Eminent Technology ET-2 Tonearm Owners

Richard, interesting comments. Eventhough I settled on 18.5 -19 psi (at the arm) based on what my ears tell me sounds best in my system and not simply what my HP manifold was designed for, that pressure is (coincidentally?) about .5 psi above the pressure at which the check valve on my surge tank starts to release some air without fully opening. As the pressure is increased further the released air increases until the spring loaded valve opens fully (at about 20.5 psi or so AT THE SURGE TANK). Makes me wonder if the reason the arm sounds best at that pressure is not only that it is the ideal pressure for my arm, but also that the released air has a similar effect as what the Motronix accomplishes. Thoughts?

Frogman.

I suspect that the check valve you refer to is actually a safety relief valve. And yes it could be the same thing that I am hearing.
It may have an adjustment so you could, entirely at your own risk :-) increase its setting to see if the bleed flow could be stopped but still maintain the same pressure out of the regulator and on to the arm.
Obviously I don't know what your surge tank can take in terms of max pressure, so be careful should you decide to do this.

I read the TAS review and this could be a review of the changes I hear in my system. It is a significant jump in performance and ultra easy to do.
The dimensions given for Motronix unit would imply that any surge tank, if included, would be very small indeed. So maybe it is simply two high quality regulators with a central bleed?

It shows how sensitive the arm is to smooth air delivery. As per my earlier post, the compressor had cycled off, so the air supply was coming only from the reserve in the tank. The "noise" in the air stream could only be coming from the regulators and the associated hosing to the arm.

Richardkrebs, yes, safety relief valve, I have always incorrectly referred to it as a check valve. Interesting proposition. My DIY PVC tank can handle the full output of my Medo compressor which although rated at 22psi can actually output close to 30psi. Dave has the same compressor and it outputs 32 psi. Prior to installing the relief valve I tried higher pressures (without controlled air bleed) but I did not like the sound which would take on an overly lean and rather tense quality. I settled on 18-19 psi for best sound. I don't think that the relief valve can be adjusted, but it would be interesting to hear what higher pressure with controlled air needing sounds like.

Richardkrebs and readers of this thread,

My apologies to all for not having responded earlier, neurosurgery has precedence.

Richardkrebs has been advocating changes to the ET2 that include adding mass and removing the patented decoupled counterweight. These suggested changes take the ET2 outside of its designed operating parameters.

In February Richardkrebs promulgated a theory that adding 30g+ of lead to the ET2.
He also advocated removing the decoupled counterweight and changing it to a fixed counterweight assembly. He claimed that this was a big improvement on the performance of the ET2 with low compliance cartridges. Richardkrebs claimed to be the only authority on adding lead mass to the ET2. Richardkrebs claimed that adding lead mass and removing the decoupling gave a flat frequency response in his listening room.

To recap…

Richardkrebs on adding mass:

02-15-13: Richardkrebs
I have added a lead slug inside the bearing spindle 25 mm long with its OD equalling the ID of the tube…
This combined with the fixed counterweight means that the arm is HEAVY in the horizontal plane. I have tried magnetic dampening and oil troughs but prefer the pure mass approach. I run at around 12 psi, lower pressures may be problematic when adding so much mass.

03-03-13: Richardkrebs
For those of you who may be interested in adding mass. I would bring your attention to Morch's latest arm which uses massive weights to increase horizontal mass.....Extra weight like this would dwarf the 30 or so grams I have added to my ET.

NOTE : This post demonstrates a lack of understanding. Removing the decoupling of the counterweight also increases that horizontal mass that the cartridge sees and therefore the total increase in mass would exceed the 30g claimed.

03-04-13: Richardkrebs
I have tried both light and heavy ETs. As far as I can tell, I am the only one who has done that. If so, I am the only person here who can speak with any authority on the subject.

Richardkrebs now claims that he has NOT added 30g off mass after all, and that his arm is close to the standard weight.

12-09-13: Richardkrebs
My ET spring a leak, actually one of the o'rings failed. This necessitated disassembly. I took the opportunity to give it a spring clean and weigh it. Total weight excluding cartridge was 86 grams (95 grams with cartridge). I have on loan a standard I beam, counter weight assembly (thank you Grant) this weighs in at 47 grams, excluding the spindle clamp. This would put the total weight of a standard ET2 up to 77 grams with an aluminium wand and 85 grams with a magnesium wand. It is my intention to revisit the use of a sprung counterweight.

12-10-13: Richardkrebs
The 30 gm adder was a guess based on 16 year old memory. Clearly my guess was well overstated. I will be removing this when I do the swing arm counterweight test to bring the arm as close to stock as possible. The 95 gm total, arm and cart weight, is accurate. This depending upon c/weights and cart used by others, being more or less the same as a standard ET2 using a mag wand.

It would appear that the sonic benefits Richardkrebs proclaimed, accompanied by much mathematical conjecture over the past 10 months, are not attributable to adding lead mass as Richardkrebs claimed, and that the benefits of adding lead mass, if any, exist only in his head, in theory, as they have not in fact been trialed.

