Thanks, indeed many things amuse me. The 12kHz AM modulation is puzzling, because AM requires a multiplication stage but there isn't an obvious source of that. Perhaps what might be displayed is FM modulation (caused by eccentricity varying speed), then 12kHz aliasing with the display resolution ? But I can't see a connection between eccentricity and friction variation, because variation in both forces and alignment angles involved in moving the tonearm to accommodate are so small.........
Likewise, personally I've not observed a general relationship between crackle-pop noise and eccentricity or warp, unless really pronounced - then I've thought it sounds like wear burn, perhaps due to stiff tonearm bearings on previous equipment ? However, some pressings have once per revolution crackle-pop, which I attribute to variation in vinyl compound around the pressing, affecting friction surface. I don't think it necessarily correlates with eccentric centering though.
It's there when you zoom in, since it's 1/3 octave noise centered at 12kHz I assume it's due to all the intermods in some way. BTW I modified an external sound card to do DC, it's surprising how much .55Hz and its harmonics are at the input.
Here's a few measurements which nicely show some benefits of reducing friction. They date from my experiments with water as a lubricant, which sparked my interest in the whole opportunity that reduced friction can offer to vinyl playback. It can be profound, IME.
First is a plot of IMD spectrum, for dry and wet playback of the same test record. It not only demonstrates no change to IMD performance, if anything a small improvement for wet playback, but very nicely demonstrates profound improvement to noise floor.
Second plot is measurement of low frequency spectrum whilst playing a pink noise track. Shows profound reduction in low frequency headshell wobble with wet playback, repeated 3 times because I did not initially believe the result ! It took a long time before I could work out why this might be so. Skate force depends on friction force, and random noise variation in it is a stimulus for headshell wobble. What the graph shows is a reduction in low frequency stimulus associated with reduced random variation in friction.
Interesting ?
PS: I'm not advocating wet playback. Just a means to an end in terms of demonstrating effects of reduced friction.
First is a plot of IMD spectrum, for dry and wet playback of the same test record. It not only demonstrates no change to IMD performance, if anything a small improvement for wet playback, but very nicely demonstrates profound improvement to noise floor.
Second plot is measurement of low frequency spectrum whilst playing a pink noise track. Shows profound reduction in low frequency headshell wobble with wet playback, repeated 3 times because I did not initially believe the result ! It took a long time before I could work out why this might be so. Skate force depends on friction force, and random noise variation in it is a stimulus for headshell wobble. What the graph shows is a reduction in low frequency stimulus associated with reduced random variation in friction.
Interesting ?
PS: I'm not advocating wet playback. Just a means to an end in terms of demonstrating effects of reduced friction.
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Lots of folks do a clean and play wet, I've even seen "pouring it on". BTW why does the noise floor wet/dry at 1k look the essentially the same in the second plot?
Yes, no doubt eccentricity has profound effect of its own, just I don't see the connection with friction.............
BTW, here's a neat way of looking at profound FM effects of eccentricity, the mechanical source of 0.55Hz IMD. For a test tone c 3kHz, once round the plot is one platter revolution, radius is 'instantaneous' frequency. One can also see warp and headshell wobble, as well as motor speed variations on these plots.
This plot happens to be a SP10 versus a 1200, red and blue traces.
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Because it's not the noise floor, it's playing back a pink noise test record so at 1kHz that is programme material. Another test record bought that bit the dust.......
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After playing wet, some (but not all) records measure significant increase in coefficient of friction in subsequent dry playback IME from my own tests. Many end up with higher coefficient than before wet playback. Those records which show this increase also show increased crackle-pop noise, and those which don't, don't. So I suppose wet playback can somehow permanently alters the vinyl friction surface, but don't know enough about vinyl polymer mechanics or tribology to explain why.
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Lencoclean
I have heard that wet playing permanently damages (some?) discs.
If that is the case, why wouldn't vacuum cleaning like VPI or Monks do the same thing? Or ultrasonic cleaning?
When I used the VPI 16.5, I got the disc wet with the patented cleaning solution, bore down on it with the special brush, then vacuumed the water off.
I ask this in the spirit of speculation, because I never did controlled experiments with the VPI. I simply assumed that it would clean the record more thoroughly than my previous efforts with the Discwasher.
I guess the experiment would involve getting three identical pressings, playing them pre-cleaning to observe their "as-pressed" spectra, then subject them to the various cleaning methods and review their post-cleaning spectra.
I have heard that wet playing permanently damages (some?) discs.
If that is the case, why wouldn't vacuum cleaning like VPI or Monks do the same thing? Or ultrasonic cleaning?
When I used the VPI 16.5, I got the disc wet with the patented cleaning solution, bore down on it with the special brush, then vacuumed the water off.
I ask this in the spirit of speculation, because I never did controlled experiments with the VPI. I simply assumed that it would clean the record more thoroughly than my previous efforts with the Discwasher.
I guess the experiment would involve getting three identical pressings, playing them pre-cleaning to observe their "as-pressed" spectra, then subject them to the various cleaning methods and review their post-cleaning spectra.
I don't see any evidence that wet-playback has the stylus banging around, quite the opposite. All pointers are that stylus follows the locus of the groove base better (if anything) than for dry playback, ie 'bangs about' less. Otherwise it would show up in noise, THD, IMD, f resp measurements somewhere, but doesn't.
I suppose it has something to do with changes to the vinyl surface under pressure in the presence of water, but I really don't know, but I know of no evidence of mechanical misbehaviour, quite the opposite..........
For the TD160 platter the rotational kinetic energy is ~250mJ at 33.3rpm
(hoping your family is doing well)
Cavitation maybe an issue.
Hydrodynamics is a complex field. The more the liquid film is squeezed and the more abrupt it’s thickness changes, the chances for cavitation formation increase.
My opinion is that the damaging of the groove walls from cavitation can be seen through an optical microscope.
George
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Yes I found the same problem. So I made measurements of friction coefficient versus: f response, noise floor, THD, and IMD, and that is what I based my opinions on. These results aren't published and aren't reviewed, but I believe them to be robust, repeatable and certainly sufficient for the purposes I have, and on a balance of probabilities seem safe to use as indicators.
It would not surprise me if changes to vinyl surface were visible with good microscopy. But the leap to cavitation as an explanation, though plausible IMO, is not confirmed AFAIK. The fluid layer is under great pressure for a very short time, and I'd imagine examination of available energy would be revealing as to whether the dynamics supports cavitation - I don't know enough to comment. Where is a tribologist when you need one ?
Some records survive wet playback without audible degradation in dry playback noise floor IME, but it's a minority, and that has to be explained either way.
And yes, with such a range of platter inertia available, stored rotational energy can vary by more than an order of magnitude and ~250mJ is also plausible. For the stopping method as per Pardee's paper, what matters really is that stopping time from bearing friction alone is as long as can be, and >90s is a good target for accurate measurement of stylus-groove friction measurement IME, which implies a high inertia platter.
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