DIY linear tonearm

[B]off topic[/B]

Niffy, since you made me want to put again the hands on a TT, here an idea for your 3 belts...

c
 

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Hi Carlo,

I think the tensioner belt is not desirable as it will allow the idlers to move which in turn will allow the sub-platter to move which will result in a worse runout of the platter. I did have the idea of mounting the motor directly under the center of the platter. I would have three idlers equidistant from the center of the motor/platter with a belt from the motor to each idler then a belt from each around the sub-platter. This would keep the tension on all belts more even and offer greater isolation from motor noise. It would also unload the motor bearing in the same way it unload the main platter bearing. Unfortunately this idea is not retrofitable to my deck so will remain a thought experiment. One motor, six belts. All the advantage of multi-motor without the downsides. Probably.

To set the tension of my belts I measured the stretchyness of the belt material then made the belts to the length required to give the desired tension.

Niffy
 
Carlo, today we've finished listening session of several hours, including progressive rock, soft rock, jazz, vocal, folk and symphonic orchestral music. We also compared Lil Casey with Shroeder clone and Micro Seiki MA-505 tonearms, all cartridges were MC. Tube phono stage, tube single ended power amp, and huge Tannoy speakers. Difference in sound definitely in favour of Lil Casey, and it is very substancial difference. It is better in every kind of music, no exceptions. For me it is first impression, however the system owner is using Lil Casey for a week, and in his opinion it is still the best sounding arm ever... Despite he is a very experienced audiophile for a couple of decades, with lots of components heard and compared.
So, congratulations again. As I predicted, the arm prefers lower compliance MC cartridges, and it will open up the best of them. Sound is as close to live performance, as any audiophile may expect.
Walter
P.S. And there Lil Casey name comes from?
 
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Glad to hear this news Walter, now i hope you'll design and build your (a springed version?); since you've already made a linear one you'll tell us the differences. Among other things, the carbon version can be made practically without a lathe (used only for the lifter, but the scrap bin may easily give the right pieces).
Sound: I listen mainly to chamber music (the only one I can follow) and melodrama (not opera), classical acoustic instruments and human voice: and we all know well how they have to sound.
So my point of view is simple: cartridge and speaker are the only things with an inevitable personality (choice is a matter of taste). All the rest should do only one job: disappear.
So what does "better" mean? It sounds clean and convincing (this also applies to the Rabbit PLT), but different from a serious (simple and rigid) pivoted one. And I wonder how this comes from - suspicion on how the side force is generated

carlo
The name comes from - Jr Casey - the small, snorting Disney locomotive YouTube
His gait, the efforts in moving the elephants load reminded me of some linear ones seen before, diy & commercial.
 
As to the sound. More space, higher resolution, more detailes, more openness. Very good and articulated bass. At the same time, there is nothing too much, so no irritation or tiredness.

I've never pursued higher resolution and more detailed sound, as it often irritates and even divides musical content. In this case, for the first time extremely high resolution just brings more narural sound and more music. A big surprise again. I would even take a risk to say there is nothing I would like to improve sonically.
As to my own design, it is very different. It is a pivot arm, but at the same time, it is true linear one. Of course, I will finish it, but for now I don't think it will sound as good as yours.
 
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(....) It is a pivot arm, but at the same time, it is true linear one. (....)

Highly interesting, Walter, especially if you're going the passive way; keep us informed.
I am more and more convinced that if we want the stylus to be centered into the groove, the arm movement must be get from the stylus drag, not pushing on one side.
Don't know how, just some hypotheses.
carlo
 
Hi Walter,

Often components that appear to be highly detailed and resolving have a peek in the output at around 8khz. This leads to a false sense of detail but will ultimately lead to a harsh fatiguing sound. With a tonearm this is normally due to the arm having a bending mode around 8khz, this is often a headshell resonance. With long conventional arms compression waves that travel down the arm bounce off the counterweight and return to the cartridge. If the time it takes the wave to make the round trip roughly equals the period of 8khz this can also add to the false sense of detail.
The lil casey has totally eliminated the armtube and minimised the headshell so the bending modes that plague conventional arms do not arise. Also the compression waves don't have a large counterweight to bounce off and the time it takes a compression wave to make the round trip in the tiny carriage will equal a frequency that's probably well above 20khz.
My guess is that the detail you are hearing is "real" detail which is why it is not fatiguing.
Minimising tracking errors compared to standard pivoted arms has got to help to.

Hats off to Carlo for inventing the first new working concept in tonearm design that's been seen in years. Note I said working concept as there have been a lot of concepts that don't work.

