Eminent Technology ET-2 Tonearm Owners

Hi Dover, thanks for your clarifying comments!
Regarding the pressure compensation, it might help to use the analogy of a stiff power supply (air supply & reserve connected to manifold) with a few local supplies (local pressure zones around air capillary openings to the bearing) coupled with high series resistance (capillaries). As current (air flow) drops on one of the sub-supplies, the voltage (air pressure) rises - kind of a passive feedback!
Regarding the usually alluded inherent "stiffness" of mechanical bearings including unipivots, it's worth to consider the following thought:
No material is stiff, everything is more or less elastic. (With some unique properties subsummized in the poetic word "character", importantly damping, and including speed of transmission). Reduce pressure area, and elasticity increases. This affects resonance frequency inherent in any elasticity / mass combo. *Point* coupling as in a unipivot or a spike point, looked at on an "atomic level", is in no way making the coupling stiff, it's the opposite. The surfaces meet in kind of a balanced force & elasticity state, a bit like a jelly ball swimming in water, to put it to the extreme. You don't get steel more elastic than with a perfectly pointed unipivot interface. Then think "it" as an elongated point and you see something like a short subminiature "string" at the end of the point - quite elastic, like a very small piece of microscopic harpsichord string. "Flatter" points like balls have much less of this, and make stiffer bearings - that depend more on extremely complex polishing processes. Some arms use the tip of a roller pen, quite clever!
The whole "argument" (rather a mythical marketing image?) of the "mechanical diode" is moot. Point coupling shurely does "something" (as everything we do does) but shurely it is not "stiff coupling" or magic diode processes. It might eliminate eg. multi-point rattling by a multitude of low pressure indefinite points, eliminating noises of "buzzing paper on a comb"-effects, tingling in metal-to-metal sonority.
And... air bearings are at the total other end of the scale!
That's what Bruce tells us since a long time.

A question to all:
Does anyone have tried grounding the air supply's static charge?
I think Richard mentioned that he connected the brass of the pressure gauge to ground (which ground, where?).
Has anybody else tried it?
There are - expensive - antistatic "hoses" available. Would be interesting to try, maybe even only on the short distance between the last air tank (preferably antistatic & grounded too) and the arm.
Other grounding ideas? Like putting a copper grid into the air tank and potting the grounding wire in hot glue?
BTW my simple air tank is a 20 gallon fuel "canister" (unused :-) with a long and a short aquarium tube entering the cover of the tank reaching the top and the bottom), the whole sealed by hot glue and padded with acrylic wool. Very simple , cheap and working well.

Pegasus
Yes air supply is grounded by earthing the brass threaded part of the pressure gauge that touches the air stream. I have tried this earthing remote from the arm and close to the arm. Close is best in my setup.
Theory is that the air builds static as it flows thru the tube.
A second test, recently repeated was to place a large ferrite bead over the air tube close to the arm. This caused a dramatic negative change.

Go figure.

Cheers

Pegasus
Sorry didn't answer your question.
Air stream grounded to the house wiring earth.

Cheers

***** ET2 THREAD - BEARING STIFFNESS STICKY DISCUSSION *******

Just so this info does not get lost here. :^)

Pegasus

Regarding the pressure compensation, it might help to use the analogy of a stiff power supply (air supply & reserve connected to manifold) with a few local supplies (local pressure zones around air capillary openings to the bearing) coupled with high series resistance (capillaries). As current (air flow) drops on one of the sub-supplies, the voltage (air pressure) rises - kind of a passive feedback!
Regarding the usually alluded inherent "stiffness" of mechanical bearings including unipivots, it's worth to consider the following thought:
No material is stiff, everything is more or less elastic. (With some unique properties subsummized in the poetic word "character", importantly damping, and including speed of transmission). Reduce pressure area, and elasticity increases. This affects resonance frequency inherent in any elasticity / mass combo. *Point* coupling as in a unipivot or a spike point, looked at on an "atomic level", is in no way making the coupling stiff, it's the opposite. The surfaces meet in kind of a balanced force & elasticity state, a bit like a jelly ball swimming in water, to put it to the extreme. You don't get steel more elastic than with a perfectly pointed unipivot interface. Then think "it" as an elongated point and you see something like a short subminiature "string" at the end of the point - quite elastic, like a very small piece of microscopic harpsichord string. "Flatter" points like balls have much less of this, and make stiffer bearings - that depend more on extremely complex polishing processes. Some arms use the tip of a roller pen, quite clever!
The whole "argument" (rather a mythical marketing image?) of the "mechanical diode" is moot. Point coupling shurely does "something" (as everything we do does) but shurely it is not "stiff coupling" or magic diode processes. It might eliminate eg. multi-point rattling by a multitude of low pressure indefinite points, eliminating noises of "buzzing paper on a comb"-effects, tingling in metal-to-metal sonority.
And... air bearings are at the total other end of the scale!

.

That's what Bruce tells us since a long time.

Yes for a long time page 3 of the ET2 manual.

The large surface of the air bearing uses some of the tightest tolerances in tonearm manufacturing today, and is much more rigid at audio frequencies than metal bearings"

what imagery and a way of expressing things clearly.

a bit like a jelly ball swimming in water, to put it to the extreme.

:^)

Now regarding this statement .......

As current (air flow) drops on one of the sub-supplies, the voltage (air pressure) rises - kind of a passive feedback!

An observation.
When I had my ET 2.0 HP and and ET 2.5 HP both on the same table I switched their air hoses back and forth. With the supply source remaining at a constant 19 PSI, it was interesting to watch the PSI gauge go up by a few PSI when hooked up to the ET 2.0 (into the 20's) and likewise to watch the gauge go back down by a few PSI to 19 with the larger lunged 2.5. Audiogon'r Ketchup has presented graphs here showing similar information.

Relevant info from the Oct 29 Post Sticky.

CT0517
If we use my ET 2.5 as an example that you set up specifically for 19 psi which is your optimum design setting for your tonearm. A continuous 19 psi air flow is sent in. Can we assume the spindle uses all 19 psi to work optimally (or is it a percentage of this amount)

Bruce
The manifold is optimized for the design pressure, the pressure at the surface of the spindle is a percentage of the inlet measurement, this is by design. The ET2 uses roughly half of the air to allow the spindle to work properly ? The supporting force is the surface area of the bearing times the pressure at the surface of the bearing

ME
So allowing air to escape around the edges of the manifold as more is pumped in ? is this a captured air bearing system ?

Bruce
Yes it is captured.