Oh Greg, I have a thousand things to pick your brain about (I knew about CED being a vertical modulation and would LOVE to get into finer details of it with you, as I'm an "obsolete technology" junkie across the board)! I knew you'd come in with a bunch of relevatory and reliable information, and you have my thanks. This hit the spot.
So what I'm understanding is that every time the groove modulates away from its silent center, it is showing the needle to yet more lateral tracking error (Mikey Fremer, Art Dudley, and all those guys call it azimuth -- you know buzzwords fly around the office in America's corporate state! What do they know, anyway?). But because the overall phase of the groove is typically zero (except for the universal cut, but we're only talking about strictly lateral here), the convex wear on both sides of the needle is typically even, and the louder the record, the more safely shaved off the needle becomes. It seems like a pretty good system, if this is true, since the higher modulation exerts more force against the needle, so it is receiving more severe blows from the needle as it passes each ridge. So the more severe the groove works the needle, increasing the prospect of damage, the better-suited that needle becomes along the way. Pretty nifty! It's obvious I should clarify things real quick: to say vinyl could never wear a diamond is to say rocks can't be cut by water, which we all know isn't true. Every time I've said it, I have meant that a modern vinyl record would never substantially wear a modern diamond stylus within the confines of recommended use, which is to say that the cantilever suspension gives out way before the stylus starts to see any wear. I should've pointed this out all along; my apologies for any confusion. I should also point out that while my intention was to illustrate provable damage to modern vinyl records by playback with modern lightweight tonearms, the truth is that "negligible" doesn't even scratch the surface (so to speak, ha ha) -- in my example, a locked groove left playing for 5 hours more than once resulted in audible frequency changes. At 33.3 rpm, this represents 20,000 plays! So obviously, this kind of wear doesn't really translate in the real world. Again, my point was only proof that such wear does exist, and is measurable. Regarding DD's, Pathe's, and the virtual absence of LTA as a mitigating factor, you have pointed out all the same things I've pointed out. I did say that there is some error with the DD machines, but that it made no difference to the playback characteristics. I didn't point out that the arc was reversed, but it brings up an interesting point: Edison could've easily included one more extension to the tonearm suspension that would've given him bona fide linear tracking, i.e., zero lateral tracking error. It is my belief that he knew this and chose not to, for a few reasons. One, with a feedscrew driving the tonearm, it was not necessary to optimize skate/anti-skate issues for playback reasons. Two (and this one's a stretch), the reverse arc puts the lateral tracking error at the end of the disc towards the outside (I'm not sure how to say this correctly in technical terms), the way it is at the outside edge of the disc on a standard back-pivot tonearm, increasing the amount of skate force at the inside of the record -- certainly handy to ensure a quick skate towards the label after the groove ran out to trip the Duncan stop, though this would obviously have been an added bonus, not an initial design function. But most importantly, it sounds like exposing a rotating profile to the record when using perfectly conical or spherical stylii would be a GOOD thing -- that while making no difference whatsoever to playback characteristics, it offers a self-refreshing contact point on the stylus itself, probably adding substantially to the life of the stylus. It would certainly stand to reason. And with these two systems, we're talking about a situation where the stylus is custom-ground for the groove to begin with, that the fresher the stylus, the more contact area, so giving the groove the freshest stylus profile possible across the record's total surface seems like a real plus! All this said, Pathe's and Edison DD's are both still susceptible to damage from playback. I've found that on those 16" 120rpm Pathe's I recently got, highly modulated grooves at the end of the music, near the label, get rather ratty sounding, sort of blast-y. And I'm doing electrical transfers at 16-33rpm, so I know I'm getting exactly what is left in the groove. I can't imagine the Pathe system was able to completely avoid having the stylus leave the groove on loud, high, long notes (say around 1KHz to 4KHz), and as it would land on the other side of the 'hill', beat up the shellac as it went (though I can't say this is something I've seen much evidence of, outside of these 16" 120rpm discs, if that's even what it is). With so much less modulation on DD's, I'd think this particular problem was a non-issue for them (and I've certainly never heard a DD that blasted on loud, high notes like a standard lateral disc), but I wonder just how many times a new DD could be played by a new stylus in a DD phono before audible wear would appear. Would they really wear the diamond out first? Thanks for all your invested time and shared wisdom, Greg. Best, Robert ----- Original Message ----- From: "Greg Bogantz" <gbogan...