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Old 15th February 2019, 06:03 PM   #2751
Coolerooney is offline Coolerooney
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Hi all
Found this

Defects in Gramophone Records

It makes you wonder.....
Best,
Coolerooney
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Old 16th February 2019, 03:54 PM   #2752
niffy is offline niffy  England
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Quote:
Originally Posted by walterwalter View Post
Niffy, I do have a question, as to bearing noises. For motor, platter bearing, as well as idler drive, I can clearly hear the noise, both directly with stethoscope and through the speakers. As to tonearm bearing, I'm unable to hear any kind of chatter, as well, as other noises (other than those, coming from the motor and drive)... What is your opinion of how chatter influence on sound happens, and how to detect it?
Picture shoves, how I tried to detect the arm bearing noise. Cartridge, placed directly on the arm with stylus in contact with the arm body near the horizontal bearings. Cables go into the phonostage.
Sorry, the arm is not linear.
Walter
Hi Walter,

Good question. Rumble and motor noise are generated independently from the record and arm and are relatively easy to measure in isolation.
The main source of energy that drives bearing chatter is the modulation of the groove itself. When playing a record the cartridge body/arm do not remain absolutely stationery but move out of phase with the groove modulation. The amount the cartridge moves is very small at high frequencies but can be surprisingly large at low frequencies. At 20hz the cartridge can be moving over 30% of the amount the stylus is moving. A 60um peek to peek modulation can cause the cartridge to be moving by more than 20um. At 50hz the cartridge moves about 4% as much as the stylus. By the time you get to 100hz it's only 1%. Even if your system can't play 20hz the arm can still be moving a large amount at this frequency.
Chatter is caused by this shaking of the arm making loose components in the bearing rattle.
Not all types of bearing suffer chatter, only those that have loose components. Ball race bearings are particularly prone to chatter as only the balls that are under load are restrained. It is possible to restrain all the balls in a ball race by applying a load parallel to the axis, pre-loading. This will increase the friction of the bearing. Applying grease or oil will damp the motion of the loose ball and will reduce or even eliminate chatter. Unfortunately this also increases friction. When using ball race bearings in a linear arm the bearings cannot be pre-loaded and have to be run dry. You can get away with pre-loading and lubricating the bearings in a pivoted arm as the bearing only rotates through a small angle and the armtube acts as a lever reducing the effect of bearing friction. The smaller angle of rotation can also reduce chatter as the movement at the bearing is lower. Compression waves travelling through the arm can also excite loose balls and may even be the predominant mechanism. There will be certain frequencies that cause chatter more than others, like the annoying rattle in your car that only occurs at certain speeds.

As chatter is at a much lower level than the groove modulation it is very difficult to isolate it. It is also difficult to alter the chatter to the bearing without also altering its level of friction or grounding. It is therefore difficult to determine whether a change in sound is due to reduced chatter or reduced friction or improved grounding. When developing my bearings I made 6 different rails and more than a dozen different wheels and bearings, including ball race. I tried to change as little as possible between each iteration so I could pin down what caused what change. I even made a rail that was designed to fail just so I could see if it failed in the way I expected. From this I determined that chatter plays a significant role in the sound quality of a mechanical linear tracking tonearm that utilises ball race bearings.

In extreme cases bearing chatter will add a harsh gratings edge to the sound. More commonly the effect is a more subtle veiling of detail and microdynamics.

I don't think your test set up is likely to reveal much. A phono cartridge works due to the relative motion between the stylus and cartridge body. In your set up both the stylus and cartridge are held stationery relative to the armtube. If it did reveal anything it would be how much the cartridge/arm is moving relative to the groove. If you could place the stylus directly against the bearing you might pick up something.

As long as it's DIY it doesn't matter if it's linear.

Niffy
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Old 16th February 2019, 05:10 PM   #2753
carlthess40 is offline carlthess40  United States
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Has anyone ever tried to isolate the cartridge and needle from the tonearm with either a dampening material or a isolator method like you would for Speakers to the floor or the amps the a shelf?
Just spit balling here
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Old 16th February 2019, 06:41 PM   #2754
walterwalter is offline walterwalter  Ukraine
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Niffy, thank you for detailed reply. As to my experiment with the cartridge, as tonearm parasitic sound sensor, it is rather encouraging. My first attempt was with a small microphone, and it happened not having enough sensitivity to detect any arm vibrations at all. Phono cartridge is a much better sensor, if placed properly. In my case, it has only two points of support: A made of four flexible wires, and B the stylus, cartridge acts as kind of effective mass, together with wires it makes tonearm-like arrangement, so the stylus able to detect tonearm body vibrations, further amplified by phonostage. Actually, I tried to hear, how the arm body resonates and sounds to make up my own opinion. In my case, wooden arm body has it's own sound, but it is of so miniscule level, that should be completely disregarded.
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Old 16th February 2019, 06:50 PM   #2755
niffy is offline niffy  England
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Hi Walter,

That makes more sense.

