Dover - I always thought shagging around with the system was housework Dover – What is your definition of shagging. If you mean ‘experimenting’, its a release for me along with a couple other hobbies from staring at a screen for 30+ years in IT. The problem is when I get on to something I disappear. I promised my wife yesterday if she let me play with some magnets I would watch the Oscars with her. Re: The Oscars - She thinks I am like the guy in Silver Linings. I saw it a month ago – some parts hit home. I tell her my meds are the music, running ...and a little red wine. Out of interest do you run your Verdier with or without the ball inserted? My opinion on the setup ball was expressed here. setup ball |
Good work, Chris. I look forward to trying the magnetic clamp arrangement, and will post my impressions. So far, we are hearing similar effects with the two different arrangements that we have used. I do get the strong feeling that my current arrangement does not fully exploit the potential of this tweak. Well, I guess that loose floor molding is going to have to wait; darn! ;-) |
Chris,
When you had your three magnets in a row, did you notice any difference in sound as a record side progressed? |
Chris
Yes happy to try this mag dampening variation. One more time around the block will do no harm.
It will be awhile though as I am still dialing in my remodeled room and new shelter cart. The system is a bit of a moving target at the mo.
Thanks |
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 ? |
Dover
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. Ok wanted to get this out so excuse any errors. here is the temporary setup pic (lower one) showing the same pole magnetsproviding eddy currents from both sides of the spindle. The Blue tac marks the north poles of the magnets. Will be making the magnet platform out of something else. Here is what I did today instead of house chores. Went and picked up a package of the magnets you see in the pic. There are 8 in a pack for $3.00. Thin rectangular pieces. I took two – put a string between them – let the opposite poles hold the string. I then let it hang very gently so one of the sides pointed north. Either it remains as north or it started turning to get to north. I marked the north poles with the blue tack you can see. I guess you can see I like this blue tack stuff. I cut a temporary piece of wood high enough to just clear the spindle and placed the two magnetic pieces on wood. The magnets could fit just below the spindle right now if I slid them across. With this setup then could be raised and placed on either side of the spindle too. Dover
When positioning magnets for eddy current dampening, closer is not always better, the magnetism has nodes that vary up and down with distance. The distance that can be seen between them in the pic; is the minimal amount allowed in this setup. Any closer and the magnet pieces with the same pole magnetic repulsion start pushing each other off the wood. Sort of like my twins - sorry had to throw that in. They are just resting on the wood. This is how my TT works – magnetic repulsion - that produces levitation. So all of this feels like I am playing on home turf. Impressions - To describe what I hear would be just another opinion and I am no good at describing sound. Plus all our setups are different. So lets use a car analogy again. You can buy cars that have buttons that give you sport – normal – and cushy suspensions. You push the button to select the ride type based on road conditions. The different LP/Records being the different roads here. What if a car was made that did the switching for you automatically. If the road got worse or changed to gravel, the suspension changes on its own and cushions it. The resulting ride would be quieter and smoother and you can hear yourself talking with the other passengers better. Thats more of the sense I am getting with this setup. Records are quieter, highs more refined similar to past magnet damping, but now it seems more consistent/stable. This is only based on 6 or 7 familiar lps. All ET2 tonearms owners should try this. If you have some records that are more off center, sound more splashy to you then others - try them first. Once I have settled into the sound I will make a pillar for the other side to hold two similar magnets at the start of the manifold and listen again. Frogman looking forward to your impressions as well as others that try it. Richard – I know you tried many variations of magnetic damping. Did you try this same pole magnet clamping style ? Early on but am not able to detect any eccentricity or excitement in the spindle yet. Music seems to be very controlled, stable. ET 2.5 spindle 19 psi. Thanks for the suggestion Dover. Cheers |
Playing with magnets. From yesterday the pic shows two magnet setups The top setup is superior. Three on top of one another not alongside each other closer to the spindle. Dover will try the Eddy magnetic clamp later today. It is just 9am here Sunday right now. If you look at the bottom pic you can see I do not have alot of space to work with for two magnets either side of spindle. I will clamp a small platform there with some blue tac today to allow me to put two magnets up closer to the spindle and on either side of it. Will pick up some square magnets today to give the S-N Beam N-S ------O---------- Beam/Spindle S || N--N || S---- Magnets Being an IT guy I hope you are impressed with my illustration. I took a cue from you. Cheers |
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. |
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. |
Dover
Adding mass to the spindle helps to stabilize it.
