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Pioneer PL-990 turntable clipping, [moved from General Audio/TOS #6]
mzil
post Nov 5 2013, 17:07
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QUOTE (claudiod @ Nov 5 2013, 07:59) *
Now, I am still wondering why only the 45rpm and not the 33rpm were damaged (both were played on the same old mono turntable for 30+ years), and why only half side of the wave is damaged. Probably due to mechanical reasons such as different speed and centrifugal force?


Playing records at 45 RPM instead of the slower 33 causes more groove wall friction and heat, which over time will damage the vinyl surface, especially if the stylus has an incorrect tracking force, alignment, is chipped. worn down, caked with dirt, mono stylus use on stereo LPs, etc.. This problem is exacerbated by repeated playback and turntables that have an "auto repeat" function that are left to re-play the same side over and over again was not uncommon in many designs. As an analogy, if you rub your hands together slowly [33 RPM] there is no perceptible heat build-up, but if rub your hands together quickly [45 RPM] you can warm them up, due to the friction.

As for one channel being more damaged than the other, I suspect that's because of skating force. This lateral force applies more pressure against one side wall than the other. To the best of my knowledge your PL-990 turntable has no "anti-skating force" mechanism to neutralize this imbalanced pressure [although as I suspected the major damage was done previously during earlier plays, not your current playback, so swapping the TT with one with an anti-skating mechanism wouldn't help these records. Sorry.]

P.S. I've owned some top-flight TTs without any anti-skating mechanism, BTW. It is a relatively mild and usually inconsequential force, so the need to neutralize it is debatable, but when there is an issue, such as the problems I mentioned above (e.g. an incorrect, downward tracking force), it explains why the deformation is skewed toward one channel (one groove wall) more heavily than the other. Its primary importance is to ensure that when the needle is lifted from the grooves (either intentionally by the manual cuing control, or accidentally due to a very large warp in the record which launches the cartridge off the surface), that it returns down to the same groove, instead of skipping a groove or two.

This post has been edited by mzil: Nov 5 2013, 17:12
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cliveb
post Nov 5 2013, 19:28
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QUOTE (mzil @ Nov 5 2013, 16:07) *
P.S. I've owned some top-flight TTs without any anti-skating mechanism, BTW. It is a relatively mild and usually inconsequential force, so the need to neutralize it is debatable

I'd venture to suggest that a "top flight turntable without anti-skating" is an oxymoron (unless it has a linear tracking pickup arm). What make/model are you referring to?

Let there be no doubt about this: a turntable with a pivoted pickup arm *needs* anti-skating. I don't see how it is debatable.
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mzil
post Nov 6 2013, 05:15
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AR XA.
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claudiod
post Nov 6 2013, 09:37
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QUOTE (mzil @ Nov 5 2013, 17:07) *
QUOTE (claudiod @ Nov 5 2013, 07:59) *
Now, I am still wondering why only the 45rpm and not the 33rpm were damaged (both were played on the same old mono turntable for 30+ years), and why only half side of the wave is damaged. Probably due to mechanical reasons such as different speed and centrifugal force?


Playing records at 45 RPM instead of the slower 33 causes more groove wall friction and heat, which over time will damage the vinyl surface, especially if the stylus has an incorrect tracking force, alignment, is chipped. worn down, caked with dirt, mono stylus use on stereo LPs, etc.. This problem is exacerbated by repeated playback and turntables that have an "auto repeat" function that are left to re-play the same side over and over again was not uncommon in many designs. As an analogy, if you rub your hands together slowly [33 RPM] there is no perceptible heat build-up, but if rub your hands together quickly [45 RPM] you can warm them up, due to the friction.

As for one channel being more damaged than the other, I suspect that's because of skating force. This lateral force applies more pressure against one side wall than the other. To the best of my knowledge your PL-990 turntable has no "anti-skating force" mechanism to neutralize this imbalanced pressure [although as I suspected the major damage was done previously during earlier plays, not your current playback, so swapping the TT with one with an anti-skating mechanism wouldn't help these records. Sorry.]

P.S. I've owned some top-flight TTs without any anti-skating mechanism, BTW. It is a relatively mild and usually inconsequential force, so the need to neutralize it is debatable, but when there is an issue, such as the problems I mentioned above (e.g. an incorrect, downward tracking force), it explains why the deformation is skewed toward one channel (one groove wall) more heavily than the other. Its primary importance is to ensure that when the needle is lifted from the grooves (either intentionally by the manual cuing control, or accidentally due to a very large warp in the record which launches the cartridge off the surface), that it returns down to the same groove, instead of skipping a groove or two.


