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:
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.
Richardkrebs on removing the patented decoupling system on the counterweight:
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.
From the Shure white papers -
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 -
Richardkrebs on Stiffness of the Air Bearing
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.
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
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: RichardkrebsNOTE : 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.
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.
03-04-13: RichardkrebsRichardkrebs now claims that he has NOT added 30g off mass after all, and that his arm is close to the standard weight.
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.
12-09-13: RichardkrebsIt 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.
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.
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: RichardkrebsClearly Richardkrebs calculations were incorrect since he has not added anywhere near the amount of lead mass that he believed he had.
My calculation of weight delta was based on how much weight the air bearing has to carry
Richardkrebs on removing the patented decoupling system on the counterweight:
03-25-13: RichardkrebsFrom 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.
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.
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: AtmasphereWhen I questioned the stiffness of the bearing in relation to the added mass Richardkrebs advocates, he responded -
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.
03-19-13: RichardkrebsAnd yet now he says he is running 18psi.
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.
11-05-13: RichardkrebsIn summary then, despite having owned the ET2 for over 25 years, it would appear that since February this year -
The output is fed thru two regulators in series, bringing the pressure down to 18 psi for the arm. .
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