To repeat, for a given resonant system, extra mass lowers the resonant frequency and reduces the amplitude of this resonance. This is F=ma again. Force the same, Mass up, means acceleration must go down.
I agree that adding too much mass is potentially a problem. Where we disagree is at what point this extra mass becomes a problem. Pivoted arms, as seen by the cantilever, have high effective mass due to the head shell offset. Yet nobody seems to worry about this. I would also suggest that anti skate is significantly more dileterious to the cartridges health.
Placement of magnets..... Below the bearings natural resonant frequency, it is effectively loose, above it is nearly rigid.
So the thought experiment is where is it best to place a restriction to movement which creates a pivot point in order to minimize unwanted movement of the wand. If the mag is placed wand end, the bearing clearance allows wand movement at frequencies below natural resonance but not as much as when the mag is placed at the counterweight end. This is not a bearing stability issue, it is just optimizing the bearing geometery. Like I said this the same principle employed with inverted bearings in TTs. |
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. |
Ketchup
Yes agree, I would use a rotary table which we now have. But is it really a big deal if you don't change carts often. Critical in any design would be rigidity once set. |
"I am contemplating a post grad course in pseudo science"
So you've already graduated/excelled in pseudo science. |
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. |
I need to do the math, but I bet the change in overhang is pretty small with the typical VTA adjustment.
If I were to build one, I would machine the arc with a rotary table and a milling machine (because I don't have cnc capabilities). |
Ketchup
I should have added. The lack of the arc feature is not a big deal for me since I don't change carts often. Others who do, would find this feature helpful. |
Ketchup
No it doesn't incorporate the arc on the VTA adjustment
I didn't have the machining technology to do this back then
I tune in the approx VTA then check alignment. Then final fine adjustment of VTA and recheck alignment again.
The new arm will likely have the arc feature. |
Richard,
I know we're talking magnets right now, but I have a question about your design. You did away with the original arc block which enables overhang to remain constant while VTA/SRA is adjusted. Does your design incorporate such a feature? |
Chris
Yes various magnets tried in..,...completely original ET2 , ET2 with fixed counterweight. My manifold with and without lead slug.
All iterations also tried at wand and counterweight end.
( not both ends simultaneously )
All tests done at 12 psi
Dover, for a given resonant system, all else being equal, addition of mass will lower the resonant frequency and reduce the amplitude of this resonance.
I had a dual manifold arm on the drawing board well before I rebuilt the ET. Feel free to check with RW for confirmation.
I currently have a pseudo active dampening/mass system in the early stages of development. It doesn't use mags or conventional feedback and IMO it is elegant in its simplicity. If it works it would eliminate the lead weight.
And to miss quote the Bard just a little......
Thou doth protest too much, methinks |
Frogman - I have been thinking about that too. Since that pic I have them on top of one another in one pillar. Will try that out. My TT setup does not allow for magnets on both sides as the arm is on a pillar. Look forward to your observations with them on both sides.
Richard, Dover, others - based on your experience if only using the magnets on the counterweight side of the manifold - can u tell me what the most effective arrangement was. I will try various arrangement as well as one larger magnet instead of few smaller ones. |
Chris, after looking at your picture (thanks) and after thinking about it further, would placing multiple magnets in a straight line not cause the damping to vary as the spindle "sees" additional magnets as it moves toward the rear? What I plan on trying is one single magnet on either side of the manifold, as close as possible to the manifold.
