reversing phase & neutral at the transformer inside reversed the phase on one of the pumps. In NZ you must not reverse phase and neutral at the power cord because the mains fuse must be in the phase line.

Ct0517 - fyi
Magnets can be a little eccentric. On Richardkrebs deck they may prefer the wand end because they get a better view of the cantilever doing her one legged tantric yoga exercises.

You've just reminded me - I got a big improvement when I put an isolation transformer between the mains and the pumps. Much smoother sound.

Richardkrebs

Re: your ET2 mods. Here are a few points for you to consider.

I have a view on linear arms in that the rules for pivoted arms and effective horizontal mass do not apply. In fact I have added a lead slug inside the bearing spindle 25 mm long…
This combined with the fixed counterweight means that the arm is HEAVY in the horizontal plane.

This view is indeed strange. Many records are off centre. By increasing the horizontal mass of the arm significantly, when you play an eccentric record the increased resistance to motion from the additional mass will result in increased cantilever flex. On eccentric records your approach will result in phase anomalies during play back, increased record wear and probably cartridge damage in the long term.
My ET2 has been lightened, no internal dampening, no external tube dampening, decoupled counterweight and have had no issues tracking low compliance cartridges, achieving extended bottom end with speed, articulation and accurate timbre. Magnetic dampening controls lateral motion on eccentric records.

The arm is optimized for low compliance carts. As you can see, just, from one of the pics Ketchup found, it has a fixed counterweight.

I have found the opposite. Using various Koetsu’s and a Denon 103 Garrott I found that there is an optimum decoupling point. Eliminating the decoupling resulted in more “apparent” bass but with less speed, articulation and timbre. In my decoupling methodology I used teflon pads either side of the spring with the end cap quite loose. This gave a soft lossy quality to the motion as opposed to springy.

On the magnetic dampening front the negative I heard was possibly caused by the induced circulating currents interfering with the cartridge output

I could not hear any distortions of this nature with the magnets located on the opposite side of the manifold from the cartridge wand and using copper litz arm wiring that exited before the gooseneck and straight into the phono 12” away.

Cartridge leads are single strand silver lightly twisted at about one turn per 8 mm. Continuous to the preamp

Highly prone to rf, might explain your perceived issues with magnetic dampening.

Have removed the Teflon in the head shell and replaced with a square of 1/2 mm thick lead and super glued in place.

With low compliance cartridges, there is significant energy generated for the arm to deal with. This energy needs to be wicked away from the cartridge and sunk to ground. To maximize this energy flow away from the cartridge materials should be used that that successively increase propagation speed heading towards ground. This encourages the energy flow away and minimizes reflection of energy back towards the cartridge.
Inserting lead into the head shell creates an energy reservoir that will sink energy, but due to the softness of the lead some will be released back into the cartridge out of time with the music. The same argument applies to the use of a lead slug in the bearing tube. This causes smearing and loss of detail. I would not recommend the use of lead.

One other question I have on your SP10mk3. You mentioned you are using an acrylic/lead/acrylic plinth. It appears from the photos that you have bolted the motor to the bottom piece of acrylic and the ET2 to the upper piece of acrylic, with the lead layer in between. If so this would compromise the loop rigidity between cartridge/arm/platter required for accurate playback.

Hi Chris - yes I agree with Thigpens comments, but I think Richardkrebs high mass approach throws away the advantage of the ET2 over other tangential arms, that is the light horizontal mass. The ET2 is less than 25gm compared to the 80g of the Terminator. The effective horizontal mass of the ET2 is even lower with a decoupled counterweight. The other problem with adding mass to the ET2 is that not all low compliance cartridges are created equal, as the compliance in the horizontal plane cannot be assumed to be the same. For example the Denon 103 is far more rigid in the horizontal mode than the Koetsu even though they are similar compliance vertically.

Richardkrebs/Chris :
Magnetic Dampening vs Mass.

I have been away on business and my responses have been brief. I can now expand on my previous comments.

With a lower mass the arm will move more rapidly initially to align with the eccentricity of the record, minimising cantilever flex.
The magnetic dampening only commences its action once the arm starts moving, and is proportional to the rate of movement. I should point out that the dampening is created by eddy currents which are only generated when the arm moves relative to the magnet.

By contrast, adding mass means the arm will not move until the driving force from the eccentricity is enough to overcome the higher inertia. This increased resistance to movement from the added mass means that the cartridge cantilever is forced to deflect to keep the stylus in the groove. This defeats the purpose and advantage of an air bearing tonearm - the uninhibited degree of freedom to accurately track the groove.

