AR XA tonearm reveals its secrets

american simplicity
gkimeng
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Re: AR XA tonearm reveals its secrets

Post by gkimeng » 31 Aug 2019 19:29

The Best headshell is injection molded, while the Pat's appears to be a 3D print. I'd opt for the Best simply because it looks more original and doesn't have that grainy texture that is a characteristic of the 3D printing process.

oztayls
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Re: AR XA tonearm reveals its secrets

Post by oztayls » 03 Sep 2019 02:41

oztayls wrote:
22 Aug 2019 01:04
My XB1 arrived yesterday. I've been looking for a nice one to replace the one I stupidly sold a few years ago. This one is in pretty good original condition, unmolested and has its original box and packaging. The bottom was still held in place with staples and the owner said it hadn't been used for 40 years. The only downside is the Fidelity Research FR-6SE cartridge has a broken cantilever. :( (I’ve only serviced it, but have yet to spruce up its looks.

Anyway, I digress because I'm pretty excited about what transpired yesterday after I had serviced it and removed the old oil and grease. As you know I've been fiddling with anti-skate on my 2 XAs using two methods, i.e. the draped weight method as per the pics I posted earlier, and the viscous drag method using silicone oil blends. After cleaning out the arm well of the XB1 and finishing the clean out with an IsoPro cotton tipped applicator, it was totally free of oil, so I thought I'd give my new idea a try. I don't know why I had dismissed the idea of using 500K CST (500,000 CST), but maybe it was because I thought it would be way too thick and the viscosity much too high. (I have been fiddling with blends using 500 CST and 300K CST and this was only somewhat successful) I decided to wipe some neat 500K CST onto the arm tube and bearing. This is the same stuff I always use to restore arm set-down mechanisms. The result was that I could really notice the slight drag on the arm as I move it back and forth.

IMG_4762.JPG

Playing the first record was a revelation. Not only are the channels perfectly balanced, but suddenly, I could notice a significant improvement in bass and treble extension. There was more drive and punch too. Then I got to thinking about what was going on here. The swinging arm in the tube is basically a viscous clutch and works in the same way as the cylinder in the XA's arm. When the cylinder moves relative to the arm post, initially there is drag created when the bonds of the oil molecules are stretched, but then they "catch up" whereupon the status quo is re-established, and arm stability is restored. Because the arm is moving very slowly, one groove at a time, the drag on the arm is actually very small and the oil molecules are only being stretched minutely. Placing the stylus on a video disc reveals how well the anti-skate is actually working. Instead of the arm racing across the disc to the centre, the arm traverses slowly. According to Peter Ledermann of The Soundsmith in his discussions on anti-skate, this is pretty much ideal. Of course, it’s not absolutely perfect as centripetal force gets stronger the closer to the centre that the stylus gets, but it’s a good average.

The other happening thing is the improvement in sonics that I seem to be hearing with the viscous anti-skate, but then I recall what Ed Villchur and others have mentioned in their arm discussions and perhaps it’s not to be unexpected. EV said that he chose a plastic for the headshell to reduce the mass at the end of the arm and that he could not achieve the same low mass with aluminium. The purpose was to help overcome some of the inertia that is created at the end of the arm as it traverses the grooves, which in turn translates to improved efficiency for the cantilever which can pass through improved vibrations, and ultimately, improved sound benefits. He said that if you can stabilise the headshell, the cantilever will be able to transmit more of the vibrations from the record grooves to the cartridge, and sonics will be improved. What the viscous anti-skate does is further stabilise the headshell. This is also the purpose of the silicone oil moats seen on some expensive arms, so it’s an established design concept. As a by-product of the viscous anti-skate, there is improved damping of the horizontal arm motion which stabilises the headshell and in turn this must result in better transmission of cantilever vibrations into the cartridge.
To my mind, I think the viscous anti-skate is a win win for better sound from the AR. I would like other AR owners on this forum to give this a try and let me know what they think!

Note: For this to work, the arm well and arm post need to be absolutely free of oil, and dry. A fingernail amount of 500,000 CST is all that is needed. A little on the bearing and a thin, even coat on the arm post. Moving the arm from side to side to side across as wide an arc as possible, taking care not to stretch the tonearm wires, will ensure the oil’s even adhesion to the surfaces. Then stick on a record and let us all know if it works for you!
Since writing the above post, I installed the CST 500K anti-skate on one of my two XA's as well. On both turntables it's proved to be the beezkneez and a much easier way to implement anti-skate on these tables than the draped weight system. The beauty of it is that it's completely dynamic as the stylus tracks across the record surface. Queuing a record is also easier as I can let the stylus on both the XA and XB slowly descend to the record without the anti-skate taking over and moving the stylus off the record as it descends. Also, no more channel balance issues now.

derspankster
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Re: AR XA tonearm reveals its secrets

Post by derspankster » 04 Sep 2019 03:26

What is a CST 500K Anti-Skate?

oztayls
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Re: AR XA tonearm reveals its secrets

Post by oztayls » 04 Sep 2019 04:27

derspankster wrote:
04 Sep 2019 03:26
What is a CST 500K Anti-Skate?
More detail in my earlier post, but essentially it expands on Villchur’s original idea of using a silicone grease on the arm post to create “drag”. This drag counteracts the natural centripetal force pulling the arm toward the spindle.
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l

lenjack
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Re: AR XA tonearm reveals its secrets

Post by lenjack » 04 Sep 2019 15:26

I don't think he did it to create drag.

