Eminent Technology ET-2 Tonearm Owners

Frogman.
Excellent! You have inspired me to do this with mine.
Thanks for the feedback.

Ketchup and Frogman.

Thanks for the pics.
Can either of you describe the changes with the wire outside. I would expect a more lively, detailed, precise presentation.

Seeing the manifold like that reminded me of the shim/grub screw set up. Has any one made any progress on this?

Thekong.

The answer to your question regarding frequencies impacted by horizontal Fr is shown in the attached graph.
From memory your Horiziontal Fr was around 5hz with the A-90. So substitute 5 for 1 on the x axis and scale up from there. At 15 Hz (3) the rise in response is almost zero. This is what BT was talking about when he mentions 3xFr.

It could be that the perceived improvement in bass performance of subsequent Rockport arms has more to do with the wand, gooseneck and counterweight arm stiffness, rather than total weight.

Different bearings make virtually no difference to this graph since it is the mass that the cartridge has to push sideways that counts.

The flavour of different arm bearings, however, is another matter entirely.

The various curves are showing different values of Q (damping) Note the level of damping makes virtually no difference at frequencies of 3x Fr and above.
This does not mean that we can ignore the amplitude at resonance, since it is shaking the arm and this has an impact in the audio spectrum. FM and AM modulation.
Bruce reduces this amplitude by decoupling the counterweight. It is an elegant, brilliant solution. Others damp the resonance as I have done. The oil trough, way less elegant, is also a very effective way of doing this.
Both methods reduce FM and AM artefacts.


http://s1173.photobucket.com/user/CT-993/media/ResonanceGraph_zpsdd78e0f4.png.html?sort=2&o=7

What this means, as Spock15 says, at 3xFr and above the arm appears to be solid to the cartridge. We want the cantilever to move not the arm.

Now look at frequencies below Fr. At say 0.25 Fr we get transmissibility of 1. What this means is that, with the compliance of the cartridge used, the whole arm moves sideways. The cantilever does not deflect. This is important for eccentric record issues. In other words stay above a horizontal Fr of 3hz. (4x 0.75hz) ) 0.75 Hz being the frequency seen with an eccentric record ay 45rpm.
Putting this another way. BT uses at 30cu cartridge in his manual to calculate horizontal Fr. The arm weight he uses is 30gm plus 7gm for the cartridge. We have to assume that he is ok with this combination and that he is not worried about cantilever deflection on eccentric records. When using a 10cu cartridge we can increase the horizontal mass of the arm to 111 gm and have the same peace of mind about cantilever deflection with eccentric records. The cartridge is 3x stiffer so we can push around 3x the weight. It is that simple. Forces on the record groove wall are another thing. We use a stiff cartridge this is the price we pay. Don't play heavily eccentric records.

Ha_ha_he_man.

What I hear with a heavy linear arm is this... The music takes on mass. Individual notes are solid. This is not to be confused with "heavy" in the derogatory sense. A live struck triangle has this mass. One can imagine walking up to the sound of it and holding it. It would have mass and a textured surface. This is very hard to reproduce and I do not hear this effect with light linear arms when carrying low compliance cartridges.

Dover
" self taught engineering school of fabulosity."

You go too far....

I have a tertiary education in engineering. I hold an aircraft avionics qualification and a radio technicians certificate. I teach hydraulics and electronics to paying clients.

My company employs 52 people across two countries.
We specialize in the design and building of complex servo electro hydraulics.
Recent projects have been damper doors for jet engine power stations in Oman and Iraq.
These doors, 7 meters square, are required to swing thru a 90.degree arc and stop precisely in position. Fractions of a mm are possible. The doors need to do this at both high, emergency close speeds and normal slow rates. With the multi mega watt engine buffeting it with an air stream just below supersonic.
Get the Q wrong with something as massive as this and it either fails to reach the go to point in time or it shakes itself to destruction. We usually target just below critically damped to give added safety.
My public liability does not cover destroying a multi billion power station.
I understand resonance, Q, time constants, mass damping et el.
The survival of my company and potentially the power station workers and my staff depends upon it.
You cannot begin to imagine the pre qualification process a company has to go thru to be even considered to quote on projects like this.
Compared to design work like this, a tonearm is relatively mundane. Certainly a whole lot less stressful.
I know how the ET2 works.

