Eminent Technology ET-2 Tonearm Owners

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. I first did this test some 16 years ago and preferred a fixed counter weight. Before I made the decision to change, I considered the ramifications of such a move. One parameter which was looked at was tracking of eccentric records. I did not want to damage my cartridge and records with the stylus slewing about in the groove.

With this issue, resonance theory saved the day.

A way back in this thread, I posted a transmissibility graph. I had hoped that this would resolve the discussion. This shows structural movement for various excitation frequencies above and below a given resonance frequency. The resonance frequency of the counterweight assembly ranges from 2 to 5 hz. The excitation frequency from an eccentric record at 33 rpm is 0.55 hz.
If we apply this 0.55 hz input to the sprung counterweight arm, we can see what happens... transmissibility approaches 1. This means that the whole structure moves. The cartridge "sees" the counterweight.
Lets put this clearly. When tracking an eccentric record with a standard ET2, the stylus/cantilever is required to accelerate sideways, 1320 times per LP side, the TOTAL weight of the arm; wand, gooseneck, spindle, cartridge, PLUS I beam and counterweights. Depending upon the counterweights used and the weight of the cartridge, this total can approach 100 grams. The same ball park as my arm.

Just wanted to add a couple of thoughts re the HP manifold. In a couple of the previous posts there appeared to be the suggestion that the HP manifold was not necessarily a worthwhile upgrade over the original LP manifold. Dave has corroborated what I have always felt: that the HP version is very worthwhile and a very significant upgrade over the LP version. After living with the LP version for several years before upgrading to the HP, I am confident that Dave's experience mirrors mine. I bring this up since the 2.5 manifold is no longer available, so this is an interesting option for all owners of the ET2 for a very reasonable price. Of course, the pump/compressor has to be a suitable one.

12-09-13: Richardkrebs
Depending upon the counterweights used and the weight of the cartridge, this total can approach 100 grams. The same ball park as my arm.

You have stated in earlier posts that you added 30g of lead to your ET2 plus lead to the headshell and replaced the original plastic counterweight beam with an M10 threaded rod. You have strongly advocated adding more mass to the ET2.
It is simply not possible to add 30 plus grams of lead and arrive at the same net weight to an unmolested ET2.

With my low compliance Denon 103 weighing 9 gms I could balance the ET2 with 35g at the counterweight giving a total mass of around 79 grams. ( That would be about 43 gms using your maths ).

Re your comments on transmissibility -

03-14-13: Richardkrebs
Shown here is a link to the Math on driven harmonic oscillators, a mathematical representation of an arm/ cartridge assembly. It shows in both formula and graphical terms what I have been trying to say. The Math is a bit of a struggle but fortunately the graphs show the results.

en.wikipedia#Driven_harmonic_oscillators

I have pointed out before, the model you refer to applies to a harmonic oscillator like a pendulum. You are incorrect if you think that this represents a cartridge.

The arm/cartridge/record interface has 2 fulcrum points -
The stylus point around which the cantilever pivots, constrained by the groove.
The cantilever suspension point, about which the cantilever also pivots, but which is partially constrained by the rubber suspension damping.

The forces involved are double ended - you have the groove applying a force to one end of the cantilever via the stylus. The other end of the cantilever has forces being applied from the arm motion.
The 2 forces are not in sync because there is a suspension joint between the cantilever and the arm.

In order to conceptualise this, think of 2 people holding a pipe and each one trying to move it sideways out of sync with the other. That is what the cantilever experiences. It is not a pendulum and it is not a harmonic oscillator.

The Wikipaedia example you have chosen does not apply.

Rather than get lost in fanciful mathematics the bottom line is that the cantilever flexes when faced with an eccentric record, even more so with added lead mass.
I quote Bruce Thigpen directly

the cartridge will "see" .55Hz mounted in any tonearm, more so in one with higher horizontal inertia
I don't think Kuzma means the stylus does not deflect at all at .55Hz, that would defy physics

Postulating that the cantilever does not flex with an eccentric record and that adding mass has no impact defies physics.

Hi Richard

" spring cleaning ? "

I wish. its freezing here.
where to put the Christmas tree for best room acoustics in a shared room ?

I am interested in your I Beam testing/findings.

Is your manifold a standard low pressure one ?
If so consider including tests that use just enough PSI to make the spindle float and work as Bruce designed.
I think Dave's recent observations on music presentation when PSI is run higher on a regular LP 2.0, show how much we change change things up with PSI. This will change your findings/results.

I am also interested to know what your and others definition is of a really eccentric record ?

I believe we are all different in what we will tolerate as far as this is concerned.

Wouldn't it be nice if someone came up with a record making machine that could produce holes in vinyl - LIKE A CD.

Looking at the way the groove looks.

http://embrangleroot.files.wordpress.com/2012/08/tumblr_m7ob01afye1qlixleo1_1280.jpg?w=614

Now add an off centered hole to that mess.