Niffy
 
quote Niffy: in fact I am also the inventor of the Syrinx, the silliest of the failed TA. And, even worse, still convinced that the Thales is the right geometry to follow.
So let's stay calm, Lil Casey has only bypassed one problem, and needs a lot of improvements: a kind of work that bores me right away.
As someone said: "That’s one small step for mankind, but one giant leap for a man"
or was it different? such a long time...

carlo
 
arm

Niffy, Carlo. I would argue as to bypassing only one problem by Lil Casey. It seems to be a simple and compact design, pretty user friendly. Sound is wonderful.

As to my own design, it is passive arm, with no counterweight. However it has kind of short armtube. I'm curious, if it will have usual compression wave influence. Precise machining is the main obstacle to complete it soon.
Walter
 
Hi Walter,

With a compression wave the amount of reflection at an interface between two materials is determined by the difference in mechanical impedance of the materials. A low impedance interface, where the materials have a similar impedance, will result in a weak reflection. A high impedance interface, where the materials have a big difference in their impedances, will result in a strong reflection. Also a small object will reflect less than a large object of the same material. The counterweight of a typical tonearm normally has a high impedance interface with the armtube. Combine this with the need to make the counterweight heavy and large results in a strong compression wave reflection from the counterweight. By removing the counterweight and replacing it with a spring you remove a high impedance interface and therefore the reflections that would have occurred at that interface.
I used the example of the counterweight as it is one of the major sources of reflection in most arms. However it is not the only source of reflection. The interface between the arm and the air that surrounds it is quite high impedance so there will be a strong reflection from the rear of the arm regardless. Also not all counterweights have a high impedance interface with the armtube so do not create a reflection such as the Helius Omega that has the counterweight no only made of the same material as the armtube but is part of the armtube. As short effective length linear tracking arms only need small counterweights they tend to have much weaker reflections than from a large conventional counterweight.
Other areas in the arm that may have a high impedance interface are at the bearing yoke and the connection of the headshell to armtube, especially if of the removable variety.

Niffy
 
Hi Walter,

By making the headshell from the same material as the armtube reflections at the interface can be minimised. You will still have a small reflection but not to the extent that you would from dissimilar materials. Ultrasound is commonly used for nondestructive testing to look for cracks within a material, the sound being partially reflected at the crack even though all the material is the same. Most detachable headshells have several different materials in the join which can cause multiple reflections. One caveat is that the time it takes for the sound to be reflected back to the cartridge from the join will be very short as the distance is small. Reflections are most problematic if they match up to either whole or half wavelength as this causes constructive or destructive interference. The short distance to the joint will tend to have a reflected length less than a quarter wavelength at most audio frequencies which will reduce the audibly of the reflections. This is another advantage of using a short armtube in a linear tracking tonearm.
The biggest disadvantage of using a detachable headshell is loss of rigidity at the join. In my carriage I chose to forgo having a headshell in the traditional sense. I also have no armtube. The cartridge sits within a recess within the front of the carriage that encloses it from 4 sides. The sides of the recess form buttresses that extend to the front of the cartridge. This arrangement would be very difficult to duplicate with a detachable headshell without either increasing mass or reducing rigidity. The counterweight sits in a similar recess in the rear of the carriage.
The obvious advantages of making the headshell detachable is the ability to easily swap cartridges and the facility to adjust azimuth. For me easy cartridge swapping is a non-issue as I only use one cartridge and like an arm that I set up once and forget. I think that in most cases the addition of azimuth adjustment costs more than it benefits. I took great care to make sure that the mounting surface was exactly parallel to the plane of the bearings. Fine tuning of azimuth by rotation of the headshell is actually next to impossible regardless of the claims of reviewers and manufacturers. To adjust azimuth by 1/10th of a degree would require that the cartridge mounting screws have to move by about 1.1um (assuming the axis of adjustment is on the same plane as the screws) . Even the smallest manual adjustment is likely to move the alignment by several degrees. You are more likely to get good azimuth alignment with an accurately made fixed headshell.

As you can probably guess, I'm not a fan of the removable headshell.

Niffy
 
Detachable head shell?

Aside increased effective mass, and 8 useless contacts almost no difference, just remember to braze it to the wand after installing ...
I'm joking, but I think it suffers from a weak design* that can resonate like a reed musical instrument. A simple conical or flange joint would suffice to avoid it, as even the worst mechanic knows. (attachment A)

The Azimuth adjustment - imho - has greater consequences than the VTA, as well as skating or carriage friction compared to the (small) tracking error (attachment B - see also attachment on #2556)
Adjusting the azimuth can be very simple, just laying the head shell on a square block on the surface of the platter; hoping that the cartridge manufacturer works with strict tolerances (it's needed machinery and procedures that are anything but artisanal).

carlo
* Shortly after inventing the detachable headshell arm (a very welcome pastime) it's designers came out with the "Series II - improved", without it.
 

