Eminent Technology ET-2 Tonearm Owners

Manitunc – just a note on my last post.

If it works its the original ET2 manifold. If it needs a higher pressure to work you have a HP manifold.

If we are talking about an older ET2 arm it may need more pressure because of it being dirty. Its a good idea to clean inside the manifold first. Slide out the spindle and use a toothbrush with alcohol and scrub the inside of the manifold. See page 40 of manual. This is an easy enough procedure and highly recommended for anyone buying a used ET2 with no history.

Cheers

Thekong.
It should be no surprise that the arm weighs in at that figure or even higher with the heavier counterweights. It is neccessary for it to perform well with low compliance carts. This provided that appropriate damping is applied. Lead out wires, air tube, and maybe an oil trough.
An obsessive designer like Andy Payor would have taken this weight factor into consideration.
I agree, it would seem that the Kuzma is indeed a lot heavier, based on its appearance. That said, maybe it uses carbon fibre and other weight saving techniques?

05-13-13: Richardkrebs
Thekong.
It should be no surprise that the arm weighs in at that figure or even higher with the heavier counterweights. It is neccessary for it to perform well with low compliance carts.

This is not correct with respect to the ET2. In my experience adding mass to the ET2 with low compliance cartridges reduces the speed, articulation, transparency and harmonic structure of the music.
Increasing mass with the ET2 also increases tracking distortion and can result in a bass hump of 6-12db by loading up the cartridge with high mass.

A quote direct from Bruce Thigpen

Bruce Thigpen
If the weight is coupled the system resonant frequency would be extremely low, a resonant frequency at 3Hz with a significant rise in response (6-12dB) results, which would affect tracking slightly because of the asymmetric position of the cantilever, we opt for splitting the horizontal resonance frequency into two points and lowering the "Q" which improves tracking.
More important than tracking, the intent was to reduce the modulation effects of low frequency energy (FM and AM) that increase distortion in the cartridge

Quote from ET2 Manual – Bruce Thigpen

P29
It is desirable in most cases ( low to medium compliance cartridges 5x10 dynes/cm – 20x10 dynes/cm ) to use the minimum number of weights, far out on the cantilever stem. This decreases the horizontal inertia of the tonearm while increasing its vertical inertia.

Adding mass to the ET2 increases the inertia to lateral movement and on eccentric records will result in increased cantilever flex and distortion.
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. This is what Bruce Thigpen is saying.

Furthermore, with higher mass, once the arm starts moving, the lateral movement is undamped. Cartridge overshoot and uncontrolled cantilever flex are inevitable. This explains why when Richardkrebs added fluid damping the sound appeared to be better controlled or in his words had “greater presence and focus”.
This is because the addition of lead mass and removal of the decoupling mechanism from the I Beam in his ET2 pushes the horizontal mass too high and the cartridge cantilever motion goes out of control. He would be better off reducing the horizontal effective mass by removing the lead he added to his arm and putting back the decoupling in the I Beam that he removed.

If you go to the Eminent Technology website and read the ET1 manual (that’s the arm that precedes the ET2) you will discover that the ET2 was a design decision to move away from the high mass/fixed counterweight model utilized in the design of the ET1 to the low mass decoupled counterweight model utilized in the ET2. These new design considerations embodied in the ET2 resulted in substantive improvements in the quality of sound reproduction.

The decoupled I-beam methodology employed by Bruce Thigpen in the ET2 is designed to minimize horizontal mass and ensure that the resonance of the I-beam and counterweight remains below the horizontal resonance of the arm so that the 2 resonances (arm and beam) do not couple together to produce a large peak resonance in the bass.

The horizontal effective mass for a linear air bearing arm is the sum of the mass of the bits that move sideways.
The ET2 reduces this mass by decoupling the counterweight. We all clearly understand this design feature. The benefit of this approach is to reduce the amplitude of Fr
The bearing design makes no difference to the effective mass or the resultant Fr. There is nothing particularly unique about the ET2 bearing. The cartridge still has to push this mass sideways. Either a relatively low mass with the ET2 or heavier with a Rockport , Kuzma, Walker or Krebs arms. In an undamped system with a fixed counterweight we see a large rise in amplitude at resonance. This is easy to control with damping. For a good discussion on this see CT0517's post on 01-12-12
Open the attachment and read pages 18-19 and 24-26.
The graph on page 25 shows how this peak is completely removed by adding an oil through. The subsonic peak has gone and provided Fr is low enough, so has its effect on the audio spectrum. In this paper Bruce talks about the effect being noticeable at 3x Fr. Way back in this thread I talked about the effect of resonance being present at up to 6x Fr. We use this safety factor in our designs in my business.
It is this effect that led me to fix the counterweight. With a stiff cartridge; the only way to get Fr low enough to avoid interaction with audio frequencies was to make the arm heavier. The Fr of my arm/cart is 5.2 Hz. Thekong's setup is a little under 5hz. In Fremer's review of the Kuzma he set it up with a Fr of 5 hz. This is no coincidence , we all set up our systems with effectively the same Fr, safely 4x below the audio spectrum. My point is that the Fr needs to be around 5-6 hz. To avoid this interaction. With a high compliance cart this target is achievable with a standard ET2, it cannot be achieved with a low compliance cart. At least 3 respected designers agree with me.

In past I have damped the resonant peak by adjusting the air pressure and deliberately dressing the lead out wires to damp horizontal movement. This method is fussy and not particularly robust. Adding the oil trough has solved these problems and allowed me to push the pressure back up. 17 psi seems optimum in my rig.

There have been concerns raised about the extra weight I have added pushing the bearing outside it's design spec.
I am using the original wand less its heat shrink wrap plus a lead headshell insert. Say the same weight. I am using an aluminum goose neck which eliminates one cap screw and the short lifter arm. I have also eliminated the male wiring plug and used a lighter grub screw instead of a cap screw for the gooseneck wand clamp. Say same weight.
I have fixed the counterweight and eliminated the I beam the brass threaded weight, several cap screws and the locking slider assembly. Say same weight.
My counterweight is 32 grams.
I have added 30 grams of lead inside the spindle in the center of working travel, such that it does not leave the bearing sleeve when tracking modulated grooves.
The ET2 can be optioned with the heavier magnesium wand. 8 gms heavier.
It comes with up to 40 gms of counterweight. 8 gms heavier.
In terms of bearing load carrying capability I have added 30 gm to a lightly configured ET2. If we option it with the magnesium and use all the supplied weights my weight adder is now reduced to 14 grams.
I use a Shelter Harmony at 9 grams. There are cartridges in the 16-17 gm range. If one of these was used the my weight adder shrinks to around 6 gms. It would be inconceivable that Bruce would design a bearing that could not take this small additional weight.

Richardkrebs - For a good discussion on this see CT0517's post on 01-12-12
Open the attachment and read pages 18-19 and 24-26. The graph on page 25 shows how this peak is completely removed by adding an oil through.

ET2 damping trough

Bruce why didn’t you number the pages ?!!!