Eminent Technology ET-2 Tonearm Owners

Dover, can you clarify a few points concerning the effective horizontal mass of ET? The manual states that it is 25-35gms. Is this the mass of the wand plus manifold tube, which is then increased by addition of up to 40gms in counterweights?

I understand that the mass of hanging decoupled counterweights behaves differently than fixed counterweights. It would be interesting to have the math on this horizontal pendulum effect. In any case, while the design may lower horizontal inertia to an extent, it will also contribute to horizontal inertia to an extent. I would imagine that the effective horizontal mass of the entire moving system is quite a bit higher than 35gm.

In the course of developing the predecessor of the Trans-Fi tonearm, Poul Ladegaard experimented with a pendulum counterweight. For whatever reason that feature was abandoned.

BTW, with a custom lightened CF slider and wand the horizontal mass of my Terminator totals 35gm. This includes custom front and rear wand counterweights designed to vary the wand's vertical effective mass. On my full-range system with a sub to 18Hz, the lighter horizontal assembly sounds better than the heavy one. Also, variations in vertical effective mass are more impactful than relatively large variations in horizontal mass.

Lots of variables.

Dover.
Magnetic dampening will vary with the speed of horizontal motion..... so does pure mass. The formula F=Ma you quoted in another thread confirms this. Try shaking say a 1kg weight backwards and forwards at 0.55 hz (record hole centering error) and try again at 20 hz, (music). Much more force is required at the higher frequency. If this weren't the case, the R&D dollars speaker driver manufacturers spend on reducing the mass of the moving parts would be for nought. As I said earlier all three dampening methods increase in resistance with rising frequency of excitation.
That said, I agree with you, I do not like the effect of the oil trough.
To be clear, I do like, mostly, what magnetic dampening does. Further it is elegant and kinda cool, but I hear a slight negative which does not exist with the mass approach. As I said, I think that it is caused by induced currents circulating the spindle. Do you really want these currents anywhere near your delicate feed from the cartridge? I would be using mag dampening today if not for this slight negative.
Mag dampening increases cartridge output, yes agree, same holds for mass. My take on this is perhaps different to you. While is reduces micro vibrations which is a good thing, I think that the higher output is because the cartridge has more lateral resistance to work against because it cannot move the arm laterally as much. And move due to the cantilever tracing the groove it must, F=Ma again. More cantilever lateral movement equals more output.

Yes the Dynavector is an arm design that I have studied because it is unusual in using mass and magnetic dampening. But currents near the cartridge output?

Look, I don't actually care if people agree with me on this mass thing. I said earlier that it was contentious. Anyone with a full range system down to the 20s, might want to try it. They could well be surprised at what information is lurking in the grooves.

Dgarretson
Dover, can you clarify a few points concerning the effective horizontal mass of ET? The manual states that it is 25-35gms. Is this the mass of the wand plus manifold tube, which is then increased by addition of up to 40gms in counterweights?

Hi Dave
Page 5 of manual – spindle weight (14 grams) tonearm tube weight (11 gms) plus the counterweights. To give you a reference point I am using one large and one small counterweight with the 420 str. That should be 20 gms.

Page 9
‘By decoupling the counterweights horizontally but not vertically, the mass of the counterweight is not seen by the cartridge above a certain frequency and is lowered. This allows use of heavier (more rigid) components in tonearm design with increasing effective mass. Decoupling mechanism is damped at a 2 – 5hz.”

Maybe Dover, Richard or others can add more regarding the horizontal inertia.

"lots of variables"

YUP :^)

Cheers

but I hear a slight negative which does not exist with the mass approach. As I said, I think that it is caused by induced currents circulating the spindle.

Hi Richard - Did you try the magnetic damping on belt drive or string drive as well ?

Do you really want these currents anywhere near your delicate feed from the cartridge?

Richard – in your opinion what would you consider as “near your delicate feed”. Reason I ask.

The two little circle magnets I use with my ET 2.5 - the closest one is a good 7 or 8 inches away from where the wire exits the armtube – when at the the end of the record which is the worst case.

I should note I am using copper on the ET 2.5 right now. I have silver on the ET 2.0 that is on a brass armpod. No room for trying magnets there.

Looking at my analog gear its obvious I am not afraid of magnets.

I know some who think magnets cause cancer.

Can you give some details on how to go about making that lead slug for inside the spindle?

Cheers Chris

Chris.

While I have built a number of BD turntables, they all employed pivoted arms.

The eddy currents induced by the magnet are everywhere within the spindle since it is conductive, so having the magnets at the opposite end to the wand does not take them any further away from the cartridge signal. Therefore it is "near". The negative effect was apparent before and after I changed the goose neck to conductive aluminuium.

I made the internal slug by rolling up 1/2mm thick lead sheet strips. Cut to different widths. The roll OD was equal to just less than the ID of the spindle. Different widths gave me the ability to experiment with different weights.
A string was passed thru the center of this roll and thru 1/4" plastic tubes like that used for the air feed. String tied off one end and a length left at the other. The tubes were cut to length such that one tube protruded a few mm once the tube/lead/tube assembly was slid inside the spindle. Thus when the counter weight end cap was reinstalled it slightly compressed the tubes. Tubes were equal length to position the lead in the centre of the spindle. The pull string allowed the whole assembly to be removed.

Everything causes cancer.