Mods for ET2
Removed heatshrink from arm tube
Removed foam from arm tube
Removed teflon filler from headshell and replaced with carbon fibre
Had stiffer bracket that joins armtube to bearing tube manufactured
Replaced wire with van den hul silver - hello radio campus ( rf )
Replaced wire with copper litz from Sumiko tonearm box, hung below pivot and soldered directly into MIT cable approx 2' behind the bearing tube in the centre of the range of movement
Placed small cupboard door magnet under bearing tube - this provides electromagnetic dampening on eccentric records.
All of these were good improvements. I have found any sort of dampening other than the magnetic described slugs the sound.
Oh and using an isolation transformer on the air pumps, running 2 air pumps out of phase to double the airflow and surge tanks. |
Away on holiday so can't do pics at moment |
Hi Ct0517, I'm very rusty since its about 15 years since I used the ET2, but from memory I had an I beam with a thin metal strip at the bearing tube end. I packed soft strip ( might have used thin lead or teflon ) either side of the thin metal bit that goes into the bracket on the end of the bearing tube and then played around with the tightness of the clamp - I was able to vary the lossiness of the I beam from rigid to virtually floating. Then I settled the point that gave the most natural bass soundwise with air around it.
Re the magnetic dampening, I used a small cupboard door magnet and simply placed it on the turntable plinth with a packer to get the magnet as close to the bearing tube ( the moving one ) without touching it. This magnetic dampening is used by Dynavector on their tonearms where a curved horizontal metal near the counterweight moves through 2 magnets above and below it as the tonearm transverses the record. |
Ketchup, I used the ET2 before the magnesium arm wand came out. The arm was smooth and gumetal grey under the shrinkwrap. !st I removed the heatshrink, more agile sound, then I removed the foam inside the arm tube - lighter sound but much more transparent.
For the cartridge mount I carefully prised open the end of the arm, enough to get long nosed pliers onto the soft insert and pulled it out. Then I got a thin piece of carbin fibre, cut to size, then inserted it into arm with araldite and clamped the headshell until dry.
I never compared this to the magnesium arm.
Cheers |
Apbiii - Martin Colloms did some testing of energy transmission in the ET2 years ago. He measured the resonances in the arm tube and then in the arm after the air bearing. The conclusions were that the unwanted energy transmitted went straight through the air bearing and out the other end relatively unimpeded.
This is the old chestnut - do you kill unwanted energy by overdampening, or by having a drain path to ground ( the plinth ).
The main issue with overdampening is that soft materials eg rubber, will store energy and then release it "out of time" with the music, thus smearing the sound.
People will have their own preferences, do you want to hear everything, quick, coherent, lively if a little coloured, or do you like a nice smooth inoffensive sound if lacking a little speed, detail and coherence. |
From the arm tube to the plinth and the energy resonances measured were very close, ie transmission rate was very high. |
Although I'm no longer using the ET2 at the moment, one record I found that is readily attainable is Joe Jackson's Jumping Jive. On the track titled "Five guys named Moe" there is a part where Moe is repeated 5 times. With the ET2 you can clearly hear each utterance and the position, starts front slightly right of centre and each "moe" is behind and to the left of each preceding one. The ET2 is the only arm I have found that captures this positioning in space so clearly. |
Hi all,
I'm a big fan pof the ET2 modded even though I dont run it, went to unipivot primarily to get rid of pumps etc. You have to read the thread in WBF, I simply cannot believe the sheer ignorance of many of the contributors, the worst being Astor and Lavigne. Not much hope for credible audio reviews from these folk. These guys are idiots and I doubt much of their gear is set up correctly from their lack of understanding of basic physics.
http://www.whatsbestforum.com/showthread.php?5653-Linear-tracking-Turntables!
PS If you have low tolerance levels dont bother reading it. Make sure you have your sense of humour on board. |
Ct0517,
What interested me, or should I say piqued me, was the comments on lack of bass with ET2. I have run and listened to extensively the ET2 on the following TT's - Sota/Sota Star/Roksan/Townsend/Goldmund Studio/Technics SP10mk3/Final Audio. I was clearly getting more bass extension with some decks than others with the same cartridge/system, which tells me that the ET2 was not the limiting factor in bass extension. With some of the TT's the bass notes would "flat spot", in other words organ and double bass notes rather than go down further down the scale, the lowest notes would play incorrectly. |
Now here is a poser for all you guys -
An engineer/mathematician friend of mine suggested many years ago that if you run a tangential tracking tonearm and set the stylus exactly on the tangent, then the stylus has no reference as it has no lateral forces acting upon it and hence it is unstable. ( for those of you old enough think old fashioned cars with kingpins and wobbly steering when centered ).
