'Audio' review of the ET-2. Excellent read with some (if you haven't already read it) surprising, even startling, results. By Edward M Long in 1987, when reviews were a serious affair. As I'm semi literate, Chris has kindly uploaded my jpegs to his site. Thankyou Chris. Go to http://s1173.photobucket.com/user/CT-993/library/?sort=2&page=1 (it works, I've tried it) and you will find 7 pages of review, including v interesting measurements. I did try to post this review here, but that cann't be done presently. Sorry guys if this duplicates an earlier ET-2 post. I haven't read every one of well over 700 posts. |
Dover
I do wish you would stop repeating your fundamental error ad nauseum.
BT measured a rise in response of 6-12 db at the resonant frequency. Say 3 to 8 hz. I don't call these frequencies bass.
Bruce measurements show that this rise in response is reduced by 8db with the addition of an oil trough. This in test conditions which used a deliberately high Q and a low compliance cart. The amplitude of resonance decreases the further you move away from Fr. BT suggests that resonance effects frequencies up to 3xFr.
My rigs Fr is just above 5hz, almost 4 times lower than what is normally accepted to be the lower bass, 20hz.
There is no rise in bass response in my system. |
05-17-13: Ct0517
As I type this Ottawa to Toronto area of Ontario experienced a 4.8 earthquake – a little shakey.
Sort of like my JMW 12 unipivot. :^) My local audio shop has been selling VPi’s for some years. In my experience if the arm is wobbling then it is either not set up correctly or perhaps the bearing needs checking. As a matter of interest, the Aro is inherently more stable than the VPI and most unipivots as the bearing is a radius tip sitting in a cup with a defined radius. This provides damping of around 2db, is a true mechanical ground and is self centering. With the VPi the tip is upside down – the cup sits on top of the tip, so it is less stable, and is not a true mechanical ground. Stereophile review ARO – June 1993
Unipivots have traditionally been only marginally stable, but much thought has evidently gone into the ARO's design. Lowering the counterweight to about record level has given the ARO excellent stability. This also lowers the center of gravity to below the pivot point, providing about 6dB of mechanical damping of the stylus. Another 2dB or 3dB seem to come from the bearing cup, which has a sapphire insert. The bearing is the ARO's stroke of genius. In other unipivots, a sharp pin is mounted to the turntable and the arm carries a cup which sits atop the pivot point. The ARO's arm carries the sharp tip, resting this atop a stationary cup: a true mechanical ground I can run an extremely eccentric record or a warped record and the ARO remains incredibly stable – there is no wobble or change of azimuth when disturbed. |
05-15-13: Richardkrebs
In Bruce's paper on the oil trough he talks about the effect of Fr being apparent at 3x its frequency. Targeting say the 12 hz you mentioned would mean that it is causing phase and amplitude problems at 36 hz. This is not good. 05-16-13: Richardkrebs
Dover.
Secondary resonance? You mentioned this twice in your post 05-15-13. The frequency numbers you used were 3x Fr for this. The 3x Fr figure is the multiplier used by BT where he considers the amplitiude and phase anomolies above Fr have fallen to a level that is benign. Richardkrebs, according to your own posts 05-15-13: Richardkrebs - There is a phase and amplitude problem at 3xFr 05-16-13: Richardkrebs - There isn't a problem at 3xFR Of course I agree with your first statement. The second is wrong. 05-15-13: Richardkrebs
Note also, Bruce set up the arm with a "deliberately high Q" and low compliance cartridge. Richardkrebs your statement is misleading. Bruce added 18g of horizontal effective mass with the damping trough mechanism. You have added 62g of mass to your arm by adding lead and removing the decoupled counterweight. Assuming your example of 9g cartridge and 32g of counterweight plus your added lead of 30g then; The horizontal effective mass of the ET2 with damping trough is Std ET2 - 25+9+18=52g KREBS ET2 - 25+9+32+18+30=114g If you believe that you can increase the horizontal mass of the ET2 from 52g to 114g and get the same results as Bruce Thigpen, then that is where you are wrong. 05-15-13: Richardkrebs
See BT's own formula for calculating horizontal Fr. It does not take into account these other structural resonances.
That said these other resonances can have an effect on the shape of the resonance curve but the fundamental determinent is the horizontal mass. Ok, so you disagree with me, then in the second sentence you agree with me. I'll take the second view. If the fundamental determinant is horizontal effective mass, why do you expect the same results as Bruce Thigpen when you have more than doubled the horizontal mass with your changes to your ET2. The other key issue with running high horizontal mass, far higher than recommended by Bruce Thigpen, is the increased tracking distortion that this causes. I quote from Bruce Thigpen:
If the weight is coupled the system resonant frequency would be extremely low, a resonant frequency at 3Hz with a significant rise in response (6-12dB) results, which would affect tracking slightly because of the asymmetric position of the cantilever, we opt for splitting the horizontal resonance frequency into two points and lowering the "Q" which improves tracking.
More important than tracking, the intent was to reduce the modulation effects of low frequency energy (FM and AM) that increase distortion in the cartridge,
To reiterate, from my listening experience increasing the horizontal mass and removing the decoupling of the counterweight on the ET2 slugs the sound and the distortion can be clearly heard. |
Richardkrebs has advocated adding 60+g of horizontal mass by adding lead to the bearing spindle and removing the decoupling mechanism of the counterweight. With the ET2 the decoupling of the counterweight is part of the strategy to keep horizontal mass not too high. I'm not sure if there is any (groove tracking) disadvantage in having Eff Mass too high, ie. Res Freq too low. Sure, there may be issue with particular TT suspension or TT support resonances, but arguably not detrimental to good record tracking? |
Richardkrebs has advocated adding 60+g of horizontal mass by adding lead to the bearing spindle and removing the decoupling mechanism of the counterweight. With the ET2 the decoupling of the counterweight is part of the strategy to keep horizontal mass not too high. I'm not sure if there is any (groove tracking) disadvantage in having Eff Mass too high, ie. Res Freq too low. Sure, there may be issue with particular TT suspension or TT support resonances, but arguably not detrimental to good record tracking? |
With regard to the high horizontal mass the standard ET2 has a very high horizontal effective mass as standard ( 25g plus the weight of the cartridge ) compared to a pivoted arm. However the FR64 of course, has Eff Mass of 30-35gms (or more). |
Further...