This higher mass is not dampening, it is increased inertia - a resistance to movement.
Magnetic dampening is dampening the arm motion once the arm has commenced movement.

I'll restate this :
Magnetic dampening allows the cartridge to move to the correct position in a damped fashion.
High mass means the arm wont initially move, inducing the cantilever to bend.

Any excessive cantilever deflection in a moving coil will result in phase anomalies as the coils attached to the cantilever are driven into a position where the response becomes non linear.

Furthermore, with the higher mass, once the arm starts moving, the lateral movement is undamped. Cartridge overshoot and more cantilever flex is inevitable.
With magnetic dampening the lateral movement of the arm is always damped when moving.

John47 - you misunderstand how it works. It is not magnetism that provides the dampening. It is the eddy currents created when the arm moves across the magnet. Read this
http://en.wikipedia.org/wiki/Eddy_current

Eddy currents (also called Foucault currents[1]) are electric currents induced within conductors by a changing magnetic field in the conductor. These circulating eddies of current have inductance and thus induce magnetic fields. These fields can cause repulsive, attractive,[2] propulsion, drag and heating effects.

Frogman - I used a cupboard door magnet. It had a pair of magnetic plates implanted edge on. You see 2 parallel edges exposed in a plastic case. I placed these on the plinth, under the bearing tube with the edges in line with the bearing tube, next to the manifold, on the other side of the manifold from the cartridge. Like this ( looking down the bearing tube )

O bearing tube
!! magnet(s)
-- plinth

Note that my modified arm cable loom exits the arm wand in front of the bearing tube, it does not pass though the bearing tube.

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.

Hi Chris, thanks for the complement. Yes I do try to be flexible. I am contemplating a post grad course in pseudo science at the Massachusetts Institute of Technology. This may help me comprehend some of the recent posts on the forum.

Yeah I got all that the first time. We'll never agree on the added mass approach. But anyone trying it should check their cantilever deflection on eccentric records to ensure the cartridge can cope.
I'm sceptical on the degree of movement in the bearing, but if there is movement then stylus drag will pull the bearing tube forward on that side of the air manifold.

IMPORTANT NOTE for Frogman/Chris
What folk need to know is that if you use 2 magnets either side of the tube ( forming an eddy current clamp ), the dampening will increase disproportionately. I have seen controlled studies where dampening of unwanted energy has reduced by 80+% with 2 magnets either side of a beam instead of 1. You place the magnets S-N Beam N-S

Your ultimate solution if you want maximum dampening would be 4 magnets, 2 pairs either side of the manifold in the "S-N Beam N-S configuration".

I could argue that if you use 2 magnets in a clamp arrangement, you might be better off clamping the counterweight end and letting the stylus drag of the wand pull that end of the bearing tube against the bearing wall naturally. That way you dont have conflicting forces created by the eddy currents and stylus drag fighting on the wand side.

When positioning magnets for eddy current dampening, closer is not always better, the magnetism has nodes that vary up and down with distance.

Chris - Thanks for the feedback. I always thought shagging around with the system was housework. Out of interest do you run your Verdier with or without the ball inserted ?

Hi Chris - Yes I have a good memory. When we first imported a pile of ET2's we had in the shop an ET1. There was a big debate at the time that the ET2 had less bottom end than the ET1. The ET1 has a fixed counterweight. My business partner preferred the counterweight bolted up as per the ET1, but I found that gave a one note bottom end, lacking speed and articulation.
I experimented with the counterweight coupling and other ET2 mods quite extensively not only with a variety of TT's including Sota Star Vacuum, Townsend Rock, Roksan, Oracle and Final Audio TT, but also a variety of speakers including Martin Logan CLS, Apogees, Proac EBS, Proac Tablettes, Duntech's, vintage Tannoy Monitor Golds and many others - over the last 30 years.
Also have run the ET2 specifically with a wide variety of cartridges including Madrigal Carnegie, various Koetsu's, Van den hul Grashopper, Shinnon Red, Sumiko Talismans/Virtuoso's, Shure V15VMR, Denon 103 Garrott, Benz Reference and many others I've long forgotten.
I have also seen enough off centre cantilevers to last a lifetime from the misapplication of both tangential and pivoted arms.

Richardkrebs

para 1 - not obvious to everyone.
You are testing the effect of magnetic damping with an ET2 with rigid counterweight and high mass. Chris has been testing magnetic damping with partially decoupled counterweight and no added mass as has Frogman.

I have not said that mass, mag damping and fluid damping are the same other than that they all resist motion and that this resistance increass with frequency.