His proposal was that if you run a tangential tracking arm then you should run a tiny amount of overhang and tracking angle on the cartridge.
Thoughts anyone...
|
|
Frogman - yes. Ed Thigpen's response at the time was "he's probably right".
Dgarretson, I use to check the level on my ET2 by balancing it to 0 with an additional counterweight and checking that when nudged the arm would travel freely and the same distance in both directions from centre. This as well as a level on top of the tube. Possibly a string bias weight type of weight pulling on the end of the armtube may be "gentler" than tilting the arm in your instance ??. |
Ct0517 - I would not run an ET downhill, but I get the overhang argument.
NOW HERE IS ANOTHER POSER to ponder :
With a pivoted arm we have an overhang. The pivot arm/stylus tip moves in an arc, which means that for every 1.8 seconds ( 1 rotation ) the stylus tip has actually moved slightly forward with each rotation.
Put another way if you put the stylus tip in the first groove, and draw a tangent to the spindle centre, then with each rotation the stylus tip will move further ahead from that tangent.
This means that to achieve the correct playback speed, with a pivoted arm, then the TT needs to speed up with each rotation.
This means that the only playback system that is accurate in terms of speed is in fact a linear tracker.
Now...thoughts... |
Bear in mind that you are not comparing a Dynavector 17D to an Acutex 420.
You are comparing a "Dynavector 17D plus Bob's Cinemag 3440 MC transformer" to an Acutex 420. |
Frogman - that was one point I was going to mention that has not been covered, the tightening of the 4 bolts on the manifold. I tried one bolt tighter than the rest to get a single point ground effect, but ultimately came to the same conclusion as you, evenly and not too tight.
Re the cabling, my ultimate set up had the armwire running straight from the wand to a teflon block on the side of the tt plinth midway along the arm travel, ie centered. But I also turned my preamp sideways and backed it up to the deck so I only needed 6" of cable from tt to pre. I simply soldered the arm wire straight into the phono cable. The whole loom was probably not much more than 14". For some customers I would install phono inputs on the side of the preamp, if the phono was situated on the left, so they could put the preamp next to the tt and run super short looms. In my own instance 6" of raw MIT cable beats 1m of MIT Oracle ( and probably any other phono cable out there ) easily in this application. The best wire I found was a silk ofc litz, preferred to stock, Vdh silver & cardas.
|
Another tip from downunder - I found plugging the pumps into isolation transformers rather than directly into the mains smoothed the sound out quite a lot even with dual pumps/surge tank etc. |
Last one I saw sold for US$2500 on Ebay only a few months ago, cant remember what arm it had on it. So the thing is worth about $5-6k, plus some premium for condition. Based on the sellers perception of value maybe I should offer him my Final Audio for $20k plus the Nakamichi. I think the CT would be better. |
Ct0517
Fyi the Final Audio TT uses a 35mm thick slab of superplastic zinc ( SPZ ) for the "plinth" - weight of plinth exclusive of platter/bearing/armpod/arm is approx 40kg. The inverted bearing and armpod are bolted directly to this slab. Info is here :
http://books.google.co.nz/books?id=ohQdU5ggcOIC&pg=PA143&lpg=PA143&dq=superplastic+zinc+(SPZ)&source=bl&ots=uDqm8e0JsG&sig=oPdsNcyBUypOB6D9VWdrx_vFdgQ&hl=en#v=onepage&q=superplastic%20zinc%20(SPZ)&f=false
The base is tight and quick.
My experience is that slate does ring. A friend of mine is now working on a ultra lightweight composite powdered ceramic sandwhich plinth for the Garrard 301 to try a "non stored energy" approach having discarded slate/panzerholz etc. |
Slaw -
With regard to the aluminium plate/acrylic. I would not run the plate, it's added resonance. I have moved away from metal spikes, and if I use them I radius the tip so it is not a sharp point. I say radius, as in rounded, NOT flat. The idea is a small radius tip sitting in a larger radius hole as per most unipivot bearings. My suggestion would be to radius the tip of the grubs screws and then you should be able to couple directly to the acrylic without damaging the surface. In an ideal world the acrylic would have a dimple in it for the radius tip to sit in. |
Hi Slaw - here are a few suggestions for you to consider -
Wiring loom - I would untwist the wire between the arm and plinth to reduce resistance. I would also place the anchor point for the cable on the plinth at the midway point of travel, not the end.