1200y3
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Re: AR XA tonearm reveals its secrets

Post by 1200y3 » 04 Sep 2019 17:20

The weight on a string has got to be the simplest and most effective antiskating that will keep perfect balance in order to create compensation. It is a simple DIY modification project as well.

Silicone grease will give the arm "damping" as opposed to drag. The arm has to have instant vertical response (up-down warp following ability without causing the needle to teeter), but it should be solid in the side way movement area. The silicone will help clear up a "loose end", as well as provide some shock absorbency. But for anti-skating it lacks enough strength for tone arm leverage, and it needs to be adjustable for VTF increases/decreases. Nonetheless, the silicone may function OK as well.

derspankster
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Re: AR XA tonearm reveals its secrets

Post by derspankster » 05 Sep 2019 00:58

I can't imagine adding silicone in the horizontal tonearm bearing doing anything positive to the performance of the arm.

1200y3
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Re: AR XA tonearm reveals its secrets

Post by 1200y3 » 05 Sep 2019 17:10

I forgot to state that most anti-skating will actually need enough force to pull the tone arm out.

oztayls
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Re: AR XA tonearm reveals its secrets

Post by oztayls » 05 Sep 2019 23:44

1200y3 wrote:
04 Sep 2019 17:20
The weight on a string has got to be the simplest and most effective anti-skating that will keep perfect balance in order to create compensation. It is a simple DIY modification project as well.
A few weeks ago I would have agreed with you. This is the pic I posted earlier in this thread of the simple mechanism I made which also works very well.
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However, I was intrigued that Villchur had seriously considered a fluid dynamic anti-skate method and now, since trying the silicon grease on the arm post, I "get" what Villchur was on about. Villchur was a smart man and he clearly knew his hydrodynamics. In fluid dynamics, drag is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. It is now clear to me that he designed the XA's arm post with the intention of using fluid dynamic drag (viscous clutch) as the anti-skate mechanism, otherwise he would have used a system with much lower friction, such as a needle bearing for his arm. In fact, the wide arm post is a similar design to the viscous clutch he uses for his "butterfingers" mechanism. For a viscous anti-skate, he would need a larger surface area for the arm post and the tube, and this is exactly what we have in the XA/XB arm!

Apart from hydrodynamic drag acting as the mechanism for the opposing anti-skating force, there is also a significant damping mechanism which is absorbing unwanted resonances. This further improves the performance of the arm. That AR did not proceed with it commercially is likely due to the difficulties of implementing it correctly once in the customer's hands, and also the likely unavailability of a commercially available suitable grease at that time.

When I decided to give CST500K a try, I wasn't confident it would work very well. It was merely a dabble after reading of Villchur's interest in this method. That it works as well as it does, was quite a surprise and I'm not cleaning it off any time soon. It works better than the draped weight system I made earlier, and this is confirmed by my ears as well as the VU meters on my Yamaha A-S1100. Why would I when the performance of the arm has improved way beyond my expectations?

1200y3
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Re: AR XA tonearm reveals its secrets

Post by 1200y3 » 06 Sep 2019 07:11

Viscous damping was actually the standard for years before the A/R. Gray Research (early 50's) and Micro-Trak broadcast arms used silicone damped pillars. But the SME 3009 was using the weight on the string design at the very same time the A/R came out, so A/R wouldn't need to sell that feature. Anti skating was a competitive idea due to Garrard's "bias" invention.

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Re: AR XA tonearm reveals its secrets

Post by fscl » 08 Sep 2019 17:48

While searching another topic came across the following link contributed by "guest" in a reply to dlaloum. From the Boston Audio Society 1975 supporting Edgar V. design / intent and your own personal experiences.

The tonearm dampening paper starts 22 pages in.

http://www.bostonaudiosociety.org/pdf/b ... -7501b.pdf

Fred

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Re: AR XA tonearm reveals its secrets

Post by lenjack » 08 Sep 2019 18:24

damping

gkimeng
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Re: AR XA tonearm reveals its secrets

Post by gkimeng » 14 Sep 2019 20:24

There is NO damping of the horizontal movement of the AR arm. The only damping in the arm is vertical, and it is engaged ONLY when the arm is being lowered onto the record or lifted off it.

Do NOT put grease on the arm post.

lenjack
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Re: AR XA tonearm reveals its secrets

Post by lenjack » 14 Sep 2019 21:00

Right. The damping that Villchur designed in, was purely to prevent the arm from falling rapidly to the record or platter if it was accidently dropped.