Double posts and thread ghosts of the past. How does that happen?

Chris.
It is good to see that analogue gear is holding its price. Maybe the current trend of interest will continue. My sons and their friends are keen to spin records. A welcome change away from the broken washing machine music one usually hears leaking out of their ear buds.

Lets look at things again.
I am officially retracting my retraction to Thekong regarding the ET2.5. Here is why.
When I realised my obvious mistake in thinking he was going to place a rigid CW arm on an ET2, when in fact he was proposing to use one on an ET2.5, I looked at the figures for this arm.
On 03/14/13 Chris posted the Horizontal resonant frequencies for the two arms. ET2 5-6hz ET2.5 2-3hz.
I already knew the horiz mass of the ET2, so calculated the mass of the ET2.5 assuming the same cartridge mass and compliance was used for both arms( a reasonable asumption)
Res freq is proportional to the square root of the inverse of the mass. In other words 4x mass = 1/2 res freq. Since the ET2.5 freq range was approx 1/2 the ET2, it implied that the ET2.5 was 4 x heavier, making it over 100 gm. This surprised me but in the absence of any other information, I took it on face value.
From experience it would be problematic if Thekong were to add a rigid weight to this apparently already heavy arm. Later on in the thread, 03/14/13, Chris published the actual weight of the ET2.5 being only 8gms heavier than the ET2. This means that ET did not use the same cart parameters when giving Chris the original info. Thekong, your call obviously but if I were you I would try a fixed CW arm provided it is really rigid.

Re my question re interaction between the two spring rates, cart and CW. I raised this question, not because I had suddenly "understood" how the ET2 worked but because the idea that having two springs driving the same structure could actually have a down side. I started thinking about this when Dover commented on the superior transient performance of his unipivot. The idea further coalessed when the tests were done with loosening the CW arm bolts. This would change the Q and possibly the res frequency of the CW assembly. Potentially reducing any interaction between the two springs, but not eliminating it.
When I fixed the CW and added further mass and used a low compliance cart, there was an unexplained positive side effect. Focus and sharpness improved. Transients were better. It was some years ago when I made this change and while liking the improvement, I didn't put too much thought into 'why'. While I did not post these positive results. My question to the fellow posters was " could the interaction between these two springs be a problem." I don't know, but it is a valid question and the graph I posted suggests that they do "talk" to eachother. My thinking was that there may be a link between the transient improvements I acheived and the use of a swinging CW.

When I first purchased the ET2, I set it up as per the manual, to the point of obsession. As with all of my gear, I wanted to extract every tiny bit of performance. In standard from, it was best as per manual, with the slight adjustment of swinging the Ibeam down as Chris has posted.
Years later I started to experiment. The result is what I have now. It is just my opinion, no more or less valid than anyone else, but I believe that it is significantly better than a standard ET2, when using low compliance carts.

We can debate this from first principles all we like, but the proof of the pudding is in the hearing. What does it sound like, how does it perform? This is evaluated with our ears.

I will not be degrading my arm by converting it back to standard form.

Chris,
This is strange.
For the example BT uses in the manual, pages 48 and 49. The res freq for the ET2 with a 30cu cart we get around 4.7 hz.
For the ET2.5, assuming it is only 9 gms heavier the res freq with the same cart would drop to around 4.2 hz

Perhaps BT could clarify this?

Thanks .

Maths and Physics.

A few days back I wrote that the res freq of the arm was proportional to the square root of the inverse of the mass and stated that there was a discrepency in the ET2/2.5 comparitive figures that Chris had posted. This because the figures showed a halving of resonant frequency for the ET2.5. I speculated that this meant that the two sets of figures must have been taken under different circumstances. Chris followed up my post up with a question to BT where Bruce appeared to say that no, the measurement conditions were the same.
This did not make sense and was contrary to resonance theory. Since I did not know the actual question Chris asked Bruce, I decided to contact Bruce myself for clarification. Below is my question and Bruce's answer.
Note Bruce uses the phrase "everything else is the same". This could be where the confusion came from.