I do not subscribe to separate pods for arms, the arm must be rigidly referenced to the bearing point. Your use of rollerballs in the TT with a separate pod would be a disaster in my view.
Use your woodwork skills on the speakers - pulling the crossovers out of the box, even without changing any components, will yield a significant improvement in resolution and lower noise floor. |
Ct0517 - I last used my ET2 with a Garrot modified Denon 103. Also used Koetsu Black & Shure V15VMR.
As far as springs go, I really didn't use the spring effect at all. I found that even with low compliance cartridges, when you reduced the horizontal compliance, the bottom end tightened up, but became more and more out of time with the music. TT at the time was a heavily modded Sota Star. The solution I ended up with was leaving the end cap only partially done up, and used teflon wedges partially inserted either side of the "spring" to a point where the initial movement had almost no restriction whatsoever, but the range was limited and ultimately tempered by the teflon. This with the magnetic dampening explained in my earlier post yielded the best results with both high and low compliance cartridges. I guess what I ended up with was virtually a decoupled counterweight assembly with a very gentle progressive dampening via the teflon wedges.
|
|
Frogman -
I got considerably more transparency and even less grain when I removed the inner foam and stripped off the heatshrink from the aluminium arm tube with both low compliance ( Denon 103 Garrott ) and high compliance ( Shure V15VMR ) cartridges.
Also I suggested implementing electromagnetic dampening of lateral movement by using fridge magnets early in this post - disappointingly for me, only ct0517 has tried it - a $5 tweak that stabilises the cartridges so much, you get increased output and have to turn the volume down. The dampening increases proportionally with lateral arm movement speed.
By the way magnesium has a lower Youngs Modulus than aluminium, which means it is much softer and less rigid ceteris parabus.
If you want to go one step further, you can open up the cartridge end of the wand ( the aluminium is very thin ), pull out the soft teflon insert, and replace it with a piece of carbon fiber. You can use superglue and clamp it up with a decent vice. This gives you a much stiffer headshell. |
Frogman - the order I went through was -
1st removed inner foam - listening test
2nd removed heatshrink - listening test
3rd modified head shell - listening test
4th added electrodampening - listening test
My personal view on fluid dampening is that it slugs/smears the sound, as does spongy dampening such as foam/heatshrink.
Your experience with the Spectral MCR mirrors mine.
I would suggest you disengage the dampening trough first - so you can hear the other changes more clearly.
Good luck. |
Chris, hi there,
Thats exactly where I ended up with the Shure V15 - 1 lead weight far far out.
I think with the electrodampening of the lateral tube motion and decoupling of the beam in place, even low compliance cartridges benefit from least weight furtherest out approach. |
Thanks Chris - I would take up your offer, but alas I cant get the ET back yet. I am having to play the long game on this one. I would be happy to throw it on the Fidelity Research FR64S/Dynavector DV501/Naim Aro if you are interested. |
Nandric - I'm an honorary member of the ET2 club having owned one for many years since the 80's. Unfortunately in a moment of madness I gave it to a friend who bought my old Roksan TT. It will come back eventually. |
Nandric - do you have a ranking for your MC's at this stage. Am very interested to hear what you think of the Magic Diamond. The Kiseki Silver Spot I know well so if you do a comparison to that then I can work it out from there. |
Hi Chris/Grant
Yes I used 2 pumps running into a 20 litre surge tank. On the pumps I used, reversing phase & neutral at the transformer inside reversed the phase on one of the pumps. In NZ you must not reverse phase and neutral at the power cord because the mains fuse must be in the phase line. |
You've just reminded me - I got a big improvement when I put an isolation transformer between the mains and the pumps. Much smoother sound. |
Richardkrebs Re: your ET2 mods. Here are a few points for you to consider. I have a view on linear arms in that the rules for pivoted arms and effective horizontal mass do not apply. In fact I have added a lead slug inside the bearing spindle 25 mm long…
This combined with the fixed counterweight means that the arm is HEAVY in the horizontal plane. This view is indeed strange. Many records are off centre. By increasing the horizontal mass of the arm significantly, when you play an eccentric record the increased resistance to motion from the additional mass will result in increased cantilever flex. On eccentric records your approach will result in phase anomalies during play back, increased record wear and probably cartridge damage in the long term. My ET2 has been lightened, no internal dampening, no external tube dampening, decoupled counterweight and have had no issues tracking low compliance cartridges, achieving extended bottom end with speed, articulation and accurate timbre. Magnetic dampening controls lateral motion on eccentric records. The arm is optimized for low compliance carts. As you can see, just, from one of the pics Ketchup found, it has a fixed