05-03-13: Ct0517
Dover - Andy Payor and Bruce Thigpen both disagree with adding mass.
Cant speak for Andy Payor but this is not true with BT. The original ET2 came out when MM’s were popular. When heavier less compliant MC’s became popular. Bruce introduced the heavier 2.5 spindle as well as heavier CF and Magnesium arm wands to deal with MC’s. This has already been discussed here.
http://www.eminent-tech.com/magarmtube.html
thats an old web link btw - the new price for the mag tube is on Bruce's website under Et 2.5 parts list.
A couple of folks here including Frogman and RK have come up with diy solutions. Frogman has used special armtube wrap. RK has added weight to the armtube and spindle. I’m sure others have done other things. Frogman noted as well as BT and myself that the 420str MM seems to gel better with the lighter aluminum armtube. My 420str is now on my ET2.
Ct0517 – my point on adding mass being not desirable is in the context that Richardkrebs has advocated adding 30g of lead to the bearing tube and another 35g by removing the decoupling. Removing the decoupling increases the horizontal effective mass. This is a total of 65g of added horizontal effective mass. Far too much and from what I’ve heard when trialled.
Thigpens own words are to keep the horizontal effective mass as low as possible.
The “heavy” armtube that ET provide for MC’s is not massy.
Bruce advised me that
Bruce Thigpen
Without the wire harness the weights are respectively 13,17, and 19 ("heavy" version of the magnesium tube) grams.
So the heavy armtube is only 2-6g heavier than standard, not 60g as one has advocated. The link states “the new heavy version has over twice the wall thickness of the current magnesium arm tube to reduce the resonance levels in the arm tube “.
This is not to deal with the low compliance per se, it is to deal with the increased energy levels generated from having a low compliance that the armtube has to deal with, its about rigidity. This is similar to part of the rationale for having a decoupled counterweight. Thigpen says it allows him have a heavier and more rigid arm carrier/bearing tube and still keeping the horizontal effective mass as low as possible.
Dover - The Kuzma bearing operates at about 60psi whereas the ET2 bearing operates at a much lower level
Well this is not totally true either – other than the everyday ET2 with the original pumps Bruce would also custom build them for any PSI and did.
Yes I should have used the words “standard ET2” agree with this. I was aware that if Bruce is advised what pump is to be to used he will provide a manifold tailored for that pump.
1) Adding weight to the ET2. As mentioned above and in previous pages here Bruce added weight to the spindle and changed the armtubes for MC’s. If Do-it-yourself (DIY) - adding weight to the spindle and armtube. Consideration needs to be given to vertical and horizontal masses. The ratio is important. Its important to remember that the armtube/armwand affects both the vertical and horizontal masses. .
Excellent point on how adding mass can affect either vertical or horizontal effective masses separately or both depending on where it is added.
The issue that I have is the addition of some 60g to the horizontal mass.
Bruce’s testing and recommendations in his correspondence are to keep the horizontal mass as low as possible, or one will get an unnatural 6-12db lift in the bass, and increased tracking distortion.
2) Decoupled IBeam - The ET2 design is de-coupled. This is a big plus to me right now as it allows me to use any cartridge I want. If you couple it – its no longer an authentic ET2 design. Its your own unique design. Those using it this way seem to have it tailored the setup to one cartridge only? This is their choice.
I have no issue with anyone wanting to do what they like with their system. As someone who has studied engineering at university and has a great respect for Thigpen’s design I take issue where misleading information has been provided or maths wrongly applied to support operating the ET2 outside of it’s design parameters and intended use.
A bigger evil for me than this ....my pivot arms can’t go straight. No one seems to have an issue with this?
It’s like spending thousands on a new car...on the drive home I discover it pulls to the right. I call the dealer about the problem. His/her answer to me is to let some air out of the front left tire. :^(
Would you accept that? Well - All pivot arm owners including me do.
Absolutely agree. But see my leading edge notes below. I love the ET2 when set up properly, but there are some pivoted arms that can provide musical enjoyment as well.
3) Air bearing stiffness. Leading edge notes. My boogie test is older lps up against Master tape dubs – no issues here for me based on my ears. I’m good.
Dover – I am curious to know for fun what your boogie test is?
Chris – these are the words of the reviewer. I would not use the word boogie. My experience is that the Naim Aro, being a mechanically grounded unipivot bearing can reproduce the leading edge far crisper, cleaner and more extended the ET. An example would be percussive instruments. This is typical of well designed unipivots. I have a friend with 2 Graham Phantom’s mounted on a Micro Seiki RX5000 and I hear these same attributes. Even an inexpensive Hadcock can display these attributes – although it is not a true unipivot as the point sits in the apex of 3 balls.
I associate boogie more with the word rhythm and overall musical timing. In this context arm/cartridge matching plays a big part.
The Aro has a narrow operating window – my Dynavector Nova 13D and Denon 103D have better speed, timing and impact on the Aro than with the ET2. The Koetsu Black has more extension in the highs but does not boogie. Whilst it is quick on percussive, has great soundstage & transparency the bottom end timing is awry.
I get fantastic “boogie” with the ET2 when the ET is matched and tuned correctly with the right counterweight location and decoupling employed.The ET2 exhibits better timing and boogie when the horizontal mass is kept as low as possible to optimize groove tracking. If you watch the cantilever the timing goes awry when the cantilever is flexing around on an eccentric record. This is one of the big issues with adding 60g horizontal effective mass.
In my experience adding mass and removing the decoupling destroys the speed, timing and boogie factor.
With regard to springiness – there is an optimum air pressure for the mass at which an air bearing self centres. The design of the air bearing is critical to this, as is the surface area of the bearing and the mass and forces being supported.
http://demo.amplio.si//AmplioCMS2/UserFiles/File/29/theory.pdfThe main problem is that the cushion of air in the gap behaves like a spring. This means that, under dynamic conditions, the cartridge and tube assembly will move in various directions and the cartridge will not stay in the position of the cutter head but will be pulled along the groove and twisted due to the forcesmoving the cartridge in the grooves. Of course this also happens in pivoted arms, but due to differences in construction ie. loose bearings, vibration of bearings and other parts.
To practically avoid this effect we must use a stiff bearing, which automatically reacts to these external forces. Construction of a stiff airbearing is dependent on the air gap, air pressure and bearing surface. Higher air pressure means a stiffer bearing which can carry a heavier load. The same effect can be achieved by a small air gap between the moving parts of the bearing. In the best bearings the gap is limited to a construction of 10 microns. This is actually less than in most pivoted tonearms which have air slack in their bearings to move!!
A stiff bearing will not in itself stop the tonearm bearing from moving closer to one side of the bearing shaft when force is applied to one side. The bearing must be constructed in such a way that it is self-centering. That means, in practice, if force is applied to one end, the gap will decrease but a properly constructed bearing will respond to this by increasing airflow to the smaller gap, restoring the equilibrium.
In practice the gap stays the same if forces are not overloading the bearing and the cartridge position under dynamic conditions remains stable. If we apply force to one end of the bearing sleeve, we have the same problem. To have a self-centering effect along the axis as well as along the diameter of the rod, the airbearing must be properly designed.
This supports my view that if someone adds 60+g of mass to the ET2, not only would they have to increase the bearing stiffness, but would almost certainly have to redesign the bearing itself. This would still not negate the problems of increased distortion from running a higher horizontal effective mass and removing the decoupled counterweight on eccentric records.