On 4/18/2013 10:22 PM, Richard Krebs wrote:
> Bruce.
> Good day to you..
>
> My question concerns the horizontal resonant frequencies of the ET2
> and ET2.5 Chris spoke to you about this some time ago and you gave him
> a range of frequencies 5-6 hz for the 2 and 2-3 hz for the 2.5. Chris posted your info on the ET2 audiogon thread. The range of frequencies for the ET2 was approx double the ET2.5 This is confusing if the same wand, cartridge weight and compliance was used for both arms, as it implies the the ET2.5 is around 4 times heavier in the horizontal plane.
>
>
> For a 8 gm cartridge of 30 cu I get horizontal resonance figures of around 4.7 hz and 4.2 hz for the ET2 and ET 2.5 respectively.
> Are my figures correct? If not where am I going wrong?
>
>
> Many thanks .
>
> Richard.
>
>

Richard,

Your figures are correct and closer to reality. The only difference in mass is in the spindle, everything else is the same. The spindle adds about 10 grams to the horizontal inertia figure and almost nothing to the vertical inertia. I hope this helps.

brucet

As you can see Bruce has confirmed my figures are correct and the resonant frequency of the ET2.5, for the same cartridge, is not half that of the ET2, but only slightly less, exactly as I calculated.
If any one wants to confirm this for themselves, they need only go to the horizontal frequency formula in the ET2 manual. Choose a total mass (Mc plus Ma) of say 40 gm.(simulating an ET2). Insert the compliance figure for your chosen cartridge and calculate the res freq. Now recalculate with Mc plus Ma equal to 160 gm. You will get 1/2 the original number. Recalculate again with Mc plus Ma equal to 50 gm (simulating an ET2.5) you will now get a figure only slightly lower than the original.

So what can we conclude from this.

Someone who understands the math and physics around the ET2/2.5 would know that......
a)....it would be obvious, from a mile away, that the resonant frequency of the ET2.5 with the same cartridge would not be 1/2 that of the ET2.
b)....a heavy arm, when and only when, connected to a low compliance cartridge is a high performance, viable alternative
c)....the air bearing employed on these arms is effectively rigid at audio frequencies. So they should look elsewhere when looking for the cause of compromised note leading edge performance.

Chris.

Good to read your findings on the gooseneck. They parallel what I heard when making the change here. You can expect more of the same when we find a way to bypass the o'rings in the manifold, along with a satisfying jump in dynamic contrast and low level detail.

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

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

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?

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.

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.

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.

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.

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.

Chris.
Brilliant test idea you used for checking the smoothness of the pump air flow.
I smoked my current pump running it at a higher pressure. Will definately be trying your idea out when it's replacement arrives.

Dover.
- The error you repeat, is saying that my arm exhibits a rise in bass response of 6-12db. I'm pretty sure that most of the readers here would not call 5Hz bass. I can't hear that frequency and my system certainly cannot reproduce it. The arm has always had some method of damping. This reduces the amplitude of resonance at Fr. If you ask BT, he will say that the amplitude falls away to be benign at 3x Fr. Just over 15hz in my case. A frequency which some may call Bass, but one which I doubt my system can reach down to either.
-The change in shape of the resonance curve I refer to is clearly shown in the graph BT published with the oil trough manual. It is not a smooth standard deviation type curve. There are bumps and hollows on the slopes. This is caused by other structures resonating at frequencies near the fundamental.
-BT does not increase the horiz effective mass by 18gm when he adds his oil trough and nor do I with mine. He adds 18gm to the total weight of the arm. The effective mass is increased by the weight of the paddle. Well under 1 gram on mine. This makes my arm around 96 gm when carrying the Shelter, not 114 as you state.
You repeatedly try to paint the weight of my arm as being an outlier in linear arms and that my arm is singular in being so heavy. It is not, as we have seen in this thread. Some fellow posters own these heavier arms. Criticize my arm and you simultaenously criticize theirs.
-BT uses a very elegant method to reduce the FM and AM interfearance in the audio band caused by a high ampltude Fr. He decouples the counterweight which reduces the amplitude at Fr. Other designers use another method, they damp the arms horizontal movement which also significantly reduces the amplitude at Fr. This by using an oil trough, the lead out wires, the air line or a combination of these. It is simply another method of dealing with the problem. Both are valid, both have their advocates and detractors. This is the nature of our hobby.
-Chris has clearly enunciated the improvemmets in the bass articulation when he applied my goose neck design. Could it be that the problems you hear in the bass region when you locked the counterweight were simply due to the compliance of the gooseneck being laid bare, combined with maybe insufficient damping?