counterweight. I have found the opposite. Using various Koetsu’s and a Denon 103 Garrott I found that there is an optimum decoupling point. Eliminating the decoupling resulted in more “apparent” bass but with less speed, articulation and timbre. In my decoupling methodology I used teflon pads either side of the spring with the end cap quite loose. This gave a soft lossy quality to the motion as opposed to springy. On the magnetic dampening front the negative I heard was possibly caused by the induced circulating currents interfering with the cartridge output I could not hear any distortions of this nature with the magnets located on the opposite side of the manifold from the cartridge wand and using copper litz arm wiring that exited before the gooseneck and straight into the phono 12” away. Cartridge leads are single strand silver lightly twisted at about one turn per 8 mm. Continuous to the preamp Highly prone to rf, might explain your perceived issues with magnetic dampening. Have removed the Teflon in the head shell and replaced with a square of 1/2 mm thick lead and super glued in place. With low compliance cartridges, there is significant energy generated for the arm to deal with. This energy needs to be wicked away from the cartridge and sunk to ground. To maximize this energy flow away from the cartridge materials should be used that that successively increase propagation speed heading towards ground. This encourages the energy flow away and minimizes reflection of energy back towards the cartridge. Inserting lead into the head shell creates an energy reservoir that will sink energy, but due to the softness of the lead some will be released back into the cartridge out of time with the music. The same argument applies to the use of a lead slug in the bearing tube. This causes smearing and loss of detail. I would not recommend the use of lead. One other question I have on your SP10mk3. You mentioned you are using an acrylic/lead/acrylic plinth. It appears from the photos that you have bolted the motor to the bottom piece of acrylic and the ET2 to the upper piece of acrylic, with the lead layer in between. If so this would compromise the loop rigidity between cartridge/arm/platter required for accurate playback. |
Hi Chris - yes I agree with Thigpens comments, but I think Richardkrebs high mass approach throws away the advantage of the ET2 over other tangential arms, that is the light horizontal mass. The ET2 is less than 25gm compared to the 80g of the Terminator. The effective horizontal mass of the ET2 is even lower with a decoupled counterweight. The other problem with adding mass to the ET2 is that not all low compliance cartridges are created equal, as the compliance in the horizontal plane cannot be assumed to be the same. For example the Denon 103 is far more rigid in the horizontal mode than the Koetsu even though they are similar compliance vertically. |
|
Chris/Richard As per my earlier post, both an oil trough and a magnet impose a resistance to lateral movement as seen by the cantilever. They behave much like weight in the lateral plane. I have simply used weight alone. This is incorrect. This is like comparing apples, oranges and pears. Magnetic dampening will vary with the speed of horizontal motion whereas the added mass approach is simply increasing static inertia considerably. The resultant behavior from an additional horizontal force will be quite different. Same for fluid dampening. In terms of sound - with magnetic dampening I have gotten increased cartridge output, which indicates that the cartridge is losing less energy due to micro vibrations being damped. By contrast with all fluid dampening I hear a loss of speed, focus and detail. Dynavector also concur with this view in their discussion of their tonearm design. Despite the high horizontal mass they use eddy current dampening to reduce micro vibrations. In my view the ET2 is the best arm I've used. I changed to a Naim Aro due to problems with a sprung floor and growing tired of pumps, tanks and airhoses running through the house. The ET2 is out on loan, but at some stage it will come back. In engineering terms a unipivot is the most rigid bearing you can get. I chose the Aro because compared to the Graham of the day it had no arm tube dampening, the Graham arm tube was full of crap, and the bearing was the correct way up for energy dissipation to ground ( the Graham had what I call an upside down bearing, point up ). The sound of the Naim Aro is quick, lucid through the mids, excellent soundstage and very musical. The downside is that I believe it has a very narrow operating window in terms of cartridge compliance and mass. The Dynavector Nova 13D sounds excellent as does a Denon 103D. The Koetsu Black sounds awful, unstable in the bottom end. I recently purchased an FR64S to try with my Ikeda Kiwame - this arm is one of the best pivoted arms I have used and due to the detachable headshell I am currently running this so that I can play around with all my cartirdges - Ikeda Kiwame, Dynavector Nova 13D ( freshly rebuilt from the ground up by Dynavector Japan ), Koetsu Black and Denon 103D. No pivoted arm in my experience can match the transparency and presentation of the soundstage as well as the ET2 though. Furthermore as you will be aware, there is plenty of bottom end depth and speed if set up properly, despite reports to the contrary. |
Richardkrebs/Chris :
Magnetic Dampening vs Mass.