Regards. |
I think the home depot link blew the last post up like that.:^( Just want to clarify when I said. Richard – did you have the lead slug in your spindle when you were using the magnets and was it at 12 PSI? I want to recognize that you are running a custom setup spindle/manifold. My experiences have been with stock spindles 2.5 and 2.0. Still - I assume you tried magnetic damping with the lead slug and without ? Cheers |
Dover
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 Well I have to say am very impressed with your flexibility Dover. I am very happy that I run every day for my health. But I can’t even touch my toes. I guess I should start Yoga..with my wife. Frogman – your observations are similar to mine and the reason I am still using the magnetic damping. Here is how I am currently set up. ET 2.5 Magnetic damping What is not obvious in the pic is that there is actually over one inch of clearance between surface and spindle when it comes across. Can the positioning be improved ? Will try three on top of one another. I just placed three for even distribution as the spindle comes across. I am assuming placing any magnets directly under the manifold will have a reduced effect ? I could try this with the ET 2.0. Home depot has a large selection of various magnets. http://www.homedepot.com/webapp/catalog/servlet/Search?storeId=10051&langId=-1&catalogId=10053&keyword=magnets&Ns=None&Ntpr=1&Ntpc=1&selectedCatgry=Search+AllMy wire exists at the armtube. After getting the Dynavector gauss level info about using thousands of gauss in their tonearm – these 50 (approximate) gauss magnets seem harmless enough ? Many variables here including air psi. Different PSI’s do affect how the spindle reacts based on my direct experience and discussed here already. Eddy Current with a floating modelMy experience with the stock ET2 and 2.5 spindles – I am no scientist – is the higher the PSI the less force required with magnets and the smoother (the motion will be). I use 19 PSI. The ease with which the spindle goes through the manifold at higher PSI is obvious. Try 3 psi and 20 psi to prove this. I have also said this before here - When my cartridge is raised and at rest – at 19 psi - I can blow on it and it will shoot across the top of the LP. Also whether it is a 2.5 or 2.0 spindle. I would assume that the 2.0 spindle being smaller reacts more to less magnets? But the differences could be subtle? Richard – did you have the lead slug in your spindle when you were using the magnets and was it at 12 PSI? Cheers |
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. |
Thanks Dover, Ketchup and Richard for addressing my concerns.
Well, I must admit I was somewhat skeptical about magnetic damping, but I am now convinced of the benefits. Some preliminary observations:
So far, I have used a single refrigerator magnet that conveniently detached itself from the back of a cooking timer. I glued this inch-squared flat magnet to a small block of glued layers of cork about the same size as the magnet. I situated it on the wand side of then arm pillar; frankly, only because I still have the damping trough attached to the pillar (with paddle disengaged). I plan on trying it on the other side, as well as trying other, more powerful magnets. The magnet is as close as possible to the spindle without touching it.
I listened to the same musical selections several times, with and without the magnet. The results are relatively subtle but unmistakable. There is a general "cleansing" of the sonic picture; as if a fine mist is removed. Bass definition is improved with an increase in one's ability to hear pitches in the bass; as opposed to simply low frequency energy. The highs gain a bit of refinement and sound slightly less ragged. On "The New Breed" from Donald Fagen's new release Sunken Condos, Walt Weiskopf plays both alto and tenor saxophones. Without the magnet, it is very difficult to hear when he plays alto vs tenor. With the magnet, more of each horn's individual character can be heard. Also, for an LP with otherwise very good sound, the bass, while being powerful and very well extended, has a strange "drummy" quality with less than good definition. The magnetic dampening brings a welcomed slight improvement in pitch definition. Curiously, the soundstage seems slightly smaller with the magnet; perhaps a result of the increase in control and definition. The differences are not earth-shaking by any means, but definitely worthwhile. I have not experienced increased volume; perhaps with the more powerful magnets.
Biggest surprise of all: record surface noise seems reduced. LP surfaces are quieter, and the loudest clicks and pops sound less obtrusive with a more subdued character.
More to follow. |
There is a sound engineering reason to put any mag dampening to be at the wand end of the spindle. Since the mag tends to resist spindle movement, it acts as a pivot for any non axial spindle motion
Since the cartridge is at the end of the wand and not at the end of the spindle, there is a force moment induced by stylus movement. The spindle can, at frequencies below the air bearing resonance point, move about this pivot point in a non axial manner.
Having this pivot point at the wand end causes less teter totter due to spindle sleeve clearance than would be the case if the pivot point was at the counterweight end. This benefit is clearly audible.
Exactly the same design feature is present in TT's with inverted main bearings.
Of course the mag is closer to the signal wires.