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Niffy, Carlo. I assume that from the point of physics , Lil Casey rail tube may be considered, as kind of armtube, and carriage as kind of headshell. However, IMHO vibration energy transmission between them is strictly limited by decoupling with small balls. So, said reflexion waves influence minimized. Maybe, this is why the arm sounds so good? I don't think such a huge sonic difference is due to linear movement and abscense of both skating force and angular mistake...
As to removable headshell, I'm in need of it, because I do cartridge repairs, and must often change carts to hear results. By the way, I do have possibility to compare lots of rare and legendary carts (and who can resist against such possibility?). Changing them on a solid arm is real pain in the ***.
Sure, two arms, or even two turntables is the way out, but I hope to create removable headshell , that is sound friendly and transparent. At least, I will try.
Walter
 
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Walter, you're right, the resonances travel across the Lil Casey more or less like in any arm, but the carriage balls don't give any decoupling (or chattering) because they are forced by their number, and the self centering to be always in touch.
In the first Lil Casey the decoupling occurred at the level of the 8 parallelogram bearings (the "needle talk" was audible up to that point) in the second one the elastically mounted pen tips are always in contact, and the needle talk is minimized everywhere (even the material matters, the carbon fiber is as rigid as ergal, with similar SI but "sounds" differently, on lower octaves).
Maybe the difference you feel should be sought elsewhere: the pivoted TA suffer from tracking error and skating force, while the linear ones from side force (similar forces but on different channels); the radial rail was born to limit the SF abolishing the negative arm lever. Even a consistent VTA (the vertical movement is also parallel) may have a small influence.
So probably it should sound like a short arm air bearing linear: but I only know a Ladegaard bad diy clone that suffered from an enormous lateral mass, and obvious vibrations caused by the air flow = pure garbage

Head shell: to change the azimuth - not the head shell - since many years I'm using the flange solution, which gives no decoupling (thinking as Niffy, absolutely rigid chain + mechanical grounding). It should not be impossible to make a series of interchangeable head shells better than the standard ones: for example the screw could be replaced by an eccentric, or making a conical joint with a snap locking etc

carlo
cartridge repairs? all my compliments, Walter. I tried once simply to straighten a bent cantilever, and destroyed a cartridge
 
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Carlo, maybe I've used wrong word. By decoupling I mean not chattering, but limited energy transfer caused by point contact (on our case two point contacts). The same way spikes do in hi-fi equipment,( including speakers, decoupled from the floor by spikes). I suppose, in Lil Casey case it is an important factor.

As to the cartridges, I've even completed few of my own design, and the mono version is really good one, the stereo versions having no advantages over the existing brand ones (yet)...
 
Useful comparison, but it is not a de-coupling, imho: concentrating the weight force in one point the spikes anchor the speakers to the floor like bolts*, grounding the enclosure vibrations in a much greater mass. (= sound change)
By designing the radial rail I was worried about the lightness needed for the carriage+head shell. This remembering when I was convinced of the need for damping and insulation (it's the simplest story to tell to customers, says an old friend seller). De-coupling carefully the cartridge from the arm led to the strangest behavior: colored sound, resonances bursting suddenly on certain frequency ranges. It took me a while to realize that waves were bouncing closed inside the cartridge body, in a way completely not previewed by manufacturer. Instead we need to remove them, disperse, and limit the feed back.
Even if the spheres are not spikes seem to work fine: I think (well, I hope) that the point contact stiffness makes the cartridge see a mass up to the whole arm + plinth, not only his lightweight carriage.

carlo
* the funniest is that someone sells together some washers not to damage the floor, making the spikes completely useless!
 
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P.S. And there Lil Casey name comes from?

Hello walterwalter and Carlo,

The origin of the name Casey actually goes back further than the cartoon by Walt Disney. Walt Disney himself got the name from American Folk Hero Casey Jones, an engineer, who died in a train collision in 1900.

Casey Junior | Disney Wiki | FANDOM powered by Wikia

Casey Junior is a young, anthropomorphic steam locomotive fromDisney's 1941 animated feature film, Dumbo. His name is a direct reference to Casey Jones, the famous railroad engineer who had lost his life in a train collision in 1900.

Sincerely,

Ralf