I have been away on business and my responses have been brief. I can now expand on my previous comments.
With a lower mass the arm will move more rapidly initially to align with the eccentricity of the record, minimising cantilever flex.
The magnetic dampening only commences its action once the arm starts moving, and is proportional to the rate of movement. I should point out that the dampening is created by eddy currents which are only generated when the arm moves relative to the magnet.
By contrast, adding mass means the arm will not move until the driving force from the eccentricity is enough to overcome the higher inertia. This increased resistance to movement from the added mass means that the cartridge cantilever is forced to deflect to keep the stylus in the groove. This defeats the purpose and advantage of an air bearing tonearm - the uninhibited degree of freedom to accurately track the groove.
This higher mass is not dampening, it is increased inertia - a resistance to movement.
Magnetic dampening is dampening the arm motion once the arm has commenced movement.
I'll restate this :
Magnetic dampening allows the cartridge to move to the correct position in a damped fashion.
High mass means the arm wont initially move, inducing the cantilever to bend.
Any excessive cantilever deflection in a moving coil will result in phase anomalies as the coils attached to the cantilever are driven into a position where the response becomes non linear.
Furthermore, with the higher mass, once the arm starts moving, the lateral movement is undamped. Cartridge overshoot and more cantilever flex is inevitable.
With magnetic dampening the lateral movement of the arm is always damped when moving. |
John47 - you misunderstand how it works. It is not magnetism that provides the dampening. It is the eddy currents created when the arm moves across the magnet. Read this http://en.wikipedia.org/wiki/Eddy_currentEddy currents (also called Foucault currents[1]) are electric currents induced within conductors by a changing magnetic field in the conductor. These circulating eddies of current have inductance and thus induce magnetic fields. These fields can cause repulsive, attractive,[2] propulsion, drag and heating effects. |
Frogman - I used a cupboard door magnet. It had a pair of magnetic plates implanted edge on. You see 2 parallel edges exposed in a plastic case. I placed these on the plinth, under the bearing tube with the edges in line with the bearing tube, next to the manifold, on the other side of the manifold from the cartridge. Like this ( looking down the bearing tube )
O bearing tube
!! magnet(s)
-- plinth
Note that my modified arm cable loom exits the arm wand in front of the bearing tube, it does not pass though the bearing tube. |
Ct0517 - fyi
Magnets can be a little eccentric. On Richardkrebs deck they may prefer the wand end because they get a better view of the cantilever doing her one legged tantric yoga exercises. |
Richardkrebs -
I'm a little disappointed you dont think outside the box, or in this case arm.
What about running 2 ET bearings in a T bar configuration, armtube in the middle.
You like magnetic dampening but worry about the eddy current. Try standing on your head and thinking upside down. You dont have to use the bearing tube.
Why not use a magnet as a counterweight and an aluminium bar mounted on the plinth. Why not go the whole hog and put an accelerometer on the bearing housing, that way you can measure the resonance and employ electromagnetic dampening driven from a feedback loop and active servos to dial out the exact resonance.
What I do know is that added mass will have altered the dynamic stiffness of the bearing and the fundamental resonance. It will increase the instability in that air bearing. You are running 12psi - this is on the lower end of what most are running ET's. With the added mass you are increasing the very instability you are complaining about with the magnets.
Have you measured the dynamic stiffness and fundamental resonance after adding mass ?
Have you calculated how much you need to increase the pressure by to provide the same level of rigidity in the bearing as the standard arm ?