The choice is yours. |
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. |
Hi John47 :^) - raising fraternal twins can be entertaining too. My wife and I are into our 18th year of dealing with their demands in “stereo”. This hobby and a little sense of humor has helped me through it to this point. The twins have shaped my humor however – made it more cynical I think. My wife doesn’t care too much for it. She also doesn’t care for music above 70 db. Probably explains why I am here.
Rugyboogie - welcome to the thread. Am curious if you or other Kuzma Airline owners have ever considered any modifications to that tonearm?
Cheers |
Richardkrebs
Chris
I initially used one fridge magnet then went to multiple fridge mags. Finally using Neodymium before abandoning the idea.
I tried first at the counterweight end then transferred to the wand end. There are differences. Now the reasons for that could be a whole new controversial discussion.
Richard - We are all big boys here and we all know this hobby has a lot of controversy as it is based on preferences. Please do share the differences you found. |
Great thread and thank you to all that have contributed to this thread.
As a tangent tracking fan this ET thread is providing me with some very interesting viewpoint and insight on the working of this tonearm. |
Chris
I initially used one fridge magnet then went to multiple fridge mags. Finally using Neodymium before abandoning the idea.
I tried first at the counterweight end then transferred to the wand end. There are differences. Now the reasons for that could be a whole new controversial discussion.
Frogman
As per an earlier post, when I rebuilt the manifold I used 2 shims and one grub screw arranged at 120 degree increments each end of the manifold. This allowed for tightening by doing up the grub screws. Do this on a standard manifold at your own risk
Ketchup
You got me running to the arm to check these little screws. Still tight after 15 years, phew.
So now some may be asking why I haven't cleaned the sleeve in 15 years.
Well, we do have very clean air here in NZ.
With the air pump running I break the air line next to my pressure gauge and squirt in CRC CO contact cleaner. Then reconnect.
I have previously placed paper towels at each end of the manifold. Then move the spindle back and fwd.
The cleaner is forced thru the sleeve and its tiny orifices. Leaving them to be nice and clean
I do this approximately every 6 months with positive results. |
Very entertaining Chris, much mirth.
"I took one of the small circle magnets from the ET2.5 setup over to my Dynavector tonearm. What followed kind of reminded me of one of those horror movies –you know the one where the guy wakes up and finds himself magnetized in a kitchen; pots and pans, knives start flying towards him getting stuck on him as he ducks.
ok - no pots and pans or knives here. But I did LOSE the magnet as it flew out of my hand. I had to search to find where it had lodged itself." |
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. |
Ketchup, I am intrigued by your idea of shims replacing the O rings in order to increase the rigidity of the bearing. I am confused however. Don't the O rings need to remain in place in order to keep air from leaking out of the manifold? What type of shim are you referring to, that is both very rigid and will seal the outer diameter of the manifold to the housing? Are you suggesting to place shims inside the manifold housing, between the OD of the manifold and the ID of the housing? Frogman, The shims will not replace the o-rings- they will be added to a completely stock, unmodified arm. The way the arm is built, there is about 3/16" of "free space" between the manifold and manifold housing before the o-rings. To illustrate what I mean: Cut a piece of paper into a thin strip 1/8" wide and an inch long. Slide the piece of paper into the gap between the manifold housing and the manifold. It should slide in about 3/16" before it hits the o-ring. That space is where the shims will go. Here's a photo of my ET-2.5 manifold that shows the 3/16" gap: ET-2.5 manifoldI like Richard's idea of making them tapered, but my OCD will have me constantly worrying that they have moved. A good compromise would be to make two of them non-tapered and make the third one tapered to apply the necessary force to lock the manifold in place. A small dab of silicone should hold the tapered shim in place and will be completely reversible. |
Gentlemen, fantastic and very interesting reading over the last few days; thank you.
Dover, I want to try magnetic dampening. Could you please provide some more details about the positioning of the magnet for your magnetic dampening tweak? Did you place it between the manifold housing and the front edge of the tt, or between the manifold and the rear of the tt? Also, how did you orient the magnet's polarity? Does it matter?