Dover says.
"....on an undamped standard ET with decoupled counterweight there is a resonant peak at 3 times the fundamental resonant frequency, and that this is reduced with fluid damping on a standard ET with decoupled counterweight."

I say.
"At 3x Fr the rise in response is almost zero."

In response to this question..

In the technical section you talk about phase shift beginning at 2 to 3 times the resonant frequency down to Fr.
Does this mean that there is a resonant peak at 3 x Fr or is this the point where the phase and response errors have reduced to low levels?

Bruce T says...
"This is the point where, above this frequency, the phase shift becomes minimal, as you approach the resonance frequency, the phase shift increases. I hope this helps, thank you very much."

brucet

Bruce uses the phrase "becomes minimal" I used the phrase "almost zero". Bruce and I are talking about the same phenomenon. Neither of us say it is zero because the curve is asymptotic to zero. It is this characteristic which causes designers in my industry to err on the side of caution and use 6xFr. A figure I have mentioned previously.

There is No resonant peak at 3x Fr. The amplitude and phase problems reduce the further we move above Fr. Exactly as shown on the transmissibility graph I posted, which is an accurate representation of what is happening with the arm at frequencies around Fr.

Ha_ha_he_man
Further to your request.

What I hear when making the counterweight arm solid with a suitably stiff structure and when using a low compliance cartridge is this...
The image is a little more focused. Individual elements within that image are a little more vivid.

I stress as Chris has quite corrctly pointed out, my arm is optomised for low compliance cartridges.
Further I now consider an oil trough to be manditory for this rig.

Chris and others.
I can see how our discussion has become tedious for other readers. I apologize for this and will be more considerate moving forward.

On a bit of a side path. What happens when a new better piece of gear is installed, say new speakers.
We set them up, friends come around and after they are run in, all listener's agree that it is a big improvement. We all hear better this and more of that,......for awhile. Then it becomes the new normal and we go on the quest again for "more". Has anyone else thought that this hobby of ours is an addiction?

BTW
When Goldilocks dipped her toe in the bath, she found the temperature to be just right.

Chris.
I have added a multi spring test to the long agenda of things to try.

Liked you cartoon. How true.

Many thanks

Slaw.
"Variations in the degree of trueness"
Totally agree. Since I had the luxury of building the arm and TT, almost concurrently, I could deal with these topics in real time.
Getting accurate alignment when two components are brought together from different manufacturers, without the ability to adjust, would be pure luck.

Slaw.

Wrong thread I know, but are you in a position to tell us about your "up coming tt project" ?

Chris.
Yes lifting off at record end is an interesting exercise after a few glases of fine NZ Pinot Gris.
Which end for the trough? The one with the least amount of joins and material changes before we get to the cartridge. In my most humble opinion :-)
Was it Townsend that put the paddle on the headshell itself?

Slaw
Yes the arm has considerable vta adjustment but it cannot easily be done while playing. Chris's post clearly shows the importance of correct vta.
This adjustment on the standard ET2 with the curved pillar is a brilliant design feature and one that is was unable to emulate with mine due to the machining capability I could access back then. MK2 will address this.
Other than the three wand positions, alignment adjustments are facilitated via the gooseneck like the original.

Here is a conundrum. Stylus drag is significant, being able to slow some TT platters. What effect does this force have on cartridge alignment?
Since the cantilever is angled down towards the record, any change in drag would tend to increase or decrease this angle.
Does this mean that the stylus is not only moving in the desired x and y axises but also in the z axis due to changes in drag, I.e modulation level and frequency?
It is amazing that we get anything that sounds like music off LPs. This given the myriad of compromises and the lack of industry standards

Another Pinot Gris I think.