Have you measured the impact in the high frequencies of being able to achieve the same level of rigidity with less mass ?
When it comes to resonance mass is your enemy. Do you put lead in your gumboots for a smoother ride when you go tramping ?
Perhaps you should resign yourself and go to a unipivot. An air bearing will never be as rigid as a unipivot - you are losing so much of the leading edge of notes. That would solve all your anxieties and give you a whole new set of issues to fret upon.
PS The tantric yoga is no joke - stand on one leg, put the other to your ear, and you may hear a little more bottom end. |
Hi Chris, thanks for the complement. Yes I do try to be flexible. I am contemplating a post grad course in pseudo science at the Massachusetts Institute of Technology. This may help me comprehend some of the recent posts on the forum. |
Richardkrebs Thou doth protest too much, methinks About what exactly. You raised the issue of bearing stability and the placement of magnets. The mass you have added to the bearing tube destabilizes the air bearing. My question to you as to whether you have measured the reduction in dynamic stiffness in the air bearing as a consequence of your modification and how you intend to remedy this remains unanswered. You encourage people to try your modifications. These modifications could damage expensive cartridges and records. Are you inferring that these concerns about your modifications should not be raised. |
Yeah I got all that the first time. We'll never agree on the added mass approach. But anyone trying it should check their cantilever deflection on eccentric records to ensure the cartridge can cope.
I'm sceptical on the degree of movement in the bearing, but if there is movement then stylus drag will pull the bearing tube forward on that side of the air manifold.
IMPORTANT NOTE for Frogman/Chris
What folk need to know is that if you use 2 magnets either side of the tube ( forming an eddy current clamp ), the dampening will increase disproportionately. I have seen controlled studies where dampening of unwanted energy has reduced by 80+% with 2 magnets either side of a beam instead of 1. You place the magnets S-N Beam N-S
Your ultimate solution if you want maximum dampening would be 4 magnets, 2 pairs either side of the manifold in the "S-N Beam N-S configuration".
I could argue that if you use 2 magnets in a clamp arrangement, you might be better off clamping the counterweight end and letting the stylus drag of the wand pull that end of the bearing tube against the bearing wall naturally. That way you dont have conflicting forces created by the eddy currents and stylus drag fighting on the wand side.
When positioning magnets for eddy current dampening, closer is not always better, the magnetism has nodes that vary up and down with distance. |
Chris - since I am not running the ET at present, would be good if you could test the eddy current clamp I describe in the above post, using 2 magnets clamping the tube at one point in "S-N Beam N-S" configuration. |
|
Chris - Thanks for the feedback. I always thought shagging around with the system was housework. Out of interest do you run your Verdier with or without the ball inserted ? |
Richardkrebs, I have finished testing Dover's mag configuration on my modified ET2 For the record you have NOT tested my ( Dover's ) configuration at all. You have only tested magnetic dampening in the context of your own reconfigured version of the ET2. Your added lead mass has pushed the operating parameters of your ET2 outside of the original design. Your ET2 is set up completely differently to mine in that : You have rigidly coupled the counterweight to the arm. You have added lead mass to your bearing tube. You have added lead mass to the headshell. You have increased the horizontal mass significantly over the standard arm. The configuration I use is: Decoupled counterweight in the horizontal mode ( spring bypassed ) Lightened tonearm Minimal magnetic dampening The level of actual magnetic dampening I use is as follows : Shure V15VMR - 1 cupboard door magnet under the bearing tube at counterweight end Koetsu Black - 1 cupboard door magnet as above Madrigal Carnegie Model One - 1 cupboard door magnet as above Denon 103 Garrott ( Aluminium/Boron hybrid cantilever/Weinz Parabolic diamond ) - none Yet again, and you seem to do this with monotonous regularity, you misrepresent statements and arguments in order to justify your own point of view. 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. On their web site it does not say what these weights are made out of, but brass or stainless steel would be reasonable asumptions. Extra weight like this would dwarf the 30 or so grams I have added to my ET. Your argument is wrong. The Morch arm is a pivoted tonearm. The ET2 is an airbearing tangential arm. The Morch applies its mass at the rotational pivot point. You have added lead mass to your ET2 at 3 points - the headshell, the bearing tube and the counterweight. One needs to understand the physics as it applies to Linear Dynamics versus Rotational Dynamics. The added mass under these different conditions will have quantitatively different outcomes. You don't appear to have considered this at all. Furthermore, the Morch website confirms my earlier statement that added mass, magnetic dampening and fluid dampening are not the same yet you contend that they are. Morch state on their website that mass increases inertia and has no dampening properties as I explained to you earlier. Morch use silicon fluid to dampen the motion in addition the added mass weights, again, which only increase inertia. Your earlier contention that added lead mass is the same as fluid or magnetic dampening is incorrect. Again I caution readers that adding lead mass in the manner advocated by Richardkrebs could potentially lead to cartridge and record damage when playing most records which are eccentric. Why ? Because the added lead mass is loading up the cantilever. |