Mono signals of course, do result in horiz groove modulations. |
As I type this Ottawa to Toronto area of Ontario experienced a 4.8 earthquake – a little shakey. Sort of like my JMW 12 unipivot. :^) |
What an extraordinary hobby this is. RK and I share this wonderful aluminum ET2 Gooseneck that he made - I really like it.
At this current (snapshot) in time however;
RK’s tonearm objective is adding more control and damping to his Krebs Arm.
I meanwhile am trying to figure out how to go wireless with my ET 2.5.
Think Free Willy !
Maybe my IT background biases are showing. With that the damping fluid should be coming early next week with the adhesive tape. Look forward to trying it again after all these years.
Welcome to the thread Spock15. Listing what your air bearing and pivot arms are would be nice to those of us reading for reference.
Thekong has provided some excellent perspective between the Rockport and ET2.
Hi TheKong – were you able to find the lead to make the counterweights at those tire shops ?
Look forward to Rugyboogie providing perspective with the Kuzma Airline and ET2 soon – Congrats on getting an ET2 - RB.
Now we need a Swedish fellow or gal :^) to come on here to help provide perspective on the Air Tangent and ET2. Maybe I will look for one (Air Tangent) to close this loop. However no remote control version for me.
As I type this Ottawa to Toronto area of Ontario experienced a 4.8 earthquake – a little shakey. |
One is usually coloured/informed by past experience. Coincidentally, I have a couple of FR64S's myself & you reminded me of the Hadcock GH228 that I have gathering dust.
Another recent unipivot, an Apparition 12" superseded the above. A very fine performer, to the extent that I have had little compunction to A/B with the older arms. A very top shelf pivoted tonearm in my humble experience.
Nothing is perfect in this game (audio & life in general ;)) but with my linear tracker (a Trans Fi terminator) I find the combined qualities of genuine low distortion, wide bandwidth, dynamic stability...are overall most persuasive. Are these attributes typical of linear trackers? I can't be sure at this point.
Regarding Effective Mass...with record groove modulations cut at 45deg, as we know, I think it's not entirely useful I think to dwell on Effective Mass in terms of horiz & vert properties.
Cheers. |
Spock15
I currently own an ET2, Naim Aro & Hadcock unipivot and have just sold off my Bluenote Borromeo ( Titanium tubed unipivot ).
I hear a crisper articulation of the leading edge with all three unipivots. It's not large. The Aro is better in this regard than the Bluenote & Hadcock. I do agree with you that effective mass, both horizontal and vertical contribute to the "squarewave".
With regard to the high horizontal mass the standard ET2 has a very high horizontal effective mass as standard ( 25g plus the weight of the cartridge ) compared to a pivoted arm.
Richardkrebs has advocated adding 60+g of horizontal mass by adding lead to the bearing spindle and removing the decoupling mechanism of the counterweight. With the ET2 the decoupling of the counterweight is part of the strategy to keep horizontal mass not too high.
Bruce Thigpen has measured, not theorised, actually measured on the ET2 a 6-12db lift in bass response when increasing the horizontal effective mass by 30g ( removing the decoupling ). From what I have actually heard, in a real system, since I have owned an ET2 from the mid 80's, increasing the mass slugs the sound and robs the music of musical pace and timing. Most of the contributors on this thread ( Frogman, Slaw, Ct0517 & myself )have found big improvements when carefully tuning the decoupled counterweight, as predicted by Bruce's testing.
By the way I still own a Dynavector 501 which has a very high horizontal effective mass, and whilst the bass is quite punchy, the musical timing, soundstaging, and resolution is well down on both my Naim Aro and Fidelity Research FR64S ( yes I own 2 of these as well ).
|
Dover.
Secondary resonance? You mentioned this twice in your post 05-15-13. The frequency numbers you used were 3x Fr for this. The 3x Fr figure is the multiplier used by BT where he considers the amplitiude and phase anomolies above Fr have fallen to a level that is benign. Think a normal distribution curve. In our industry, we use a 6x Fr multiplier since we operate in a much more conservative environment.
There is no 6-12db increase in amplitude at 3x Fr or even Fr. The arm is damped with an oil trough. See the graph and read the technical notes from BT, posted by Chris on 05-14-13. Note also, Bruce set up the arm with a "deliberately high Q" and low compliance cartridge.
You let slide and error in my calcs because other parts of the arm have their own resonance. Sorry No. See BT's own formula for calculating horizontal Fr. It does not take into account these other structural resonances.
That said these other resonances can have an effect on the shape of the resonance curve but the fundamental determinent is the horizontal mass.
There are 2 possibly 3 structures in a standard ET who's own resonance is low enough to have this impact. The decoupled counterweight, which is deliberate. The relatively compliant gooseneck and the o'rings in the manifold. The o'rings are a maybe since they typically allow movement towards and away from the record, not laterallly.
(Anyone interested in observing how compliant the goose neck is could try this test. Do it at your own risk!
Lift the arm with the lifter and put the stylus guard on. Travel the arm fully inwards and then lightly push the spindle where the wiring plug is against the bearing sleeve. Now lightly pull the cartridge end of the wand towards the outer edge of the record. You can clearly see deflection of the wand. The goose neck is flexing. If you are able to let it go quickly, you will see it momentarially oscillate. If chris did this with the aluminium goose neck he would need to literally bend the wand to get any deflection.)
All three of these structures have been altered (stiffened) or eliminated in my arm since in my opinion they all compromise "leading edge" and have other negative consequences.
The other compponents of the standard arm have, IMO less impact on leading edge performance with the airbearing having none at all. It's resonance is in the 100s of Khz, way outside the audio spectrum. Spock15's experience with his air bearing arm seems to support my view. However it is the cacophony of all of the individual resonances amongst many other factors that makes up the "sound" of the arm. On that front we agree.
|
Pseudo science from Dover:
"removed their fluid damping and replaced it with electromagnetic damping which has the benefit of not inhibiting movement until the movement happens."