This simplistic view fails to differentiate between inertia and damping of motion.
During the course of this debate over the last few weeks you dont seem to comprehend the difference between inertia and damping of motion.

Inertia is the resistance to a change in its state of motion or rest. When you add lead to your ET tonearm you increase inertia. By increasing inertia the cantilever will flex more on eccentric records.
Damping is the retardation of motion once the movement has commenced. This means the cartridge can move straight away with an eccentric record, which results in minimal flex in the cantilever, and less distortion, but eddy currents generated by the motion of the arm relative to the magnet retards the oscillation of the arm and cartridge.

Adding lead mass creates higher inertia but does NOT retard motion.
Magnetic dampening has lower inertia and dampens motion.

I repeat again that the lead mass that you have added puts more load on the cantilever when the arm tries to move to accommodate an eccentric record.

Furthermore, with the higher mass of the added lead, when the arm moves there is more momentum, there is no control over this mass, and there is no damping of motion to minimize overshoot as the arm tries to correct.

As viewed by the cantilever this is no different to me adding mass in the linear plane to the ET.

Again - a very simplistic view of the world. Pivoted arms have tracking error and offset angle. The physics is quite different to that of a linear arm.

Adding mass

but Morch with their flywheel do not appear to have reached that point nor have I with my arm.

This is an assumption and speculative.
I could just as easily surmise that the Morch arm is so thin and lacking in structural integrity that it needs added mass and fluid dampening to control energy and resonances in the arm generated by a good moving coil cartridge.
Conventional mathematics says that adding mass to a flywheel, not only increases inertia, but it is harder to slow down. You are making the problem of navigating an eccentric record bigger than it needs to be.

Chris -
No I dont have the equipment, but Martin Colloms did in a Hifi News review years ago ( 1985, I think ). He measured the resonances before and after the air bearing and compared them to ascertain how the air bearing dealt with such. Typically you would use an accelerometer placed on either the arm or bearing housing to measure these.
If my memory serves me well the resonance profile remained in tact, in other words even though the resonance is passing through air and rubber, it went through almost unhindered.

By the way - another little tweak for you - I decoupled the rotating arm lift from its bracket using teflon washers/spacers, another small audible improvement.

Chris, the good thing is, if we have a bad day over here we can fly over to your place and start the day again ...

Hi Frogman,

Thanks for the feedback. You have highlighted the nub of the issue in your last few sentences - when the arm moves laterally to accommodate eccentric records it becomes very complex. In addition to the bearing tube moving back and forth we have -

1. The arm mass pushing the cantilever back and forth through its pivot point
2. The counterweight, if partially decoupled with a spring, starts to oscillate as the bearing tube moves back and forth.

My approach to the problem has 3 elements all of which work together -

1. Lighten the arm to minimize resistance to lateral movement. Remove any soft spongy material - shrink wrap/foam if using the old aluminum arm tube.
2. TOTALLY decouple the counterweight ( no spring, no fixed coupling )
3. Minimal magnetic damping

Counterweight Set Up

In my view fixed, coupled counterweight is wrong because it adds inertia, a resistance to any correction for eccentric records.
I also think a spring is suboptimal, because although by tuning it we get a lower resistance, and maybe better bottom end on round records, on eccentric records the in and out motion means the counterweight will oscillate and feed back into the bearing tube, affecting its horizontal stability.
I would surmise that when you tune the spring, you are probably synchronizing the motion of the counterweight with the arm motion to minimise these conflicting forces. This will vary with the cartridge compliance and how eccentric the record is.
With both coupling and spring ( partial coupling ) the arm movement is inhibited – causing cantilever flex that is disconsonant with the music.

The key question is - What do we want the counterweight to do on eccentric records ?
The answer in my view is nothing.
We want it to continue to load the tracking force.
We want it to remain absolutely still horizontally whilst the arm moves in and out so it does not inhibit the arm movement. ( we don’t want the tail wagging the dog ).
Think of a hinged counterweight, rigid vertically, but free to move so that when the arm moves the counterweight stays still.
My solution was to remove the spring action by loosening off the end cap such that the counterweight beam just flopped at a touch; then inserted teflon wedges loosely either side of the spring to provide the tiniest dampening of that I could apply.

The combination of the "floppy" counterweight in the horizontal direction and minimal magnetic dampening gave me the best result – very quick bottom end.
A bass drum has harmonics and overtones up in to the high frequencies – the highs tell you how a drum is hit – so for me I trade off a little bottom end weight for accurate, clean and extended high frequencies.
Funnily enough this approach gives me the quickest and most tuneful bass.