Richardkrebs para 1 - not obvious to everyone. You are testing the effect of magnetic damping with an ET2 with rigid counterweight and high mass. Chris has been testing magnetic damping with partially decoupled counterweight and no added mass as has Frogman. I have not said that mass, mag damping and fluid damping are the same other than that they all resist motion and that this resistance increass with frequency. This simplistic view fails to differentiate between inertia and damping of motion. During the course of this debate over the last few weeks you dont seem to comprehend the difference between inertia and damping of motion. Inertia is the resistance to a change in its state of motion or rest. When you add lead to your ET tonearm you increase inertia. By increasing inertia the cantilever will flex more on eccentric records. Damping is the retardation of motion once the movement has commenced. This means the cartridge can move straight away with an eccentric record, which results in minimal flex in the cantilever, and less distortion, but eddy currents generated by the motion of the arm relative to the magnet retards the oscillation of the arm and cartridge. Adding lead mass creates higher inertia but does NOT retard motion. Magnetic dampening has lower inertia and dampens motion. I repeat again that the lead mass that you have added puts more load on the cantilever when the arm tries to move to accommodate an eccentric record. Furthermore, with the higher mass of the added lead, when the arm moves there is more momentum, there is no control over this mass, and there is no damping of motion to minimize overshoot as the arm tries to correct. As viewed by the cantilever this is no different to me adding mass in the linear plane to the ET. Again - a very simplistic view of the world. Pivoted arms have tracking error and offset angle. The physics is quite different to that of a linear arm. Adding mass but Morch with their flywheel do not appear to have reached that point nor have I with my arm. This is an assumption and speculative. I could just as easily surmise that the Morch arm is so thin and lacking in structural integrity that it needs added mass and fluid dampening to control energy and resonances in the arm generated by a good moving coil cartridge. Conventional mathematics says that adding mass to a flywheel, not only increases inertia, but it is harder to slow down. You are making the problem of navigating an eccentric record bigger than it needs to be. |
Hi Chris - Yes I have a good memory. When we first imported a pile of ET2's we had in the shop an ET1. There was a big debate at the time that the ET2 had less bottom end than the ET1. The ET1 has a fixed counterweight. My business partner preferred the counterweight bolted up as per the ET1, but I found that gave a one note bottom end, lacking speed and articulation.
I experimented with the counterweight coupling and other ET2 mods quite extensively not only with a variety of TT's including Sota Star Vacuum, Townsend Rock, Roksan, Oracle and Final Audio TT, but also a variety of speakers including Martin Logan CLS, Apogees, Proac EBS, Proac Tablettes, Duntech's, vintage Tannoy Monitor Golds and many others - over the last 30 years.
Also have run the ET2 specifically with a wide variety of cartridges including Madrigal Carnegie, various Koetsu's, Van den hul Grashopper, Shinnon Red, Sumiko Talismans/Virtuoso's, Shure V15VMR, Denon 103 Garrott, Benz Reference and many others I've long forgotten.
I have also seen enough off centre cantilevers to last a lifetime from the misapplication of both tangential and pivoted arms.
|
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.
|
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. |
Chris, the good thing is, if we have a bad day over here we can fly over to your place and start the day again ... |
Richardkrebs I have queries regarding your claims re the Kuzma air bearing tonearm. This appears to be unique in using a porous material rather than multiple drilled holes like the ET. This is not correct. The ET has a captured air bearing with a continuous air gap between bearing spindle and manifold. We went on to talk about potential problems with cantiliver flex. His response was the resonant frequency due to the combination of a typical low compliance cartridge and horizontal effective mass was in the region of 2.5 -3.5 hz.(this has been published by them elsewhere), this is well above the 0.55 or 0.75 hz for 33 or 45 rpm eccentric records. Therefore the cartridge does not "see" this movement. This defies basic physics. Any lateral force on the stylus forces the cantilever to flex laterally, until the resistance of the cantilever to movement meets or exceeds that of the arm, at which point the arm must follow. More mass in the arm = more inertia in the arm = more flex in the cantilever. This Video was posted by them to allay fears of cartridge damage due to high horizontal mass.