Pseudo science: its identical with fluid damping - there is no damping unless there is movement (same with the dampers, so called shock absorbers, on your car. Drive slowly over a speed hump and the whole vehicle is raised, ie there is no movement, and no damping). |
05-15-13: John47
Bruce Thigpen:
"The ET-2 with the
damping trough will exhibit almost perfect low frequency phase response."
You don't like the ET-2 set up to have near perfect low frequency phase response?
Thats fine, its a free world, but it means you accept/enjoy DISTORTION. No I dont believe Bruce Thigpen does enjoy distortion. On the contrary Bruce Thigpen has cleverly designed an arm that tracks superbly and can be fine tuned via the adjustable VTA, Azimuth, and decoupled counterweight. Bruce Thigpen does not add 60g+ of horizontal effective mass and remove the decoupling of the I Beam. The perfect phase response that Bruce obtains with the damping is achieved by operating the arm within its design parameters. Keeping the horizontal mass as low as possible is part of the design. Adding 30g of lead to the arm and removing the counterweight decoupling will indeed create significant distortion, including an inflated bottom end and phase anomalies, but that is not how Bruce runs the arm. |
Chaps...I'm not an ET user nor an Aro user, but I do use both a 12" unipivot + an air bearing linear tracker, so if I could be permitted to offer a humble opinion, hopefully useful to the topic ;)....
In this game, sometimes we tend to think about what we SHOULD hear, rather than what we DO hear...
In principle, the tolerance gap of a air bearing leads us to think that an air bearing will be therefore compromised sonically - ie. because it will never have solid bearing contact. However I hear no lack of 'leading edges' with a linear tracker. So what is going on?
On the topic of 'leading edges', I think a 'square wave' is an appropriate analogy. The leading edge of square wave (rise time/slope, overshoot control...) is determined primarily by the HF component of the signal/tone. In the same way, the perceived 'leading edges' of sound is poor, if the HF harmonic component of music signal is compromised.
A unipivot typically has excellent HFs, owing to absence of 'bearing rattle'. I also hear excellent HF tone & extension with an air bearing tonearm. Go figure...
The explanation I think is that, at groove modulation frequencies, it is not the rigidity of the bearing that is key, but rather the inertia of the tonearm, as 'seen' by the stylus, that is key. From this perspective, a pivoted tonearm rotates freely, ie. has very low (rotational) friction.... and a linear tracker also has low (linear) friction. Both are similar... but from the viewpoint of the stylus in groove, 'inertia' or Effective Mass (at groove modulation frequencies) must be high - adequately high to reproduce LF signals without resonance/loss of power delivery.
Contributes to the discussion I hope.
(Apologies if this is old ground, I haven't managed to read all 700 pgs ;) ) |
05-15-13: Richardkrebs
Dover.
My calculation of weight delta was based on how much weight the air bearing has to carry. Not the horizontal effective mass. You voiced concern that I had taken it outside its load carrying capability. Optimum load capacity. You have added 30g of lead to the mass the bearing has to carry. This has 2 negative effects - it pushes to mass to the extreme and one would redesign the bearing if one were knowingly going to operate the arm at a higher mass level. Secondly the added mass will impact the shearing forces involved - the arm is not frictionless and the bearing is not absolutely rigid - these are some of the reasons why users are hearing different results with higher pressures. As a point on your calculations on FR I led slide the error in your calculations - the bearing has a resonance, the bearing tube has a resonance and the total resonance will be a sum of the resonances inherent in the arm. One really needs to measure the resonances to see whats going on , thats why Bruce does extensive testing. The maths you are using for FR calculations is not the complete story. 05-15-13: Richardkrebs
Re heavy arms. I assume you are saying that ANY heavy arm, and this includes the Rockports, Walker and Kuzma have serious problems with distortion. Further, by implication, you are saying that the owners of these arms are deaf to these distortions. I think you should use the word preferences, when making judgments on other folk, but certainly they may well be. Some folk like fat bottom ends others prefer speed and musical timing. For me music is about timing and nuance - I can certainly hear the slugging of the sound and loss of musical timing when adding too much horizontal effective mass to the ET2 as others in this thread have also found when they removed the decoupling from the I Beam. You may also like to read the comparison of the Kuzma to the Walker in the Absolute Sound mag December 2006 where the reviewer articulates the differences - the Kuzma being dark and solid vs the Walker having more of "the "gestalt" of a live concert, more lifelike presence of instruments, their colors, their dynamics, and the space they play in" of the Walker "fuller, more realistic in tonal color, bigger, bloomier, wider, deeper, more layered in soundstaging, and a bit more authoritative dynamically". 05-15-13: Richardkrebs
Targeting say the 12 hz you mentioned would mean that it is causing phase and amplitude problems at 36 hz. This is not good. Depends how big the amplitude problems are. Some of the heavy arms you have mentioned have additional measured resonances at 100hz & 200hz. In your case you you have reduced the theoretical resonance from 8.08hz to 5.17hz. so yes you have a small residual at 24hz in a standard unmodified arm - but this is outweighed by the amplitude of the resonance being much higher when you added 62g of horizontal effective mass. Furthermore that small secondary resonant peak at 24hz with the standard arm can be dialled down with careful tuning of the counterweight spring. I very much doubt whether many systems are truly flat to 20hz in a real home environment. In your case you have shifted the secondary resonance from 24hz to 15hz, but have increased the amplitude of the 15hz resonance substantially - probably 6-12db higher in amplitude compared to the smaller resonance at 24hz with the arm as standard. |
Bruce Thigpen:
"The ET-2 with the
damping trough will exhibit almost perfect low frequency phase response."
You don't like the ET-2 set up to have near perfect low frequency phase response?
Thats fine, its a free world, but it means you accept/enjoy DISTORTION.
