Eminent Technology ET-2 Tonearm Owners

Richard,

It sounds like you have a lot of time into that arm. Very nice! A few months ago I took my ET 2.5 manifold out of the housing to give it a cleaning before I did the flow tests that Chris linked to above and to see how it's built. Upon reassembly, I saw how much give there is in the rubber o-rings and realized that the manifold is not rigidly mounted at all. I thought briefly about a way to stiffen the assembly.

It should be possible to insert three precision shims between the manifold and the manifold housing. They will probably have to be somewhere around .0005" oversized (or less) to get them in without deforming the manifold housing to the point of cracking. Once they're in, there should be no need for set screws which may be a problem for a stock housing. This is not for everyone as you will need a way to slowly creep up to your shim thickness a tenth of a thousandth of an inch at a time unless you happened to get lucky and already have the correct size shim.

Another option is to do what you did (or use three screws instead of one screw and two shims) but put the screw(s) on the inside of the o-rings. A little silicone on the threads may be enough to hold back the 15-20 psi.

Chris,

Nope! It’s got to be a 301 :)

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.

I'm bowing out, while whatever I offered, maybe, somewhat remembered. ( for what, that is for you to determine) Good luck to you all! .... remember the dragonplate... I'm not associated...>

Ketchup
Yes your shim idea is a good one. I wonder if it would be possible to fashion tiny wedge shaped shims and push them in. Could maybe eliminate a bunch of trial and error with individual parallel shims.
And yes I agree, there is considerable compliance in the orings. Also in the original goose neck and arm pillar/ manifold interface.
Chris, yes I have the CAD CAM machines that could make the goose neck and a complete arm. ( excluding spindle and sleeve. ) It would however be costly due to the likely small runs.
The original Counter weight mechanism has been discarded. Adjustment is by means of two knurled discs, either side of the weight, on a M10 threaded rod. You can kinda see this in one of the pics Ketchup found.

Ref horizontal mass, I realize that this is controversial. I simply encourage those of you who feel the urge to try it. Particularly those of you that have full range systems. ( response into the lower 20s )
If we redefine horizontal effective mass as resistance to lateral acceleration we will see that magnetic and oil dampening are similar to " pure mass" all three options resist lateral movement and all three increase this resistance as the lateral movement increases in frequency.
All three impose lateral forces on the cantilever when the record hole is not centered.
The reason that I believe that the rules for horizontal effective mass are different for pivoted and linear arms is this.....
With a pivoted arm the horizontal effective mass in multiplied by the head shell offset. Only a percentage of the cantilevers lateral movement is resisted by the arms horizontal mass in trying to rotate the arm the rest of this movement is resisted by the cantilevers efforts trying to bend the arm tube itself. Linear arms do not impose the second characteristic on the cantilever. This I believe is one reason that the pivoted arm guys complain about a lack of gestalt from linear arms. We largely fix that with oil troughs or magnets. Pure mass is another option

Lead is strategically placed in an ascending hierarchy throughout the arm and TT itself. Tests with a number of soft and hard materials in the head shell and elsewhere convinced me that "local" sinks are beneficial.

While the magnetic dampening was an improvement over the oil trough, it was not as good as the recently added lead slug. It is speculation on my part why this is, but the induced currents seem to be a logical possibility. If they do exist, I suspect that they would be AF in nature, not RF.
I heard this, admittedly, small problem with the original arm wiring, OFC Litz headphone wire I then used and with the silver I now use.
Twisted pairs of wires are less susceptible to RF due to common mode rejection.

In my TT, the arm and motor are rigidly fixed to the same upper acrylic layer.

Dover, are you still running an ET2?

Richardkrebs
With a pivoted arm the horizontal effective mass in multiplied by the head shell offset. Only a percentage of the cantilevers lateral movement is resisted by the arms horizontal mass in trying to rotate the arm the rest of this movement is resisted by the cantilevers efforts trying to bend the arm tube itself. Linear arms do not impose the second characteristic on the cantilever. This I believe is one reason that the pivoted arm guys complain about a lack of gestalt from linear arms. We largely fix that with oil troughs or magnets. Pure mass is another option

Hi Richard – Have you actually measured these forces? I find it very interesting that what you say is supported by information I have from BT on actual testing that he has done with pivot and linear arms. His measurements found that this phenomena (horizontal effective mass, multiplied by the head shell offset and the resulting bending of the cantilever) produced a +6 to 12dB bump between 10-15 Hz versus flat response down to 5Hz (the ET-2).

He also went on to say that “over the years these parameters have been mathematically analyzed and are well understood. There is an easy measurement to prove all of the above, it is called is wow and flutter. If you take the same turntable, put a straight line tonearm arm on it and a pivoted tonearm, both with the same cartridge, the straight line arm will exhibit about half the measured wow and flutter.”

I have his summary findings on this if anyone is interested. Alot of his findings again are in his ET2 manual available publicly.

Some of it was posted here already
here already.

Richard, Dover others ...... any comments on this very basic wow and flutter test ?