This arm is amongst the best currently available. It has a large differential between its vert and horizontal effective mass figures and does not appear to be a cartridge killer. The video does not show the cantilever. Proof of the above assertions is not demonstrated. As regards the best available, what other arms have you auditioned to draw this conclusion. If you are talking air bearing arms - where have you considered the dynamic stiffness of the air bearing. Although the Kuzma runs 60psi into porous tube versus the ET2 at 19psi into captured air bearing, the psi alone does not determine the dynamic stiffness. Some other factors you need to consider are : The hole sizes The flow of air The surface area of the bearing etc The ET2 also has a wider manifold. If we assume for arguments sake the air bearings are of equal dynamic stiffness, the ET2 will be inherently more stable than the Kuzma. He assures me that there is no problem with the cantilever under these extreme circumstances. This is an inadequate response. To support your contention that adding mass has no deleterious effect, which cartridge designers have you sought an opinion as to loading up the cantilever in the manner you continue to advocate in this thread ? Bruce Thigpen's patents clearly outline the benefits of the decoupled counterweight and lower mass. |
Richardkrebs Referring to your last post 03-12-13: responding to Dover. At frequencies below resonance the cantilever is free to push the mass of the arm sideways. This does not defy physics, it is physics. Correct In other words the cartridge suspension is stiff enough to accelerate the arm mass sideways. . That is an assumption that will depend on the compliance of the cartridge. If the compliance is low enough then possibly, but before the acceleration commences the cantilever will flex. You seem to be unaware that cantilevers are mounted in a rubber elastomer that is not rigid. Think of a tension spring with a weight suspended at one end. This combination will have a resonant frequency. If you hold the spring end opposite to the weight and move it up and down at a frequency below resonance the weight will move up and down in sync with your movement. The spring will NOT stretch as a result of this movememt. . A curious analogy, yet again, you compare apples and oranges. Your analogy compares 1. Holding the end of a spring with a fixed weight on the other end to 2. The stylus point sitting in a groove, not held, at the end of a cantilevered beam, at the other end of which is a rubber suspension ( not a spring ), and the other side of the suspension has a mass loading that is constrained at 90 degrees by the rigid air bearing some 6 inches away. Your analogy is a triumph of the imagination to consider these two scenarios in the same manner. Your discourse on resonant frequency is irrelevant. Quite frankly I cant be bothered doing the maths, but I defy anyone to show me a cantilever that does not flex when playing an eccentric record. This does indeed defy physics unless you have a cantilever that has zero compliance. No, the video does not show the cantilever, that is why I asked him if it was a problem. If you agree the video does not show the cantilever then why do you repeat the following statement that is misleading? I repeat the video is shown specifically to allay fears of problems due to high horizontal mass. . I assume from your lack of response that you have not sought any advice on this matter from any cartridge designers. I would have thought this was the first port of call for a thorough and complete understanding of the problems of navigating eccentric records. |
Thekong Thanks for sharing your experience. I agree with Fremer. Thigpen does appear to hold patents on the decoupled counterweight. Whereas Walker uses a fixed counterweight at 45psi in the Proscenium, Richardkrebs advocates using a fixed counterweight, adding additional lead weights and running a relatively low pressure of only 12psi in his ET2. In my view his modifications increase inertia and increase the loading on the cantilever suspension when side forces from eccentric records are presented to the stylus. He employs no dampening to control this increased mass. Once it moves there is more induced cantilever flex from overshoot. This is way outside Bruce Thigpens original design concept of low mass and decoupled counterweight and should in no way be construed to be an ET2. There is always the risk of cartridge and or record damage with Richardkrebs added mass-low pressure approach. Richardkrebs advice in a previous post for those concerned about possible cartridge and record damage was, quote People are free to try, it is entirely their choice. Install an alternate cheap cartridge, play a record you don't like, if you are that worried about damage to same. This advice is probably about the only thing that Richardkrebs and I could agree on. |