BTW, as you haven't run an ET2 for heading towards two decades, isn't your credibility suspect? |
Dover.
My calculation of weight delta was based on how much weight the air bearing has to carry. Not the horizontal effective mass. You voiced concern that I had taken it outside its load carrying capability. My calculation is correct since the bearing is supporting the weight of the counterweight, it is designed to take the heavier magnesium wand, the full counterweight complement and heavier cartridges.
Re heavy arms. I assume you are saying that ANY heavy arm, and this includes the Rockports, Walker and Kuzma have serious problems with distortion. Further, by implication, you are saying that the owners of these arms are deaf to these distortions.
We will have to agree to disagree on where we should target the horizontal Fr. In Bruce's paper on the oil trough he talks about the effect of Fr being apparent at 3x its frequency. Targeting say the 12 hz you mentioned would mean that it is causing phase and amplitude problems at 36 hz. This is not good. |
Oh, it just dawn on me, could the "less smooth" of the Rockport bearing cause by the flex of tiny airhost? If it is, then the airhost actually provide considerable "damping"! |
05-14-13: Richardkrebs
.. if my heavy ET has problems with cantilever flex, bass boost, phase shift and so on; so do the other heavy arms. Rockport, Walker, Kuzma. This because the horizontal effective mass is solely determined by the total weight that is moved sideways at the frequency of interest, since all of these designs are virtually frictionless. Thats correct and thats why the lower mass ET2 has a big advantage over the heavy arms when kept in its standard format. The level of damping of course changes all this. This is not correct. The damping may ameliorate the amplitude of the resonant peak, and result in less bass boost, but the high mass still provides an inertia, a resistance that the cartridge has to work against to track the groove, particularly on eccentric records. It is this inertia that causes the cantilever to flex and increase distortion. |
05-14-13: Richardkrebs
The cartridge still has to push this mass sideways. Either a relatively low mass with the ET2 or heavier with a Rockport , Kuzma, Walker or Krebs arms. In an undamped system with a fixed counterweight we see a large rise in amplitude at resonance. This is easy to control with damping. The adding of lead mass will increase distortion due to the higher inertia of the arm. Basically you have added a peak resonance in the bass, then tried to tame it by adding damping. Both the added mass and fluid damping will increase inertia, and compromise the ability of the cartridge to track the grooves accurately. On an eccentric record this will be even worse. The Krebs arm has some 65g of horizontal effective mass added - an increase of inertia close to 300%. This increases cantilver flex and distortion as per Bruce Thigpens commentary. 05-14-13: Richardkrebs
With a stiff cartridge; the only way to get Fr low enough to avoid interaction with audio frequencies was to make the arm heavier. The Fr of my arm/cart is 5.2 Hz. This is not true. Most tonearm designers target a FR of around 8-12hz. This is based on an assumption that most systems dont produce much response below 20hz and footfalls are in the zone of around 2-3hz, dangerously close to your 5hz. Secondly, the increased distortion from the added inertia of the arm resulting from the increased horizontal effective mass certainly impacts the audio frequencies. The phase anomalies from the increased distortion on the cantilever can be heard quite clearly in a system that is reasonably transparent and quick. Furthermore the peak resonance at 2-5hz that you quote can invoke instability in tracking, its the same as walking past a turntable on loose floorboards. 05-14-13: Richardkrebs
In past I have damped the resonant peak by adjusting the air pressure and deliberately dressing the lead out wires to damp horizontal movement. This method is fussy and not particularly robust. Basically what you are saying here is that you like the sound of the ET2 with additional drag inhibiting the free movement of the arm to track the grooves. In my experience this slugs the sound. Other users have found improvements by removing this drag - they have removed their fluid damping and replaced it with electromagnetic damping which has the benefit of not inhibiting movement until the movement happens. 05-14-13: Richardkrebs
My counterweight is 32 grams.
I have added 30 grams of lead inside the spindle in the center of working travel, such that it does not leave the bearing sleeve when tracking modulated grooves.
The ET2 can be optioned with the heavier magnesium wand. 8 gms heavier.
It comes with up to 40 gms of counterweight. 8 gms heavier.
In terms of bearing load carrying capability I have added 30 gm to a lightly configured ET2. If we option it with the magnesium and use all the supplied weights my weight adder is now reduced to 14 grams. Your mathematics is incorrect : The bearing spindle without arm/counterweight is 14g The aluminium arm is 11g The CF arm is 17g The Magnesium arm is 19g So the total horizontal effective mass of your 9gm cartridge on a standard ET2 arm with a 32gm decoupled counterweight is: 9g(cart)+11g(arm)+14g(bearing spindle)=34gm The total horizontal effective mass of your 9gm cartridge on your altered ET2 "Krebs arm" with 30g of lead added and the 32gm counterweight coupled is: 9g(cart)+11g(arm)+14g(bearing spindle)+30g(lead that you added to the spindle)+32g(counterweight that the cartridge now sees because you removed the decoupling)=96g Therefore you have increased the horizontal effective mass from 34gm to 96gm, an increase of 62g. I cannot see how you get to 6gm in your maths. Coupling the 32g counterweight adds 32g to the horizontal effective mass. Adding 30g of lead to the spindle increases the horizontal mass by 30g, even when placed inside the bearing. 05-14-13: Richardkrebs
If we option it with the magnesium and use all the supplied weights my weight adder is now reduced to 14 grams. This is another area where the underlying assumptions are misunderstood. Bruce's recommendations documented in the ET2 manual on low compliance cartridges is carry as little weight as possible as far out on the I Beam as possible. This keeps the horizontal effective mass low but increases the vertical effective mass. It is not recommended to load the I Beam with all the counterweights if one can shift the counterweights further out. |
Hi Rugyboogie,
Can the moving assembly on the Airline be taken out easily? If it can, and it is not too much trouble, I would really appreciate if you could weight it to confirm whether it is really only around 100g.