Ketchup, I am intrigued by your idea of shims replacing the O rings in order to increase the rigidity of the bearing. I am confused however. Don't the O rings need to remain in place in order to keep air from leaking out of the manifold? What type of shim are you referring to, that is both very rigid and will seal the outer diameter of the manifold to the housing? Are you suggesting to place shims inside the manifold housing, between the OD of the manifold and the ID of the housing?
Chris, thanks again for starting what is currently, and without a doubt, the most interesting thread on the subject of LP playback on the 'Gon; IMHO.
Slaw, if you're still out there: what happened?
Regards to all |
A real interesting read for me the last couple of days. Ketchup please keep us updated on those shims and I hope you get "one" of your arms up and running soon. Yes I was referring to the compliance between the “spindle and manifold” only. Sarcher30, John47 welcome to the thread. Excellent video link Ketchup. The ET2 tonearm no magnetic parts to be found anywhere on the tonearm itself. Put a magnet to it and find out for yourself. The cartridge itself, well don’t put a magnet there.....how close is ok or is it ? It got me curious. I hate unknowns. I have been reading both Richard and Dover’s positions on it. Have learned alot. I have something to share regarding these magnets, magnetism and it has to do with my Dynavector tonearm. I took one of the small circle magnets from the ET2.5 setup over to my Dynavector tonearm. What followed kind of reminded me of one of those horror movies –you know the one where the guy wakes up and finds himself magnetized in a kitchen; pots and pans, knives start flying towards him getting stuck on him as he ducks. ok - no pots and pans or knives here. But I did LOSE the magnet as it flew out of my hand. I had to search to find where it had lodged itself. Under one of the magnetic dampers near the DV505 base is where I found it. There is a little bolt (magnetic) on the left side of the main arm (as it has two arms). This is not shown on the tonearm diagram. Its helps with antiskating. As you get a few inches away from the post where the arm rests, the current draw is noticeable. The cartridge itself is about 6 inches away from this position which seems to be the last spot where a magnet field exists. On my ET2 arm the actual cartridge position because of it design is much further away. This got me curious so I sent an email to Masaaki at Dynavector asking about these magnetic levels. I’d like to say that Masaaki has to be one of the friendliest and knowledgeable audio people I have come across over the years in this hobby. Always responsive to my questions. I asked him for information about the “magnet force” levels on the Dynavector tonearm. His response. Hello Chris,
Unfortunately we cannot publish data of measured magnet current levels used the flux damper magnet in the DV505 tonearm. Only information is that the Magnetic flux density was multi-thousand gauss.
Thank you and best regards,
Masaaki
Dynavector
Multi – thousand gauss ? what does that mean ? Gauss Unit/Levels • 10−9–10−8 gauss – the magnetic field of the human brain • 0.31–0.58 gauss – the Earth's magnetic field at its surface • 25 gauss – the Earth's magnetic field in its core[3] • 50 gauss – a typical refrigerator magnet • 100 gauss – a small iron magnet • 2000 gauss – a small neodymium-iron-boron (NIB) magnet • 600-70,000 gauss – a medical magnetic resonance imaging machine • 1012–1013 gauss – the surface of a neutron star[4] • 4×1013 gauss – the quantum electrodynamic threshold • 1015 gauss – the magnetic field of some newly created magnetars[5] • 1017 gauss – the upper limit to neutron star magnetism; no known object in the universe can generate a stronger magnetic field[5] I am trying to figure out why Dynavector would use Gauss levels in the multi thousand range? Would they not have measured its affect on the phono signal ? From the DV505 manual - similar info to the previous posts. electro magnetic damper
This damper applies effect of eddy current, which is generated when conductor moves in magnetic field, and which obstructs conductor in motion. It has almost no damping effect on motion of non-vibrating tone arm, but is highly effective to vibration of arm, such as arm resonance. DV505 Manual Richard – can you tell us what type of magnetic damping you experimented with that led to your opinion of it? Position of the magnets relative to the arm, Gauss levels ? Dover - I believe you were using a fridge magnet ? which is about a gauss level of 50? Cheers |
|
First an observation as I read what Ketchup and yourself said about the compliance in the air bearing spindle.
Ketchup do you notice any difference in force required to move the spindle in your ET 2.0 and ET 2.5 with no air on?
My ET 2.0 spindle can be forced through the manifold with no air. There is quite a bit of resistance but it can be done. This is normal according to Bruce. And its anodized coating prevents any damage.
