Eminent Technology ET-2 Tonearm Owners

Thank you Chris, Dover, Richard, and all for the fascinating data, opinions, and food for thought. I continue to enjoy the, admittedly, subtle effects of using a single weak magnet with my ET.

I can't claim to understand the physics involved well enough to give a thorough explanation of what happened in my particular case, but I have to concur with Dover about the concerns over added mass. In my case, it was not mass in the spindle, but a case of too much mass at the "headshell" and cartridge itself. A few years ago I managed to destroy the suspension on one of my VDH cartridges by applying too many bits of Blu-tac to a "naked" MC1, and to the top of the headshell in an attempt to dampen a cartridge that sounded overly aggressive in the highs. It worked to smooth out the ragged highs, but within days, experienced a collapsed suspension. The cartridge was properly balanced and setup at the appropriate VTF.

****Does damping not mean - reduce, diminish, dull - to a point that reduces some of “vinyl’s nasties”, caused mostly in this case with the ET2 tonearm – the off center hole - but we want to do this without taking away too much from the music itself ?**** -Chris

In the endless debate about wether footers, pads, etc. have a beneficial effect on music playback accuracy, I have always contended that, in absolute terms, it is not possible to overdamp a component's resonances by adding mass. Added mass can only be a good thing; in theory. While it may be possible to tweak the resonances to suit a particular system or listener's tastes, eliminating/controlling resonances can only be a good thing for a component's electrical performance, if not it's role in a given "system" (including the listener's ears) which is functioning in the electrical domain. But, it seems to me that in the case of a tonearm, we are not talking about simple resonances, but how added or removed mass affects the movement and stability-in-motion of the arm/cantilever "system". Sorry for possibly stating the obvious, but it helps me to make better sense of all this. Thanks again for a most interesting discussion.

Frogman.
I enjoyed your post, thankyou. How much blutac did you add to the headshell? By way of comparison I have added a net 0.77gm to the headshell of the ET2. (Lead in, teflon out.) Not a lot of extra weight.

On damping... If it is not meant to move, make sure it doesn't.

To everyone..I'm sure that you have experienced this. Last night's listening was great. All the planets seemed to align. So what causes this? Clean power? Just the right room temp, humidity? My own state of mind? Off topic, I know, but I am curious to read your views on this.

thanks
Richard.

Hi Frogman,

Thanks for the feedback. You have highlighted the nub of the issue in your last few sentences - when the arm moves laterally to accommodate eccentric records it becomes very complex. In addition to the bearing tube moving back and forth we have -

1. The arm mass pushing the cantilever back and forth through its pivot point
2. The counterweight, if partially decoupled with a spring, starts to oscillate as the bearing tube moves back and forth.

My approach to the problem has 3 elements all of which work together -

1. Lighten the arm to minimize resistance to lateral movement. Remove any soft spongy material - shrink wrap/foam if using the old aluminum arm tube.
2. TOTALLY decouple the counterweight ( no spring, no fixed coupling )
3. Minimal magnetic damping

Counterweight Set Up

In my view fixed, coupled counterweight is wrong because it adds inertia, a resistance to any correction for eccentric records.
I also think a spring is suboptimal, because although by tuning it we get a lower resistance, and maybe better bottom end on round records, on eccentric records the in and out motion means the counterweight will oscillate and feed back into the bearing tube, affecting its horizontal stability.
I would surmise that when you tune the spring, you are probably synchronizing the motion of the counterweight with the arm motion to minimise these conflicting forces. This will vary with the cartridge compliance and how eccentric the record is.
With both coupling and spring ( partial coupling ) the arm movement is inhibited – causing cantilever flex that is disconsonant with the music.

The key question is - What do we want the counterweight to do on eccentric records ?
The answer in my view is nothing.
We want it to continue to load the tracking force.
We want it to remain absolutely still horizontally whilst the arm moves in and out so it does not inhibit the arm movement. ( we don’t want the tail wagging the dog ).
Think of a hinged counterweight, rigid vertically, but free to move so that when the arm moves the counterweight stays still.
My solution was to remove the spring action by loosening off the end cap such that the counterweight beam just flopped at a touch; then inserted teflon wedges loosely either side of the spring to provide the tiniest dampening of that I could apply.

The combination of the "floppy" counterweight in the horizontal direction and minimal magnetic dampening gave me the best result – very quick bottom end.
A bass drum has harmonics and overtones up in to the high frequencies – the highs tell you how a drum is hit – so for me I trade off a little bottom end weight for accurate, clean and extended high frequencies.
Funnily enough this approach gives me the quickest and most tuneful bass.

How much magnetic damping to apply ?

My experience is as little as possible. What I have found is that I set the amount effectively by tuning the bass for optimum speed. Remember that the eccentric arm movement is affecting all frequencies. The dampening will affect all frequencies.
My view is that if you use too much magnetic dampening you will stiffen up the bottom end, but at a cost over over dampening the high frequencies. That’s why I was interested in Chris testing the eddy clamp – which I suspect is just too much.

I wanted to clarify that for me the use of minimal magnetic damping goes hand in hand with how I set the counterweight up and the low mass/minimal resistance.

Here is Bruce's opinion on using ET2 manifold shims

On 3/5/2013 10:05 AM,
Hi Bruce

We would like your opinion on the small space between the ends of the manifold and the rubber rings.
You can slide the edge of a piece of paper in there.
Is it by design for resonance control - to achieve a certain frequency ?
If shims are inserted in there - does this not in theory make the setup more rigid - desirable?
Would this affect the general frequency resonances of the ET2?
We look forward to your opinion on this. thanks. Chris

Chris,

The o-ring is used as a seal, when the manifold is inserted, the ring is flattened and the gap is taken up, that is the design intent.
The science of resonance in a phonograph tonearm would first involve a measurement to prove something exists. This is very easy, Take another ET2 tonearm and use its cartridge to play the tonearm under test. Compare the levels of record playback to the measured level of vibration on the tonearm under test using a spectrum analyzer. If the vibration levels measured are greater than -50dB below playback levels then there may be something significant and you might call it a resonance.
Odds are good that the manifold has no significant vibration levels from a stylus forcing function while playing a record. I hope this helps.

brucet

Richard, Dover, others ?

When Bruce says:

“science of resonance in a phonograph tonearm would first involve a measurement to prove something exists.”

Curious if magnetic and mass damping, and any of its effects can be measured other than just by listening ? Have you done it?

Chris -
No I dont have the equipment, but Martin Colloms did in a Hifi News review years ago ( 1985, I think ). He measured the resonances before and after the air bearing and compared them to ascertain how the air bearing dealt with such. Typically you would use an accelerometer placed on either the arm or bearing housing to measure these.
If my memory serves me well the resonance profile remained in tact, in other words even though the resonance is passing through air and rubber, it went through almost unhindered.

By the way - another little tweak for you - I decoupled the rotating arm lift from its bracket using teflon washers/spacers, another small audible improvement.