Hi Ct,
Yes, I still don't understand why the ET bearing feels smoother (to the hand) as compared to the Rockport when both are having the air-supply. I would assume both of them are virtually friction free under this condition! Maybe Rugyboogie can share with us his finding when he got his ET! |
Chris
The statement about the ET2 bearing was in relation to it being subject to the same rules regarding resonance , load carrying capability dynamic stiffness etc.
Any problems due to higher mass will manifest themselves in linear air bearing designs regardless of the manufacturer. There may be variations in degree, but they will be there.
In other words if my heavy ET has problems with cantilever flex, bass boost, phase shift and so on; so do the other heavy arms. Rockport, Walker, Kuzma. This because the horizontal effective mass is solely determined by the total weight that is moved sideways at the frequency of interest, since all of these designs are virtually frictionless.
The level of damping of course changes all this. Enter the oil trough.
The difference observed between the ET2 and the Rockport could be due to the designed operating pressure and the bearing clearance. Haven't seen a Rockport in person so this is a guess. |
If the air is off on my Kuzma Airline it is quite hard to move the tonearm.
Will be joining the ET owners club.
The ET arm that I purchased should be in my sweaty hands by the end of the week. |
Richardkrebs- There is nothing particularly unique about the ET2 bearing. Richard – what is this statement based on? Please note this observation from Thekong who has compared it to the Rockport. 03-13-13: Thekong
Hi Ct,
However, there is one interesting point that I still can’t understand. When moving the arm in and out by hand, the feeling of the ET is smoother (or I should say requires less force) than the Rockport! While I don't have the spec. of the 2 bearings, I have always assumed that the Rockport has a tighter tolerance / air gap. This can be shown when trying to move the arms without the air supply. While you can still move the ET quite easily, a lot more force is required for the Rockport in this condition. |
Richardkrebs - For a good discussion on this see CT0517's post on 01-12-12
Open the attachment and read pages 18-19 and 24-26. The graph on page 25 shows how this peak is completely removed by adding an oil through. ET2 damping trough Bruce why didn’t you number the pages ?!!! |
The horizontal effective mass for a linear air bearing arm is the sum of the mass of the bits that move sideways.
The ET2 reduces this mass by decoupling the counterweight. We all clearly understand this design feature. The benefit of this approach is to reduce the amplitude of Fr
The bearing design makes no difference to the effective mass or the resultant Fr. There is nothing particularly unique about the ET2 bearing. The cartridge still has to push this mass sideways. Either a relatively low mass with the ET2 or heavier with a Rockport , Kuzma, Walker or Krebs arms. In an undamped system with a fixed counterweight we see a large rise in amplitude at resonance. This is easy to control with damping. For a good discussion on this see CT0517's post on 01-12-12
Open the attachment and read pages 18-19 and 24-26.
The graph on page 25 shows how this peak is completely removed by adding an oil through. The subsonic peak has gone and provided Fr is low enough, so has its effect on the audio spectrum. In this paper Bruce talks about the effect being noticeable at 3x Fr. Way back in this thread I talked about the effect of resonance being present at up to 6x Fr. We use this safety factor in our designs in my business.
It is this effect that led me to fix the counterweight. With a stiff cartridge; the only way to get Fr low enough to avoid interaction with audio frequencies was to make the arm heavier. The Fr of my arm/cart is 5.2 Hz. Thekong's setup is a little under 5hz. In Fremer's review of the Kuzma he set it up with a Fr of 5 hz. This is no coincidence , we all set up our systems with effectively the same Fr, safely 4x below the audio spectrum. My point is that the Fr needs to be around 5-6 hz. To avoid this interaction. With a high compliance cart this target is achievable with a standard ET2, it cannot be achieved with a low compliance cart. At least 3 respected designers agree with me.
In past I have damped the resonant peak by adjusting the air pressure and deliberately dressing the lead out wires to damp horizontal movement. This method is fussy and not particularly robust. Adding the oil trough has solved these problems and allowed me to push the pressure back up. 17 psi seems optimum in my rig.
There have been concerns raised about the extra weight I have added pushing the bearing outside it's design spec.
I am using the original wand less its heat shrink wrap plus a lead headshell insert. Say the same weight. I am using an aluminum goose neck which eliminates one cap screw and the short lifter arm. I have also eliminated the male wiring plug and used a lighter grub screw instead of a cap screw for the gooseneck wand clamp. Say same weight.
I have fixed the counterweight and eliminated the I beam the brass threaded weight, several cap screws and the locking slider assembly. Say same weight.
My counterweight is 32 grams.
I have added 30 grams of lead inside the spindle in the center of working travel, such that it does not leave the bearing sleeve when tracking modulated grooves.
The ET2 can be optioned with the heavier magnesium wand. 8 gms heavier.
It comes with up to 40 gms of counterweight. 8 gms heavier.
In terms of bearing load carrying capability I have added 30 gm to a lightly configured ET2. If we option it with the magnesium and use all the supplied weights my weight adder is now reduced to 14 grams.
I use a Shelter Harmony at 9 grams. There are cartridges in the 16-17 gm range. If one of these was used the my weight adder shrinks to around 6 gms. It would be inconceivable that Bruce would design a bearing that could not take this small additional weight. |
05-13-13: Richardkrebs
Thekong.
It should be no surprise that the arm weighs in at that figure or even higher with the heavier counterweights. It is neccessary for it to perform well with low compliance carts. This is not correct with respect to the ET2. In my experience adding mass to the ET2 with low compliance cartridges reduces the speed, articulation, transparency and harmonic structure of the music. Increasing mass with the ET2 also increases tracking distortion and can result in a bass hump of 6-12db by loading up the cartridge with high mass. A quote direct from Bruce Thigpen Bruce Thigpen
If the weight is coupled the system resonant frequency would be extremely low, a resonant frequency at 3Hz with a significant rise in response (6-12dB) results, which would affect tracking slightly because of the asymmetric position of the cantilever, we opt for splitting the horizontal resonance frequency into two points and lowering the "Q" which improves tracking.