Chris and Slaw. This whole geomerty thing is interesting.

This is how I understand it...if we set up a curved pillar in Slaw's "neutral zone" for a given record thickness, the arm will land the stylus at the same point on the LP for a range of VTA's, provided we always use the same thickness record. Change the record thickness and the stylus will land at a different place.
For a straight pillar, the stylus will land at the same point for different record thickness when setting the same VTA, but will move when we use a different VTA.
This could explain Slaw's need to adjust overhang for different thickness records.
So the choice is which feature do you want?

Chris. Speed accuracy, yes a Pandoras box.
Cheers.

Chris.

That is one serious looking wand.

Have you tried it yet? How does it perform compared to the AL version?

Thanks

Chris.
Quite a few of my customers use after market metal mats. SS and CU.
This adds considerably to the moment of inertia of the platter, but none have had any problems that I am aware of.
My own custom platter is the same weight but a slightly higher moment. Again no problems.

Slaw
I very much look forward to reading about your TT project.
As before I agree totally that things need to be true. If you are controlling the whole process and have access to a good machine shop, this should not be difficult.
My TT and Pre happen to sit on granite surface plates, surplus left overs from our machin shop. They are used, not of their flatness but their energy sinking properties.

If you are going to pod the arm, is it necessary to retain the standard arm/ plinth arrangement? Could you machine the arm pillar and pod as one piece? Some would argue that multiple paths to the plinth (pod) can be problematic. Maybe have the final adjustment of the arm's trueness set by the pods feet? Just a thought.

I have fused my custom arm pillar to the plinth with a solvent that actually melts the surface of the acrylic. The vendors of this stuff claim that the result is a homogenous material as strong as the parent. Thus the pillar and plinth are effectively one. I retained the ability to correct any dimensional errors since the whole plinth could be machined with the arm pillar attached.

I'm sure that your project is going to be a lot of fun and produce brilliant results.

Dover
Correction, you have not heard the full krebs upgrade.Two people in NZ have.
Please confine your comments in posts to those that are actually true.

In order to maintain standards and ensure authenticity, I have initiated the use of identification labels on my upgrade. Going forward, only TTs that meet these standards will be shipped with this authentication. Every TT done by Bill meets these standards. In contrast the 2 off MK2s done in NZ do not, being prototype mules 1 and 2, they were effectively a work in progress. Both of these owners are aware of this and are getting their units brought up to spec FOC. This developmental work has meant that any brand DD TT can now be upgraded with a high level of confidence, circumventing the prototype stage.
Baring imports, there is only one TT in NZ that meets my requirements, a MK3, and that is mine.

Back on subject, Chris, we are waiting to hear about the mag wand performance.

Chris.
When Bruce machines the wand, I assume that this is what happens...
The bore thing is basically drilling a hole to create the ID dimension. Sometimes the drill is rotated, some times the work piece (bar) is rotated. It depends upon the machining centre. For complex internal shapes it is possible to undercut the workpiece such that a larger ID is created say in the center section compared to the two ends of the resultant hole.
The turn process is like moving a chisel along the outside axis of the spinning bar to create the OD dimensions. The chisel can be moved in and out to create different ODs along the length of the bar.

I could send you a video of our milling machines running but you don't see a lot as the work piece is flooded in cutting fluid to keep it and the tools cool, lubricated and help with swarf removal.

The art in this process is getting the feed ( how fast you pass the cutting tool along the surface ) and speed rates ( how fast you spin the work piece or cutting tool ) optimized to produce the required tolerances and surface finish, in sync with the conflicting requirement of finished product thru put, tool wear, and machine loading.

Dover.
Please contact me via my website. There, I can answer your questions and any others you may have in detail.
Thank you for your interest in the upgrade.