It's not one channel damaged more than the other. It's half side of the wave in each channel which is damaged (the negative pressure side).

However I agree with all the rest of your analysis. And yes, the records where damaged by the previous plays, not by the current turntable.

This post has been edited by claudiod: Nov 6 2013, 09:38
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cliveb
post Nov 6 2013, 09:43
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QUOTE (mzil @ Nov 6 2013, 04:15) *
AR XA.

The AR turntables used the torque of the wires leading out the back of the pickup arm to impart some degree of anti-skating. It was a hopeless arrangement, no way of calibrating it, and rearranging the routing of the wires to try and adjust things was completely hit-and-miss.

The AR turntables were nice, but the pickup arms on them were pretty ropey. Loads of people have replaced the arm with something better, eg. Rega RB300, Mayware F4, etc. I modified my own XB by milling out the arm bearing and installing a Hadcock.
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mzil
post Nov 6 2013, 19:09
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QUOTE (cliveb @ Nov 6 2013, 01:43) *
QUOTE (mzil @ Nov 6 2013, 04:15) *
AR XA.

The AR turntables used the torque of the wires leading out the back of the pickup arm to impart some degree of anti-skating. It was a hopeless arrangement, no way of calibrating it, and rearranging the routing of the wires to try and adjust things was completely hit-and-miss.

And that would be because this "hopeless arrangement" you speak of, imparted by any torque from the exiting tonearm wire twist (acting as a sort of "anti-skating force spring") was completely unintentional. The fairly detailed XA instruction manual makes no mention of these wires purposefully (or accidentally, for that matter) serving in this capacity. All that it says is "Check to see that the wire at the back of the tonearm is formed as shown in this photograph. If not, gently bend it to the proper shape". End of story. The XA service manual similarly makes no mention that the tonearm's exiting wires serve any "anti-skating torque function", and furthermore explains in more detail that the wire should be arranged to smoothly loop around as it descends down to its rubber grommet in the XA's top plate, without kinks, as pictured in the instruction manual, for a specific reason:

"to allow free motion to the tone arm." [emphasis mine]

This common notion, I often see, of the XA's wires providing intentional "anti-skating torque" is purely the fanciful conjecture of some reviewers, hobbyists, and end-users. The real reason the XA didn't have any anti-skate mechanism is because the chief designer, Villchur, didn't believe the pros outweighed the con's, and he's not the only top-flight TT/arm designer with his view, by the way. [Although it wouldn't surprise me if after many years of being bombarded with questions about it, AR eventually gave in and simply endorsed this longtime rumor as being "true", simply to get people off their backs; I know of at least one other high-end TT manufacturer which did exactly that.]

This post has been edited by mzil: Nov 6 2013, 19:24
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mzil
post Nov 6 2013, 20:42
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QUOTE (claudiod @ Nov 6 2013, 01:37) *
It's not one channel damaged more than the other. It's half side of the wave in each channel which is damaged (the negative pressure side).

Oops, sorry. Got it. It's not skating or anti-skating then. I'm confidant it is that the damaged records had a history of repeated plays on a mono stylus, as I said earlier. Not good.

Mono styli are quite comfortable moving laterally, left to right, it's what they do. They were never designed, however, to move diagonally up and to the left vs. diagonally up and to the right, [which is how our stereo 45/45 LP records encode the L and R]. They get into trouble, distort, and damage the groove surface when they are asked to move, in any shape or form, vertically, in addition to the easy part, horizontally, in attempting to play a stereo LP. If their reluctance to move, say upward, is greater than their reluctance to move downward, then that would cause a deformation to only one side of the wave form, in both channels, which is what you describe.

This explains how our 45/45 system works.

This post has been edited by mzil: Nov 6 2013, 20:45
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cliveb
post Nov 6 2013, 20:45
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QUOTE (mzil @ Nov 6 2013, 18:09) *
This common notion, I often see, of the XA's wires providing intentional "anti-skating torque" is purely the fanciful conjecture of some reviewers, hobbyists, and end-users. The real reason the XA didn't have any anti-skate mechanism is because the chief designer, Villchur, didn't believe the pros outweighed the con's, and he's not the only top-flight TT/arm designer with his view, by the way.

Well, you obviously have some kind of authoritative knowledge here, so I defer to you.