More important than tracking, the intent was to reduce the modulation effects of low frequency energy (FM and AM) that increase distortion in the cartridge Quote from ET2 Manual – Bruce Thigpen P29
It is desirable in most cases ( low to medium compliance cartridges 5x10 dynes/cm – 20x10 dynes/cm ) to use the minimum number of weights, far out on the cantilever stem. This decreases the horizontal inertia of the tonearm while increasing its vertical inertia. Adding mass to the ET2 increases the inertia to lateral movement and on eccentric records will result in increased cantilever flex and distortion. 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. This is what Bruce Thigpen is saying. Furthermore, with higher mass, once the arm starts moving, the lateral movement is undamped. Cartridge overshoot and uncontrolled cantilever flex are inevitable. This explains why when Richardkrebs added fluid damping the sound appeared to be better controlled or in his words had “greater presence and focus”. This is because the addition of lead mass and removal of the decoupling mechanism from the I Beam in his ET2 pushes the horizontal mass too high and the cartridge cantilever motion goes out of control. He would be better off reducing the horizontal effective mass by removing the lead he added to his arm and putting back the decoupling in the I Beam that he removed. If you go to the Eminent Technology website and read the ET1 manual (that’s the arm that precedes the ET2) you will discover that the ET2 was a design decision to move away from the high mass/fixed counterweight model utilized in the design of the ET1 to the low mass decoupled counterweight model utilized in the ET2. These new design considerations embodied in the ET2 resulted in substantive improvements in the quality of sound reproduction. The decoupled I-beam methodology employed by Bruce Thigpen in the ET2 is designed to minimize horizontal mass and ensure that the resonance of the I-beam and counterweight remains below the horizontal resonance of the arm so that the 2 resonances (arm and beam) do not couple together to produce a large peak resonance in the bass. |
Thekong.
It should be no surprise that the arm weighs in at that figure or even higher with the heavier counterweights. It is neccessary for it to perform well with low compliance carts. This provided that appropriate damping is applied. Lead out wires, air tube, and maybe an oil trough.
An obsessive designer like Andy Payor would have taken this weight factor into consideration.
I agree, it would seem that the Kuzma is indeed a lot heavier, based on its appearance. That said, maybe it uses carbon fibre and other weight saving techniques? |
Manitunc – just a note on my last post. If it works its the original ET2 manifold. If it needs a higher pressure to work you have a HP manifold. If we are talking about an older ET2 arm it may need more pressure because of it being dirty. Its a good idea to clean inside the manifold first. Slide out the spindle and use a toothbrush with alcohol and scrub the inside of the manifold. See page 40 of manual. This is an easy enough procedure and highly recommended for anyone buying a used ET2 with no history. Cheers |
05-13-13: Manitunc
Is there a way to tell if I have a high pressure manifold on my ET2? Some sort of marking on the manifold, or a different size? I have a couple of different pumps, but dont want to put on a higher pressure if its going to damage something. Hi Manitunc *********************************************** ET 2.0 spindle is about 5/8 inch. ET 2.5 spindle is about ¾ inch. ************************************************ from my 05/03/2013 post. One way to tell if its a HP manifold. So there are many ET2’s out there that have manifolds set up for really high pressures. These were custom ordered. If you want to know if you have a high pressure manifold or not. Push it out – inscribed on it will be XHP or HP. The other method is to hook it up to a compressor and start adding in PSI and see what it can take. If it came with a WISA is was meant for 5-7 psi. The original pump was in the 3 3.5 psi range. Another way to tell. Bruce built the manifolds for different pressures based on customer specs. If somebody bought their ET2 or ET 2.5 used and did not know the seller they don’t know what the pressure is – unless it came with the pump. In order for the air bearing to become rigid it needs to be run at least at the PSI designed by Bruce for that specific manifold. Going over that pressure may produce sonic benefits in a persons room – IMO - this is subjective thing; based on our own room/gear synergies - just like speaker wire and interconnects – hah hah. How do you like that comment ? if a higher pressure works - great. The original ET2’s were around 3 - 3.5 psi with the Takatsuki SPP-6GA pump. The WISA pumps were 5-7 psi. So Manitunc I suggest you try your arm first with the original low pressure pump first if you have it – SPP-6GA. If it works its the original ET2 manifold. If it needs a higher pressure to work you have a HP manifold. This applies to both ET 2.0 and ET 2.5’s. This can be confirmed by contacting BT. You can’t hurt it with higher PSI – in fact raising the pressure in increments will let you fix any leaks your arm may have if it has been sitting around for 10 years. You will blow off the air hose if anything. Since we are talking about pumps - I will post how I test my ET2 pumps. Cheers |
Is there a way to tell if I have a high pressure manifold on my ET2? Some sort of marking on the manifold, or a different size? I have a couple of different pumps, but dont want to put on a higher pressure if its going to damage something |
I have measured the weight of the Rockport 6000 in the weekend, and to my surprise, the whole moving assembly weighted in at 90g (including the A90 at 8g, and a spacer at 2.5g). I am using the lightest counterweight out of the 4, and the heaviest one would add another 15g!
With the figure about, it is hard to believe the moving mass of the Airline is only around 100g considering how massive it is compared to the 6000! |
Hi Richard,
Yes, the 6000, and all other Rockport arms, has damping trough. The “paddle” is fixed, so unlike the Walker, you have to adjust the amount of damping oil you put in!
However, I and a couple of my friends who had the 6000, prefer it without damping; it just sounds more lively, or more PRAT! I may revisit this topic later! |
Thekong ....the owner of that Sirius III was complaining on Audiogon that the arm couldn’t track more than 3 cuts into the LP..... Hi Thekong – thx for that info. Well imo whatever it was able to play ...it would have been a subpar performance from the start of the first track anyway from what is capable. Hopefully the wires have since been fixed up. What I don’t get...how does a high profile, statement item like that get into that condition; especially when the wires and also the air tubing in this case represent an Achilles Heel if not set up properly. Not a question per say just a little dis-belief on my part considering the dollars involved. Cheers |
Thekong.
It will be interesting to read about your findings.
Do you have the horizontal effective mass figure for the 6000? Can you please post this if you have it.