How much magnetic damping to apply ?

My experience is as little as possible. What I have found is that I set the amount effectively by tuning the bass for optimum speed. Remember that the eccentric arm movement is affecting all frequencies. The dampening will affect all frequencies.
My view is that if you use too much magnetic dampening you will stiffen up the bottom end, but at a cost over over dampening the high frequencies. That’s why I was interested in Chris testing the eddy clamp – which I suspect is just too much.

I wanted to clarify that for me the use of minimal magnetic damping goes hand in hand with how I set the counterweight up and the low mass/minimal resistance.

Thekong

Thanks for sharing your experience. I agree with Fremer.
Thigpen does appear to hold patents on the decoupled counterweight.
Whereas Walker uses a fixed counterweight at 45psi in the Proscenium, Richardkrebs advocates using a fixed counterweight, adding additional lead weights and running a relatively low pressure of only 12psi in his ET2.
In my view his modifications increase inertia and increase the loading on the cantilever suspension when side forces from eccentric records are presented to the stylus. He employs no dampening to control this increased mass. Once it moves there is more induced cantilever flex from overshoot. This is way outside Bruce Thigpens original design concept of low mass and decoupled counterweight and should in no way be construed to be an ET2. There is always the risk of cartridge and or record damage with Richardkrebs added mass-low pressure approach.
Richardkrebs advice in a previous post for those concerned about possible cartridge and record damage was, quote

People are free to try, it is entirely their choice. Install an alternate cheap cartridge, play a record you don't like, if you are that worried about damage to same.

This advice is probably about the only thing that Richardkrebs and I could agree on.

Thekong,

Yes I agree with you. I only used the 12mm as that was what was used on the Kuzma video Richardkrebs referred to.
The key point as you have indicated is that the Kuzma and Terminator arms will have 3-400% higher lateral force on the cantilever due to their horizontal effective mass being 3-400% higher.
In my view this isn't great and I would worry about using medium to high compliance cartridges with these arms. From your comments I can see you are very careful on setting up your arms.
Will be very interesting to see what you think of the ET2.5 when you have had a chance to set it up. I would encourage you to try my set up recommendations, using my decoupled counterweight suggestion - which means running the I beam very very loose, and tuning the bottom end response by slowly adding dampening to the movement.
Bruce Thigpen has clearly put a lot of thought and experimentation into the decoupling methodology and the low mass.
If you read his manual and patents he starts with a low mass arm, and then brings the effective horizontal mass up very very gently by providing variable spring rates. This is to keep the resonances between horizontal, vertical in sync with the compliance of the cartidge and the Q of the system. The Q is related to the dampening of the oscillation - the use of magnetic dampening will shift this slightly. Very small adjustments can give quite dramatic changes to the sound, especially in speed and articulation.

This post includes feedback from Bruce Thigpen

Dear gentle reader,

Over the past month Richardkrebs has argued the case for adding substantial lead mass to the ET2 and replacing the decoupled counterweight with a fixed counterweight.

In Richardkrebs recommended setup he advocates increasing the horizontal mass by over 300% from 25g to 85g by adding lead to the bearing spindle and coupling the counterweight rigidly to the arm. This is well outside the design parameters carefully formulated by the designer, Bruce Thigpen.

The laws of physics are very simple:

Higher mass = higher inertia ( resistance of the arm to movement )
Higher mass, means that when the arm moves back and forth on eccentric records it places higher lateral forces on the cantilever.

The added lead mass will cause the cantilever to flex more on eccentric records as the arm oscillates in and out.
Furthermore as the arm oscillates back and forth the side loads on the cantilever will increase by over 300%.

I have raised the issue of the additional loads on the cantilever from the added lead mass, and resultant increase in cantilever deflection.

Richardkrebs has consistently denied the laws of physics by claiming there is no deflection because the resonant frequency of the eccentric movement ( 0.55hz ) is below the arms resonant frequency; 3.5-5hz for the unmodified ET2..

To quote Richardkrebs

02-15-13: Richardkrebs
I have a view on linear arms in that the rules for pivoted arms and effective horizontal mass do not apply. In fact I have added a lead slug inside the bearing spindle 25 mm long with its OD equalling the ID of the tube.

03-11-13: Richardkrebs
the resonant frequency due to the combination of a typical low compliance cartridge and horizontal effective mass was in the region of 2.5 -3.5 hz.(this has been published by them elsewhere), this is well above the 0.55 or 0.75 hz for 33 or 45 rpm eccentric records. Therefore the cartridge does not "see" this movement.