But if, as you say, the AR turntable *deliberately* didn't have any anti-skating, then this just reinforces my opinion that it was a superb turntable compromised by an inadequate tonearm. I stand by my statement that a pivoted pickup arm (with overhang - I'm not aware of any pivoted arm design without overhang) *must* by the laws of physics impart an inwards force on the stylus which *should* be compensated for.

I am curious as to why Edgar Villchur believed the cons outweighed the pros. Could it have been that he feared many users would fail to adjust it correctly, and therefore decided to avoid the issue? You clearly know the history, so perhaps you can enlighten me.

Out of interest, what other pickup arm designer shares this view? Which other high-end arms omit anti-skating?
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mzil
post Nov 7 2013, 18:28
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Just to be sure all of our fellow forum readers, some new, are on the same page, I'll start with some basics:

"Skating", also called lateral thrust, is a tendency of a pivoted arm's needle (stylus) to be drawn inward towards the center spindle, as it rakes through the record's groove, due to the frictional drag pulling on it not being exactly 180 degrees away from the pivot point. The drag force is tugging at a slight angle towards the center of the record. Headshells, or more specifically the cartridges they hold, are slightly cocked toward the center (from a bird's eye view), at this "offset angle", to improve their tangency to the record groove.

The skating force puts undue pressure on the inside stylus edge, which is said to induce uneven wear, over time, both for the diamond tip and the records played. It furthermore reduces the level at which mistracking starts to occur, the point where the modulation of the groove is so large that the needle looses contact with the groove walls and is bashed about, wall to wall, which besides sounding distorted and nasty, causes irreparable harm to the vinyl, possible even from only one play.

"Anti-skating", abbreviated as AS, also called compensation bias by the British, counteracts the skating force by applying a constant, "equal" force in the other direction, away from the center spindle, usually with a spring or a counterweight dangled on a thread. All great in theory, but now let's look at the dark side.

First off, skating force, which is directly dictated by the frictional drag, is not constant at all; it varies greatly due to many factors such as the groove radius (distance from the center spindle), record speed, condition, and the modulation level of the particular musical passage being played. If, hypothetically, one sets their AS so as to play the most demanding, highly modulated torture track on their Hi-Fi News test record, then guess what? They will have set their AS so high that the pressure applied to the outer groove wall, on normal musical passages, exceeds the unwanted pressure they would have had on their inner wall, if they hadn't used any AS in the first place! They would then be wearing out their records and needle on the outer side edge, and at a faster pace, than using no AS at all! So you can't have both "best tracking of very loud, demanding passages" and "minimizes record/stylus wear"; it's one or the other. Applying some "ball park" value is the approach some take, but not everyone even agrees any AS should be used at all.

Some people, including the chief designer at VPI, Harry Weisfeld, [who makes some "class A" TT's that cost more than 100X that of the AR XA/XB!] claim that even the best of AS designs, even his own company's, cause audible problems under some scenarios. As one example, when you play a record where the center hole has not been properly punched out at the true center of the actual groove pattern, a not uncommon occurrence, then this causes one's tonearm to sway in and out, per rotation, and the friction of the counterweight's thread scraping back and forth over its post (recurring every 1.8 seconds at 33.33 RPM), might cause a noise which travels down the arm [or causes the arm to resonate/"sing"?] which is transmitted to the pickup. [I'm not claiming this. I don't really know. But I've heard the gripe from others.]

From VPI's FAQ's page:

"QUESTION- DO I REALLY NEED TO USE ANTI-SKATE

ANSWER- Most times NO! Some cartridge manufacturers are happier if you use anti-skate, such as Sound Smith's Peter Lederman, who believes in the sonic and mechanical advantages of it. At VPI we can hear it working, so we do not use it, and not just ours - we can hear them all working, as the center hole of the record is not dead center. This causes the anti-skate mechanism to pull and release the arm as it is doing its job."

Some posts, in other forums, mention the AR XA's designer, Villchur, supposedly has something written in Stereo Review magazine about his specific thoughts on AS, but I have not found the actual, original article, yet. Hopefully, I will get back to you if I am successful. As best as I can tell, Sound and Vision magazine, their descendant, doesn't archive all their earlier work, but I haven't given up just yet!

Considering I was the only one here who thought the OP's problem was related to AS, and I later retracted that, I'd suggest starting a new thread should you wish to discuss AS any further, since it is off topic at this point.

This post has been edited by mzil: Nov 7 2013, 19:11
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