My experience with adding weight is that you should be targeting a horiz resonance of 5-6 hz. The formula on the ET site can be used to calculate this and hence how much weight to add. You may need to concurrently adjust the vert mass as well. This I did with the lead shim inside the headshell.
From the photo you posted, it looks like the 6000 has a damping trough? Until recently I have been using the dressing of the lead out wires for damping. This works but goes out all the time, requiring constant tweeking. The oil trough is much better, being consistent and I would now consider it to be manditory in a heavy arm.
thanks |
Ct,
You have sharp eyes, yes the owner of that Sirius III was complaining on Audiogon that the arm couldn’t track more than 3 cuts into the LP. There are actually 2 black hosts in that photo, one for the air, and one for the signal wire. I believe it was just set up wrongly; it should be like the photo of the 6000, with the signal wire host pull back as much as possible, and both the air-host and signal wire arranged into a hanging n shape!
Dover,
My 6000 came with 4 counterweights of different sizes to match with different cartridges!
Regarding the off-centered cantilever of the VDH, I believe, while great sounding, it is just a very fragile design, and probably not really fit for air-bearing arm including the ET2. After having it fixed, my friend has used it on both the SME V and Graham Phantom with no problem!
I will try to weight the sliding assemble of the 6000 this weekend and report back! |
Thanks for that info Thekong and Dover.
Thekong – something doesn’t look right to me with that Sirius III pic ?
Looking at the air tube wiring – how does that tonearm get past the 2nd track?
Isn’t the air tube pushing back at the arm as it makes its way across ? Is there that much friction in the slider to not be affected?
If that was an ET2 just the wires alone in that position would cause it not to work. Sorry for all the questions.
Definitely a very different design. Thanks for the pics.
So the air that comes into the arm is going into to a smaller diameter air tube. This is compressing the air and I assume making higher pressure.
Cheers |
The kong,
thanks, pictures are interesting - the stiffness around the arm connection is obvious. The 6000 does look quite flimsy, whereas the Sirius has a tapered armtube to a larger armtube clamp. The energy control should be much better.
Also interesting are the similarities to the ET - the tapered armtube for MC's and the use of a relatively small counterweight quite a long way away from the bearing. Having less mass in the counterweight further out lowers the horizontal effective mass ( clearly a design goal for Payor ) but increases the vertical effective mass ( good for low compliance MC's ). This is exactly the same strategy employed in the ET.
Re the van den hul bent cantilever - I ran a Shure V15Vmr on the ET2 for about 10 years whilst I had a hiatus from audio in the 90's. The Shure is around 20 yrs old, still has the original cantilever & stylus, has only ever been used on the ET2 and the cantilever is as straight as a die; this I think a testament to the ET2's relative light mass and decoupled cantilever and of course the electromagnetic damping discussed earlier in this thread would have helped as well. |
The 6000's relatively low vertical effective mass put its resonant frequency above the ideal 8-12Hz region with moving-coil cartridges of average weight and typically low compliance, causing the bass to begin rolling off prematurely. Andy Payor solved the problem on the System III Sirius arm—see my analogsourcereviews/review in August 2000—by adjusting the mass so that the arm's fundamental resonant frequency would be compatible with a wider range of cartridges. Hi Dover, Thank you for taking the time to check! The above is a quote of MF from his review of the Kuzma Airline. By “adjusting the mass”, I am sure he meant “adding the mass”! Both the 6000 and 7000 also used carbon-fiber armtubes, but not as sophisticated as the one on the Sirius III. But then, I agree with you that the weight increase of the armtube would definitely be less than 10g, and most likely in the 3-5g range. Actually, by looking at the photos alone, it is hard to believe the massive armtube clamping system on the Sirius III has the same weight as that on the 6000. But, I have no reason to doubt AP’s claim! Sirius III6000Hi Ct, While I don’t have any really high compliance MM cartridges, I have no problem, “sound wise”, matching the 6000 to the relatively high compliance VDH Colibri! Yes, the combo is relatively lean in the bass/mid bass, but I consider it the character of the cartridge. Now, I say “sound wise”, because while the sound was fine, I (and also my friend who had the same combo) found the Colibri’s cantilever slightly off-centered after a period of time. This I took it as the fragile nature of the Colibri’s design. MF repeatedly stated the 6000 was relatively bass shy compared to the Sirius III and Kuzma Airline; I believe a major reason was that the stock pump just couldn’t supply enough pressure. As I mentioned before, I believe the 6000, 7000 and Sirius III shared the same bearing, but the 6000’s stock pump (probably due to cost constrains) could only supply a max pressure of around 11 psi, and without any surge tank. Once I upgraded it to a June Air compressor with integral surge tank, plus additional pressure regulators, supplying 34psi to the 6000, its bass weight and definition improved considerably! As I understand from the Rockport agent, the Sirius III’s arm also uses around 32-35 psi! |
Ct0517 - We know the heavier ET2 armtube affects the horizontal mass as well. this was worded badly. This thread is too old to allow for corrections. I wanted to say the arm wand weight lighter or heavier, affects both the vertical and horizontal inertia at the same time. This is really important. |
Thekong - In the later, upgraded, models of the Rockport 6000, i.e. the 7000 and the arm on the Sirius III, AP chose to use heavier armtubes. I believe all 3 arms used the same air-bearing, and their armtube clamping systems are of the same (or very similar) total weight, but the clamping system on the Sirius III are said to be 20 times stiffer due to the improved design.