With regard to the Morch analogy, this is speculation and assumptive on his part by his own admission. Rotational inertia is quite different to linear inertia and I’m not sure how one could possibly use a pivoted arm model to explain the forces involved in a linear tracking tonearm.

For what its worth, I too have experimented with lead mass. I made a lead slug, 25mm long and fitting the ID of the ET2 as per Richardkrebs suggestion. Excluding the string and glue, the mass varied from 26gm to 34gm depending on how tight the slug was wound. Richardkrebs now claims that his arm is only 7gm heavier than standard. I cannot replicate his new claim of a mass differential of 7g with the size of lead slug he advocated.

05-15-13: Richardkrebs
My calculation of weight delta was based on how much weight the air bearing has to carry

Clearly Richardkrebs calculations were incorrect since he has not added anywhere near the amount of lead mass that he believed he had.

Richardkrebs on removing the patented decoupling system on the counterweight:

03-25-13: Richardkrebs
I know that BT designed the arm to have the two spring systems, Cart and Counterweight. I just don't think that it is a good idea….

02-17-13: Richardkrebs
I did my initial tests on extra horozontal mass by disabelling the leaf springs on the counterweight beam

03-20-13: Richardkrebs
The thought that there may be more going on with the decoupled counterweight was triggered by your post where you quoted BT where he said that the ibeam had a natural frequency of 2-5 hz.
This is close to the resonant frequency of the arm itself. This could have performance implications.

03-21-13: Richardkrebs
If fixed, the counterweight beam must be very strong…. Three springs don't cut it.
It is no accident that other arm manufacturers have a rigid joint there....it simply sounds better.

03-25-13: Richardkrebs
Has anyone thought about why the CW spring(s) and their damping are so fussy to set up?
My prime reason for fixing the counterweight is to restore the full bass drive….

04-16-13: Richardkrebs
When I fixed the CW and added further mass and used a low compliance cart, there was an unexplained positive side effect. Focus and sharpness improved. Transients were better. It was some years ago when I made this change and while liking the improvement, I didn't put too much thought into 'why'.

I will not be degrading my arm by converting it back to standard form.

From Richardkrebs posts it would appear that he removed the decoupling spring, but did not understand the implications. Bruce’s testing on the Eminent Technology website demonstrates a rise in low frequency resonances if the decoupling is removed.

Despite this Richardkrebs clearly states that he disagrees with Bruces ET2 design goals of maintaining a low horizontal mass and using a bifurcated spring to split the resonant frequencies to minimize resonant peaks in the low frequencies.

Here is an extract from Bruce’s patent on the ET2.

The damped leaf spring 39 is oriented so as to allow horizontal motion but prevent vertical motion, i.e., decoupling, of the counterweight arm 37 and counterweights 38. Decoupling is necessary to reduce the effective mass seen by the cartridge 36 in the horizontal plane which allows the use of high compliance cartridges 36. The stiffness of the damped leaf spring 39 can be increased to allow higher horizontal mass to match low compliance cartridges 36. The damper material for the leaf spring 39 can be an elastomer. Damping provides the desirable quality of little or no rise in amplitude at resonance horizontally. Also separate horizontal and vertical resonant frequencies can be achieved by decoupling only in one plane of motion.

Removal of the spring decoupling will increase the resonant peak – Bruce measures 6db plus. If you go though the Shure white papers on low frequency resonance, they confirm this – they measure resonant peaks of 6-20db that increase motion 2 to 10 times.

From the Shure white papers -

what happens at the resonance frequency? One important characteristic of resonance is that motions are magnified considerably, in this case, typically from 2 to 10 times.

In both situations, the output from resonance frequency signals in the groove will be increased from 6 to 20 dB. These numbers are just the dB equivalent of the magnification numbers previously mentioned. By itself, this may not be all bad, since this resonance peak determines the low-frequency response "limit" of the pickup and system, and a bit of boost here may not be unpleasant. This was certainly true fifteen years ago, when arm resonance frequencies of 30 to 50 Hz were common. However, with modern pickups and arms, these resonance frequencies are usually subsonic (below 20 Hz), so that reproduction by the loudspeakers may cause distortion. Additionally, preamp overload is most likely to occur at boosted low frequencies since the preamp clipping level is lowest here. Consequently, the arm resonance has lost whatever usefulness it once had and must now be regarded as a liability.

The most pernicious effect of the resonance is shown in Figures 1 and 2 by the "scrubbing" notion developed by the stylus in the groove. This causes program material to warble in pitch, just as if the turntable speed were fluctuating. In fact, the groove speed is changing (relative to the tip), because a fraction of the velocity of arm vibration is added to the groove velocity. (See Appendix I.) The effect is that about 1/3 of the arm vibration velocity is alternately added to and subtracted from the groove speed. For example, at arm resonance, total amplitudes of 1/32" are easily observed by eye. If the frequency is 8 Hz (typical for high compliance pickups and average arms), the resonance velocity will be about 2 cm/sec (see Appendix II). This velocity will produce a "scrubbing" velocity of 0.6 cm/sec along the groove axis. The groove speed at a 4.5 inch radius is about 40 cm/sec; so the frequency modulation will be about 0.6/40 = 1.5% and easily audible.