03-12-13: Richardkrebs
Below this resonant frequency the cartridge is able to move the arms weight, start it and stop it, without cantilever deflection. I do not need to talk to cartridge manufacturers to confirm this. Do the math.

03-13-13: Richardkrebs
What I have constantly said is that this force will not be enough to deflect the cantilever while tracing an eccentric record, provided the resonant frequency of the arm / cartridge system is above 0.55 hz for a 33 rpm and 0.75 hz for a 45 rpm record.

A fellow Audiogon member has contacted Bruce Thigpen, the designer of the ET2.

Bruce Thigpen has confirmed that Richardkrebs assertion that ‘the cartridge is able to move the arms weight, start it and stop it, without cantilever deflection’ is wrong.

The following are quoted from the correspondence with Bruce Thigpen:

the cartridge will "see" .55Hz mounted in any tonearm, more so in one with higher horizontal inertia

I don't think Kuzma means the stylus does not deflect at all at .55Hz, that would defy physics

I hope this puts an end to this matter as it is becoming boring having to sift through gobbledygook, pseudo science and rubber band conflations.

On the other hand some of the more entertaining highlights posted have been:

Claims that rotational forces of a pivoted arm are the same as the linear forces of a tangential arm

The Morch adds what appears to be considerable mass at a radius out from the pivot point. In so doing they have made a flywheel.
As viewed by the cantilever this is no different to me adding mass in the linear plane to the ET.

Comparing tone arms and cartridges to a rubber band:

All you need is a rubber band representing the cartridge suspension …
The groove modulation is simulated by rapidly moving the rubber band up and down.
Now move the rubber band up and down at a frequency lower than the bounce frequency. This simulates an eccentric record or the lead in, lead out grooves.

Being called a scaremonger

Your scaremongering may have dissuaded people from trying a simple reversible mod

And of course, meeting a legend

I am the only person here who can speak with any authority on the subject.

Bruce Thigpen has clearly put a lot of thought and experience into designing a low mass air bearing arm that includes a decoupled counterweight to optimize the arm and cartridge.
If you read his manual and patents he starts with a low mass arm, and then brings the effective horizontal mass up very gently by providing variable spring rates on the decoupled counterweight. This is formulated to keep the differential resonances between horizontal and vertical in sync with the compliance of the cartridge and the Q of the system. The Q is related to the dampening of the oscillation - the use of magnetic dampening will shift this slightly. Very small adjustments can give quite dramatic changes to the sound, especially in speed, transparency and articulation.

I would not recommend adding lead. Adding mass creates a risk of damage to my expensive and irreplaceable cartridges - Ikeda Kiwame and Dynavector Nova 13D.

For the Richardkrebs of this world – here’s a simple test. It will only take a few minutes. Put your gumboots on and fill them with lead shot. Now try and move your feet sideways, out and in in 1.8 seconds. That’s what your cartridge sees.
Lead filled boots are not required to get the best sound from this outstanding tonearm.

I do not doubt that Richardkrebs beliefs are sincerely held. However they defy physics and are clearly wrong.

Chris -
I assume you know the driving dogs are Kiwis ? NZSPA trained no less, here in Auckland. Not sure if they run ET's, but they demonstrate the benefits of high compliance.
At the Engineering faculty I also remember Dr Fassbender, who had a fetish for experiments with rubber bands -
http://www.youtube.com/watch?v=M0QShhpqtS8

Thekong -

I would ask you to consider the looking at this the other way round. Just because everyone says something sounds the best, is it. Most people thought the world was flat at one time.

My experience with high end audio is that most audiophiles dont hear much and have no sense of timing. Products that produce "impressive" bottom end or top end sell well, and even get reviewed well. Of course it's like car reviews, the next one comes out and all the flaws of the last model get written up.

If we look at the wealthier clientele that Kuzma is targetting, most of them will have large multidriver speakers, eg Wilsons etc. Large full range speakers are incredibly difficult to get coherent in a domestic environment. Alternately we get the wealthy single ended group - these are just tone controls, pleasant, but usually at the expense of speed timing and coherence.

My experience of the higher mass is that it might have a "bigger" bottom end but at what cost in terms of speed and coherence.

Most folk who own these expensive arms are also likely to be changing cartridges regularly - are they really tested. I'm sure some cartridges may be fine, but it's not a given, and the additional forces on the cantilever and stress on the suspension are present, to argue otherwise defies physics.

My ran my ET in the manner it was designed ( decoupled counterweight, no added mass ) simply because it sounded better that way.