Niffy
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Old 19th February 2019, 03:30 PM   #2756
niffy is offline niffy  England
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Default Don't you just love it when an experiment fails

Hi all,

Still slightly off topic. I've fitted the new idler wheels and bearings. I wanted to make 4 changes over the previous setup even though they were almost perfect. The old ones had a very slight wobble (I'm only talking 10s of microns). Using techniques developed building the arm bearings they are now pretty much perfect . I wanted the ability to run higher belt tension so I could experiment to find the best possible. The new bearings are definitely able to take several times as much tension as the old. I also want to be able to use different or even multiple belts run in a rather unconventional manner. The new setup will allow this and will hopefully help to reduce platter runout. The old bearings were very quite. I could just hear them with a stethoscope pressed against the upper bearing mount, I could hear nothing from the lower mount. Unfortunately the new bearings are quite a bit noisier. If I strain my ears I can just hear the lower bearing. The upper bearing is quite noticeable. Now I have the joy of investigating tribology further and building more bearings until I get a perfectly quiet design. The increased bearing noise has only mildly effected sound quality, a slight veiling of micro dynamics, similar in nature to low level bearing chatter. It's one of those differences that's so slight it's difficult to pin down. I was surprised by how little difference the bearing noise made, the work put into resonance control in the subchassis seems to have paid off. After I've sorted the bearings I have the fun of investigating belts.

So I wouldn't call it a complete failure as 3 of the 4 improvements paid off. I think I'm on the right track.

Niffy
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Old 19th February 2019, 04:09 PM   #2757
hottattoo is offline hottattoo  United States
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Niffy,

If possible and get some time, could you post some pictures of the bearings you are trying to improve ? I have a hard time picturing your turntable drive system. good luck with your research.
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Old 20th February 2019, 06:44 AM   #2758
nocdplz is offline nocdplz
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radial rail tonearm - carbon

I am slowly redesigning, simplifying the first Lil Casey, looking for a compact and easier to build solution. I have kept what showed to work well (non recirculating balls carriage - rotatable leveling base - lifter - CW regulation) trying to improve the rest (weight of vertical masses - vertical articulation - bearings). That's why a 12 mm carbonfibre tube, that should reduce the vertical mass to 25 gr ca: an acceptable value, similar to the horizontal one (< 20gr).
In addition to weight, the major revision relates to the parallelogram: the slanted version, that gave no real advantage, is substituted by a straight one with the rail between the levers to get the same couple on upper - lower bearings.
Bearings become pen-tips type, hoping to reduce the friction significantly. Unfortunately still couldn't get 4 pairs of jewel bearings without opening first a watch factory.
As usual my design refers to my tools, my skills, and materials I can find. I'm not saying it's a tonearm for newbies but needs only patience, accuracy. and simple tools (no lathe)
Sorry, no fancy tech.

carlo
Any advice?
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Old 20th February 2019, 12:12 PM   #2759
niffy is offline niffy  England
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Hi Carlo,

You sometimes find used jeweled bearing parts on ebay.
100x holed watch jewels new old stock repair ruby hole watchmakers jewel parts | eBay
100x Top cap jewels for watch new old stock repair watchmakers parts watches | eBay

These are the ring and end cap type bearing in assorted sizes. Might be a help.

Niffy
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Old 20th February 2019, 02:49 PM   #2760
nocdplz is offline nocdplz
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Thanks for links, Niffy. Finally something useful, even if I'd like to find the springed version V bearings with their pivots. Banggood, Aliexpress and some sites of Swiss and American producers seem all B2B oriented.
Now a friend told me about a repairer of industrial clocks here in the area, so I'll try first to hear him.

Hoping to avoid tilts, I've made some tests of carriages on a square section, but without satisfactory results without greatly increasing the base, and therefore the overall weight. Add to this that square tubes in carbon > 8x8 are almost unavaible, and I'm back to the round solution, already tested.
Hope the carbon tube could be sufficiently straight, hard and smooth for the task. Unlike you I have no experience with carbon (just used for the arm wand)

carlo

I read about your computer. Horrible. Have you heard those who recover data from broken hard drives? sometimes miracles do happen
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