Another less obvious consequence of the arm resonance is that the stylus force is "used up" when the arm is vibrating. In the previous example, if the compliance of the pickup is assumed to be 20 x 10-6 cm/dyne, 2.0 grams of stylus force will be required to accommodate the arm vibration alone. This is larger than the usual stylus force, so mistracking is quite certain at the extremes of the vibration.

Clearly the removal of the decoupling has negative impacts on both tracking and increased distortion in amplifiers and speakers from the infrasonic distortion generated by the cartridge/arm resonance.

Use of Fluid Damping

Again there are more contradictions in Richardkrebs posts -

02-18-13: Richardkrebs
I do not like the effect of the oil trough.

05-05-13: Richardkrebs
Twenty years ago I made a oil damping trough for the then standard ET2, mounted on a Goldmund Studio.
installed it on the current arm. Nice changes to the blackness of the background. The system is even quieter. As a result, it doesn't seem to extend dynamics upwards but downwards further into the low level detail. A very agreeable effect. Also greater presence and focus. It will be staying. .

Richardkrebs on Stiffness of the Air Bearing

04-21-13: Richardkrebs
....the air bearing employed on these arms is effectively rigid at audio frequencies. So they should look elsewhere when looking for the cause of compromised note leading edge performance. .

This is a very good example of conflating physics and mathematics.
Frogman, Ct0517, DGarretson, Slaw, myself and many others hear significant differences in performance when adjusting the air pressure on the ET2.

Having studied structural, mechanical and materials engineering and physics at university, my view is that altering the air pressure will alter the performance of the arm – either altering the rigidity and/or altering the resonances within the air bearing.

I quote Ralph Karsten of Atmasphere producer of valve amplifiers, and who has considerable experience producing and cutting records.

01-17-12: Atmasphere
If LPs were perfectly concentric like they are supposed to be, I can imagine that having a high lateral tracking mass would have its advantages. But in real life, concentricity is something that we hope for and often come very close to getting, but its not perfect. IOW the arm does need to negotiate such imperfections in the LP. I imagine some of the issues can be tuned out with the leaf-spring device mentioned earlier- so does that mean that you have a different setting depending on the LP?

One other issue of air bearings I forgot to mention is the coupling that needs to occur from the platter surface to the arm tube of the arm. The idea is that the arm and the platter move together as a single unit. That is to say that if there is air-borne vibration, it affects the platter in the same amplitude and phase as it does the base of the tone arm. If there are differences between the two, this will be heard as some sort of artifact, IOW it becomes something that the cartridge can react to. This is why the plinth can have such an affect on the sound of the 'table.

When you have an air bearing, this coupling is not as profound as it should be. One of the demonstrations that this is a very real phenomena is the fact that as you increase air pressure in the bearing (increasing coupling to the base) the arm sounds better.

When I questioned the stiffness of the bearing in relation to the added mass Richardkrebs advocates, he responded -

03-19-13: Richardkrebs
Re quality factor, Q. ... under, critically or overdamped systems, as they relate to the ET2. My running the arm at 12 psi is no accident. I addressed the Q factor of my arm years ago. And the bearing has no issues at all carrying the extra weight, even at this pressure.

And yet now he says he is running 18psi.

11-05-13: Richardkrebs
The output is fed thru two regulators in series, bringing the pressure down to 18 psi for the arm. .

In summary then, despite having owned the ET2 for over 25 years, it would appear that since February this year -

Richardkrebs has advocated adding lots of lead mass, and claimed many benefits, but now claims that his ET2 arm mass is close to standard.

Richardkrebs has proclaimed that Bruce’s decoupled counterweight is not a good idea, and stated in April that putting the arm back to standard will degrade the sound. Now, in December, Richardkrebs is not sure and is going to retrial the decoupled counterweight.

For 25 years, Richardkrebs eschewed fluid damping, but now believes it is of benefit.

Richardkrebs claims the ET2 air bearing is rigid at audio frequencies and 12psi was the optimum air pressure for his set up, having carefully calculated Q. Now he has moved up to 18psi without an explanation.

These contradictions outlined above, demonstrate a lack of scientific rigour in testing and set up. It is not an approach that one would recommend.

It would appear that Richardkrebs has much work to do to determine the optimum set up for his ET2. My suggestion would be for him to put his arm back to standard and set it up as per Bruce Thigpens’ ET2 manual, assuming he now has some understanding of how it works.

For your reference here are links to the Manuals and Patent
http://www.patexia.com/us-patents/04628500
http://www.eminent-tech.com/main.html

Seasons greetings to all..

Dover

Received my ET package from Bruce yesterday.
Will post up pictures over the weekend of my air set up along with the ET-2.5 on my system page.

Hi Rugyboogie
your Christmas present hath come early..no?
You must have been really good this year
But aren't you supposed to wait until the 25th to open the box ? :^)
They say its better to give than to receive; if so BT must be feeling pretty good this year.
Congrats and looking forward to your impressions.
Cheers