....Granted, AP might have added the weight to help (add) more in the vertical, rather than the horizontal, moving mass, for better matching with mid/low compliance cartridges, but added weight he did! That may just be a matter of compromise! Thekong - thanks for sharing this info. Are you able play high compliance cartridges on your Rockport arm ? We know the heavier ET2 armtube affects the horizontal mass as well. but the clamping system on the Sirius III are said to be 20 times stiffer due to the improved design. I am assuming that this would limit the type of cartridges the Rockport Sirius III tonearm can now play as far as compliance is concerned ? Cheers |
Richard re: damping trough. Thanks for bringing this up. I have completed my game of musical turntables, so I will revisit the damping trough now. It can get messy when moving an ET2 from one TT to the next with a trough of oil attached ! My main TT is completely changed from the last time I used the fluid so will try it again. The fluid that Bruce uses in the trough is 8000 centistoke silicone fluid. I ordered some today from him along with the adhesive. Will post impressions later. Richardkrebs - My apologies in advance if this topic has already been covered in the thread. Too many posts to read thru. Richard - This thread is unfolding like a book. Very relevant ET2 information was discussed early on and throughout. I encourage a read through. If for no other reason than to understand and gain insight into why some members made the decisions they did. Cheers http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1325551242&openflup&67&4#67 |
The kong, I am on a project at the moment and cant get back to the article but I believe it was a direct quote..I can confirm later if you like. Meanwhile I see in the stereophile review of the Sirius arm: August 2000 The Sirius tonearm tube should be virtually inert, made of a constrained-layer-damped, 8-ply sandwich of carbon fiber and epoxy composite: four layers on each side of the damping material. Inside is a second tapered carbon-fiber tube, the space between the two filled with yet another damping material. The materials, construction, and aerospace pressure-laminating techniques create an armtube said to have the stiffness of steel, yet weighing only half as much as a comparable aluminum tube.
Another single billet of aluminum alloy is machined to make the bearing mount, tonearm clamp, and counterweight assembly. This is a big improvement over the design of the Series 6000 arm: the structure is said to be 20 times stiffer than before, yet no heavier. This suggests the armtube is more rigid in the later models but lighter. Fremer also paraphrases Payors comments on the ET as follows: The air-bearing scheme—comprising a stationary bearing and a moving rail—invented by Eminent Technology's Bruce Thigpen and used on his tonearm as well as on the Maplenoll and Walker Audio turntables, comes closer to being truly "linear" because the bearing can be more highly pressurized. But the rail's large horizontal moving mass creates another set of problems. And a true linear tracker completely eliminates a pivoted arm's inherent tracking error and skating-force vectors.
All of which, to Payor, means that his arm is the best currently available, and the true state of the art.This is extremely important, as low moving mass is critical to the performance of a linear-tracking arm. The use of English can be deceptive - large, heavy, higher mass. We see that Thigpens "heavy" armtube is only 2 gm higher. Payor may be referring to the physically large area of the arm/bearing tube or he may be referring to the actual mass, but it seems clear to me that he favours minimising the horizontal mass. Furthermore, if you read the full article you will see that the bearing design and parameters and moving masses involved are mutually dependent as they are on all airbearing tonearms. I dont believe you can convert a Kuzma to a low mass or an ET2 to a high mass arm without redesigning the air bearing. The resonances of the bearing itself can end up in conflict with the resonances generated by the arm/cartridge compliance. This is where Richardkrebs continues to get the maths and physics wrong; there are multiple resonances involved, and the multiple resonances can quickly accumulate when overlapping - they are not a single spike at one frequency. This is what is happening with the ET2 when Bruce measures a 6-12db lift in the bass when coupling the counterweight - which effectively doubles the horizontal effective mass. |
Andy Payor and Bruce Thigpen both disagree with adding mass. Hi Dover, Regarding the passage you quoted Andy Payor from Michael Fremer’s review on the Rockport 6000, while I have never read that review, but reading MF’s later reviews on the Rockport Sirius III and Kuzma Airline, gave me the impression that those comment were from MF himself rather than AP. Of course, AP might very well agree with that! Can you confirm? About AP’s disagreement with adding mass, I would like to share some information. In the later, upgraded, models of the Rockport 6000, i.e. the 7000 and the arm on the Sirius III, AP chose to use heavier armtubes. I believe all 3 arms used the same air-bearing, and their armtube clamping systems are of the same (or very similar) total weight, but the clamping system on the Sirius III are said to be 20 times stiffer due to the improved design. The heavier tapered armtubes (so the heavier moving assembly) on the later arms are said to be there for better bass performance, and minimize resonance. Granted, AP might have added the weight to help (add) more in the vertical, rather than the horizontal, moving mass, for better matching with mid/low compliance cartridges, but added weight he did! That may just be a matter of compromise! |
My apologies in advance if this topic has already been covered in the thread. Too many posts to read thru.
Twenty years ago I made a oil damping trough for the then standard ET2, mounted on a Goldmund Studio. Mixed results, which could have been as much to do with opening the window to the performance of the Studio, as anything else. I put it in storage and forgot about it, only to find it again recently when looking for the aluminium goose neck for Chris.
So installed it on the current arm. Nice changes to the blackness of the background. The system is even quieter. As a result, it doesn't seem to extend dynamics upwards but downwards further into the low level detail. A very agreeable effect. Also greater presence and focus. It will be staying.
Is anyone else using an oil trough? If so what are your findings? I see from the ET website, that a very elegant design is offered.
bdpses |
Dover ....but there are some pivoted arms that can provide musical enjoyment as well. You’re a real funny guy Dover. Did anybody ever tell you that? I did not say I didn’t enjoy my pivot arms. I said they couldn’t go straight.....they need some help. A couple of questions. What make of pump and PSI did you use with your ET2, and did it (the pump) produce resonances and vibrations that forced you to use/build an external surge tank? How long ago was it setup in your room? |
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. |
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.htmlthats 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. 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. There are many around. My ET2 HP based on the notes that came with it (it was bought used) is a 50 psi manifold model. My ET 2.5 manifold was custom made for 19 psi by Bruce for me based on my requirements. Why 19 psi ? this is covered on the first couple pages of this thread. So there are many ET2’s out there that have manifolds set up for really high pressures. These were custom ordered. If you want to know if you have a high pressure manifold or not. Push it out – inscribed on it will be XHP or HP. The other method is to hook it up to a compressor and start adding in PSI and see what it can take. If it came with a WISA is was meant for 5-7 psi. The original pump was in the 3 3.5 psi range. imo - There are three different areas being discussed here and they really should he kept separate to avoid confusion. 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. 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. 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. 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? Cheers |