Slaw.
It will be intersting to read about your TT project.
Re the arm pod and pillar, perhaps I have missunderstood?
If the arm pod has three adjustable feet it would be possible to replicate the effect of the three feet currently used by Bruce in the arm pillar. It would be easy enough to replicate the curved VTA arrangement of the pillar in a one piece pillar / pod. The three adjustable feet would need to employ finer threads on the screws to avoid them being too coarse in adjustment due to the longer fulcrum. Is this an option?

Agree with you on the acrylic thing. It can have the negative effects you describe. I think that a lot of this has to do with how it is used though. That said if/when I build another TT, I will almost certainly use a different plinth material. Probably durallium or austenetic cast iron.

I use discarded surface plates under the TT and Pre for their vibrational energy transmitting characteristic. They then sit on soft wood and sand which should dissipate this energy. Like you, the original TT and Arm made extensive use of other surface plates, during the build process, to ensure their trueness.

It is great to read about people taking the big step of commiting time and effort to a major project like yours.

Chris
Am I up and running?
Yes and no. I have a loaner compressor, so I have music but it is very noisy and does not pass your stylus on a stationary record test.

I will do the compliant CW arm and spring test once the proper compressor arrives.

I have been thinking about making a longer fixed counterweight rod. The current one is around the same length as original. The issue is making it stiff enough, not easy with conventional materials.

Chris.

My trash bin....
Too many years ago to count, I went about building 5 off BD TTs in quick succession. The platter was aluminium, bearing had a tungsten carbide thrust plate with replacable steel ball on the shaft. All five were of the same design, the difference being the plinth material. I simply changed the bearing, platter, motor and arm from one to the other.
#1 Laminated MDF. Slooow and colored
#2 Laminated hardboard( like compressed MDF.) Better but still slow and colored.
#3 Concrete. Hard and bright
#4,5 Slate. Quite good, slightly bright, which was mitigated with a lamination of MDF on its base. I sold #5 to a then Linn owner.
After this I went on to build 4 off unipivot arms. Based on the geometry of the Hadcock CH228. They all had saphire bearing cups with ss pins. Brass pillars and magnesium headshells.The only change was the wand material.
#1 epoxy resin infused balsa wood. This was not as stiff as expected and this was reflected in its sound, smeered and soft.
#2 hard wood dowel. Lovely, glorous, romantic but colored.
#3 undamped aluminium tube. Nice and clear with a slight rising top end.
#4 damped thin wall glass tube. Easily the best. Clear and articulate. This was broken awhile later during transportation and I was too devistated to rebuild it.

Does any one else have similar war stories? I am interested in your findings.

Chris.
Yes the glass arm was special. I used magnesium from a broken aeroplane wheel hub to mill the headshell. Slotted mounting holes to facilitate correct cartridge alignment.

I have one of the slate TT's somewhere in storage in the attic. Will see if I can find it amongst the detritus of time, maybe post some pics.

Dgarretson.

I look forward to your tests on stiffer carts.

Also re pivoted arms, I argued inelegantly a way back that the offset angle on a pivoted arm has a multiplying effect on the effective mass as seen by the cartridge. That is, the cartridge is not expending all its effort in trying to rotate are arm but a vector of this force due to the offset angle. Then of course we have to take into account the asymmetrical nature of anti skate. This could be what Mark or Poul are referring to?
With these parameters at least, chalk up a big advantage to a linear arm.

Manitunc.

Hi, if you are interested in on selling the arm without the jig, I would be interested.

please let me know.

thanks

Richard.

Second thoughts....nope. I only want the mag wand and the sleeve/spindle. All other parts would be discarded.

Manitunc.

Thanks for that. I thought that you would want to keep it, but it was worth a shot.

Cheers.

Manitunc.
Sounds like you are going to build a shop air supply. Cool.
Don't forget to earth the air lines close to the arm. Don't know if you would need 3 earth lines or just 1. Suspect 1 would be best.
What pressure do the Wisas run into the arms?

thanks

HF Dover.
Compressor is a piston type, which one would think would produce a pulsating air flow. Certainly the piston type loaner they gave me failed the Chris T noise test. The difference this time around is as follows. I'm using two regulators in series. I have a small restrictor between them, ( a trick we sometimes use for low pressure pilot hydraulics). The tank is a little larger. Its set/ reset pressures are much higher 120/80 psi v/s 60/40 psi.
I said earlier that it turned back on too frequently at around every 7 mins. When it does turn on, it only runs for approx 10 seconds. Obviously a larger tank will not only increase the rest time but also increase this on time. I could lower the reset pressure, giving a longer rest time, but there would be a corresponding increase in run time so don't plan to do this since the compressor is acoustically noisy. This can't be heard in the listening room but can in other parts of the house. Also I suspect that the regulators are more stable with a high delta P, contributing to the smooth air flow. This is certainly the case with hydraulic regulators.