My ET 2.5 spindle will not move – it is really tight. There is not much movement at all without air. It has to be really forced. Chris, The compliance that Richard and I were talking about was in the o-rings between the manifold and the manifold housing. No matter how much air pressure you can get between the manifold and the spindle (making it very rigid), you will always have the squishy o-rings causing the spindle and manifold to move within the manifold housing. Not rigid = not good, hence the shims. Most other linear tracking, air bearing tonearms don't have o-rings to soften up the bearing. I believe that getting rid of this compliance may have a huge effect on performance as Richard suggested. I WILL be doing this after I get my system set up and I'm familiar with the sound without the shims. When I bought my ET-2.5 arm I actually did notice that it was a little difficult to move in the spindle with no air. I assumed that the spindle was out of round, but it worked fine with 1 psi in it when I did the air flow tests. Looking back at my notes from the air flow tests, I observed dragging at 1 psi with the ET-2 (set up on a TT with the arm wand, cartridge, and counterweight) but did not experience dragging with the ET-2.5 at 1 psi. The ET-2.5 setup did not have an arm wand or counterweight attached, though, so it's apples to oranges. The dragging with the ET-2 was most likely due to the added weight of the arm wand, cart., and counterweight. Also, I showed Bruce the results of my air flow tests and he said that both my ET-2 and ET-2.5 tonearms were set up for high pressure. I should have mentioned this earlier... |
|
Of course much more important is what effect do these eddy currents have - must have negative effects. Has it ever been objectified ? |
"you misunderstand how it works".
Not so.
Please reread my post.
I was referring specifically to the static effect - hold a magnet near apppropriate metal: does it have zero effect? |
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. |
“Magnetic dampening will vary with the speed of horizontal motion whereas the added mass approach is simply increasing static inertia considerably.”
"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."
How was no static magnetic effect achieved: did you switch off the magnet? |
Dover.
I pretty much agree with everything you say. Where we diverge is in the sublties. It is easy to add too much mass in the horizontal plane. I went there in my tests. The trick is finding a compromise point.
Dynavector put the reason for high horizontal mass far better than I could. I agree with their conclusions.
Sarcher30 Dynavector's quote covers their views on this.
Further, from memory, the ET in standard form has a horizontal to vertical effective mass ratio of around 6:1. So it is already a differential mass arm. It is just that in my view this ratio is not enough. As per before I don't care what people think about this, they are free to give it a go, or not.
Also as before, I like what Mag dampening does right, I just cannot put up with what it does wrong. |
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. |
Richard, To take advantage of the Dynavector tonearm design wouldn't it require a cartridge with different compliance in the two planes? Otherwise wont only one plane will be optimized with the Dynavector arm? |
Chris. Thanks for the comparison notes. I now have a clear picture of the differences.
The Dynavector arms have always been fascinating to me due to their radical design. Magnetic dampening and for a pivoted arm the unusual idea of deliberately different effective mass in the vert and horiz planes. Both of these features being recently discussed in this thread.
Have only listened to 2 of these beautiful arms and in systems that I am unfamiliar, so cannot draw any concrete condclusions.
I have included a quote here from their manual on the 507 should anyone be interested.
• 3 Bi-axis inertia separation for accurate signal reproduction and superb tracking ability
"Bi-axis inertia separation" may sound complex but it simply refers to a tone arm having two arms which operate independently in the horizontal and vertical planes. In contrast, a conventional tonearm has only one arm which moves both horizontally and vertically. This is called a gimbal type tonearm and the inertia for both planes is the same.
The DV507 bi-axis tone arm has a large inertia for horizontal movement and a very small inertia for vertical movement. We shall now explain the reasons why this is advantageous.
It is well known that a cartridge generates an audio signal by the differential motion between the cantilever and the cartridge body. Consequently, if the supporting point of the cartridge (the tonearm) vibrates, the tonearm motion affects the audio signal.
In these conditions, the signal, which causes the tonearm to vibrate is of low frequency and large amplitude.
In the currently used 45-45 stereo record cutting procedure, low frequency signals are almost entirely recorded in a horizontal direction. This means that the low frequency signal, which can cause vibration in the tone arm, exists only as a horizontal force.
The tonearm therefore must have sufficient effective mass and rigidity in the horizontal plane in order to provide a stable platform for the cartridge.
On the other hand, for the mid to high frequencies, the effective mass of the tonearm should not be too large since the combined mass of the cartridge and the head shell need to be taken into account as well. In particular, where records have a warped surface, the vertical effective mass needs to be small enough to ensure a good tracking ability on such surfaces.
To summarise, the tone arm should have a large effective mass and enough damping in the horizontal plane and at the same time a small effective mass in the vertical plane.
These conditions are almost impossible to achieve with a tone arm of conventional design using a simple gimbal pivoting system. To solve the problem, Dynavector designed a bi-axis, inertia controlled tonearm where the shorter and lightweight vertical sub arm is placed at the end of the horizontal main arm. This is the special feature of our design. |
Richard, My ET 2.0 versus the ET 2.5 – both have high pressure manifolds. First an observation as I read what Ketchup and yourself said about the compliance in the air bearing spindle. Ketchup do you notice any difference in force required to move the spindle in your ET 2.0 and ET 2.5 with no air on? My ET 2.0 spindle can be forced through the manifold with no air. There is quite a bit of resistance but it can be done. This is normal according to Bruce. And its anodized coating prevents any damage. My ET 2.5 spindle will not move – it is really tight. There is not much movement at all without air. It has to be really forced. Bruce built it a few years ago for me. It was designed to run at 19 psi. Unlike my ET 2.0 which will run at 19psi and a low 3 psi as well, my ET 2.5 will start binding up if I drop the pressure – not sure what the actual PSI number is. The spindle starts resonating above a certain psi. We have discussed this here before. The consensus seems to be this PSI number varies just like our individual setups. For me its 19 psi and the reason I had the arm made for that psi. Richard as far as sonic differences with me. Let me use an analogy. We have all seen those graphs that show motor oil and the difference between lets say 5w30 and 10w30 motor oil at different temperatures. http://i36.photobucket.com/albums/e29/2002neonrt/35graph.jpgLets assume lower temperature represents lower compliance / heavier cartridges – that is the ET 2.5 5w30 and the ET 2.0 is 10w30. Both overlap and work well within a large range for both MM and MC. But when the setup is tweaked/improved I think the ET 2.0 works a tad better with MM and ET 2.5 with MC. Does that analogy make any sense? People assume the ET 2.5 is better because it is (.5) the next newer version. It depends. It came after so the obviously the parts themselves are newer but as far as sonics go ? well we know the smaller diameter 2.0 spindle according to Bruce resonates at 5-6 hz. The 2.5 resonates at 2-3 hz. The armtubes are the same as far as I know for both versions. Aluminum original one better with higher compliance, CF – middle ground – Magnesium – for really low compliance. This is the advice from Bruce with the testing he has done. The ET 2.5 sucks more air – has more volume. When they were in the same room I remember how the pressure gauge when I unplugged one for other would move by a few PSI. Ketchup’s graph shows this too. The ET 2.0 was around when vinyl was in its heyday along with MM cartridges. Then came MC cartridges and BT adjusted (I guess) to the time and introduced the 2.5 with its lower resonance. Just an opinion. If all things were the same – apples to apples - We know that will never happen. The ET 2.0 seems to handle a little better with lighter higher compliance MM’s. Like a lighter sportscar with great handling. But add a bigger motor to the sportscar (heavier MC/stiffer/lower compliance ) and I feel the ET 2.5 handles a little better. Bigger diameter spindle along with the lower resonance. A very rigid spindle to manifold coupling in my 2.5. The differences are not day and night. The MM 420str sounds great on the 2.5. Its just seems to be a little more ease on the 2.0. Bruce’s review of the 420str kind of confirmed this to me too. So I use MC on my 2.5 and MM on the 2.0. The rooms are adjacent to one another in the basement. Hope that helps. Richard you mentioned that you studied the Dynavector arm. Did you take any measurements of it - Impressions ? Cheers |
Chris
My apologies if this has already been covered in the thread, but can you tell us the sonic differences between the ET2 and ET2.5
Many thanks |
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. |