Frogman.
"gas powered compressor with large storage tank"
This is kinda what I'm using now. It is a small shop air compressor. oil less type. It pumps the tank up to 120psi and switches off. Switching on again at 80 psi. The output is fed thru two regulators in series, bringing the pressure down to 18 psi for the arm.

Doing the Chris T stylus on a stationary record test, results in zero noise change out of the speakers at full volume.

The compressor turns on too frequently at present, about every 7 mins, so I will be adding an auxiliary tank to increase the time span but this is not a priority since... I hear a slight, I think, maybe, possibly, increase in noise while the compressor is running but if it is there at all, it is minute.

Chris.

Hmmm. Haven't put any thought into the trough location for literally years.
I put my design trough at the wand end to reduce any shake rattle and roll of the wand itself and by extension the cartridge. Since the key to performance of the trough is to better keep the cartridge body still, it seems to be the place to position it. We have the minimum number of joints between the paddle and the cartridge, so this should be the most efficacious place, aside from putting the paddle on the headshell like Townsend did. I was just not prepared to deal with the hassle of this approach.
My arm would need a bit of engineering to position the trough at the CW end. Difficult but not impossible.

H F Dover.
Still....relative to the groove.

Everyone else understood what I meant.

Dlcockrum

Precisely

Ketchup.

I too use your method.
If you backlight the spindle, it is possible to get a very accurate indication of when the platter and spindle are parallel. This, since you can adjust the arm such that the light evenly breaks through the gap.

Cheers.

My ET spring a leak, actually one of the o'rings failed. This necessitated disassembly. I took the opportunity to give it a spring clean and weigh it. Total weight excluding cartridge was 86 grams (95 grams with cartridge). I have on loan a standard I beam, counter weight assembly (thank you Grant) this weighs in at 47 grams, excluding the spindle clamp. This would put the total weight of a standard ET2 up to 77 grams with an aluminium wand and 85 grams with a magnesium wand. It is my intention to revisit the use of a sprung counterweight. I first did this test some 16 years ago and preferred a fixed counter weight. Before I made the decision to change, I considered the ramifications of such a move. One parameter which was looked at was tracking of eccentric records. I did not want to damage my cartridge and records with the stylus slewing about in the groove.

With this issue, resonance theory saved the day.

A way back in this thread, I posted a transmissibility graph. I had hoped that this would resolve the discussion. This shows structural movement for various excitation frequencies above and below a given resonance frequency. The resonance frequency of the counterweight assembly ranges from 2 to 5 hz. The excitation frequency from an eccentric record at 33 rpm is 0.55 hz.
If we apply this 0.55 hz input to the sprung counterweight arm, we can see what happens... transmissibility approaches 1. This means that the whole structure moves. The cartridge "sees" the counterweight.
Lets put this clearly. When tracking an eccentric record with a standard ET2, the stylus/cantilever is required to accelerate sideways, 1320 times per LP side, the TOTAL weight of the arm; wand, gooseneck, spindle, cartridge, PLUS I beam and counterweights. Depending upon the counterweights used and the weight of the cartridge, this total can approach 100 grams. The same ball park as my arm.

Harold
My music awakening happened when our school music teacher played us side one of Aqualung. She refused to play side two because it criticized the Church of England and had a bad word "balls"
I remember being stunned upon first hearing this record.

I persuaded her to let me record the album, so I took my Sony radio cassette player and placed it in front of the single mono speaker of the school record player.

Typing this takes me right back in time to the feeling of excitement and thrill of hearing this music and being able to play it whenever I wanted.

The emotional power of music.