@charter.net> To: "Antique Phonograph List" <phono-l@oldcrank.org> Sent: Thursday, March 06, 2008 3:09 PM Subject: Re: [Phono-L] Shellac records and damage from steel needles > Well, Robert, you make some good points in this discussion. But you > are in error on some as well. First, what you term "azimuth" error is > more commonly called "lateral tracking angle error" or LTA by the tonearm > engineers. It was widely discussed and debated, particularly at the dawn > of the stereo LP with many learned papers written about it in the audio > engineering press. This tracking error became more of an issue with > stereo records because it is associated with a slight phase misalignment > of the two walls of the groove (thus the two stereo signals) as the > cartridge tangency changes. (This is a separate issue from vertical > tracking angle error VTA which was also an issue with stereo records but > has no significance to lateral monophonic recordings.) The result of a > lot of "sturm und drang" over LTA error was that, yes, it exists, and yes, > it can be reduced to a minimum with the choice of the proper offset angle > of the head of the tonearm as a function of the distance of the tonearm > pivot to the platter spindle. You are correct that the shorter this arm > pivot to spindle distance, the more the LTA error. You are also correct > that this error results in the steel needle turning with respect to groove > tangency as the record is played from one diameter to another. It is > reasonable to assume at first blush that this turning will present a sharp > edge of the previously flatted side of the needle to the groove wall and > thereby do some gouging of the wall. However, you are forgetting that the > groove is not without wiggles in it which represent the audio modulation. > Which means that the groove wall is continuously changing in its > instantaneous tangency with the needle. This means that the needle does > not have purely FLAT spots worn on its sides, but rather slightly curved > (convex) spots as the sharp edges are continuously worn down by the > modulation in the groove. The higher the modulation, the more this > curvature will present. Therefore, the additional slight turning of the > needle in its tangency with the groove caused by LTA error is probably > insignificant in its effect on groove wear as the needle doesn't present > but statistically a very tiny amount of additional rotation beyond the > curvature of the flats caused by the previous record modulation. In other > words, the effect of LTA on causing additional record wear is probably > negligible. The effect might be more noticeable on records with very low > modulation such as some classical chamber music or similar. > > Your statement that vinyl record cannot and do not wear diamond styli > is not correct. I was engaged in doing a lot of record compound wear > testing when I worked at the RCA Records manufacturing labs in > Indianapolis. We were developing two radically new record compound > formulations at the time. One was needed for the new CD-4 quadraphonic > audio records which contained supersonic signals up to 45kHz and the other > was needed for the RCA Capacitance Electronic Disc (CED) video disc system > that was still in development (it was vertical modulation, you might be > interested to learn). Consequently, we had installed a scanning electron > microscope (SEM) to evaluate the effects of wear both on styli and on > records. The SEM allows remarkably detailed views of the minutest surface > irregularities with extremely high magnification and extremely long depth > of field view (sharp focus over a wide range of depth in the specimen) > that is not possible with optical microscopes. I did wear testing of the > audio record formulations using several stylus shapes and tracking forces > that represented the typical users of the day, about 1975. We checked the > amount of wear that could be seen at intervals of 25 plays from 0 to 200 > plays using players operating typical high quality stereo cartridges > operating elliptical diamond styli at 2 grams, Shibata diamond styli (line > contact) operating at 2 grams, and conical diamond styli operating at 5 > grams which represented a good consumer type player of the day. The > results were frightening! The typical stereo vinyl record compound > exhibited quite noticeable "trenching" of the sidewalls of the groove with > the 5 gram conical in as little as 25 plays. When auditioned, especially > after 50 plays, these records sounded well worn with much noise and > crackling. The 2 gram elliptical fared better, but at 100 plays it > produced noticeable trenching as well. The Shibata at 2 grams would show > very little wear of the sidewalls at 200 plays. > > What's more pertinent to this discussion, however, is that the styli > had to be changed at regular intervals as they ALSO exhibited noticeable > flattening of their contact surfaces. I could get upwards of about 1000 > plays from the 5 gram conical diamonds before I decided that they had > gotten too flatted. And, as I have stated above, the "flats" weren't > actually flat but rather broadly convex flatted portions at the contact > points. 2000 to 3000 plays were about where I changed the 2 gram > ellipticals, and the Shibatas could last for 5000 plays or more. And > these vinyl record formulations contained no abrasives. But they DID wear > the styli. > > Lastly, I think you need to take another look at the LTA issue with the > Edison DD player. Yes, the Edison tonearm is pivoted in front of the > pickup as opposed to being pivoted at the back as with all conventional > lateral players. But it is still a pivoted tonearm and it DOES exhibit > LTA error. It just occurs with the reversed tangency arc to that of the > back-pivoted arm. In the typical DD player, the LTA is fairly low at the > outside record diameter but becomes quite high at the inside music ending > diameter. In fact, the LTA error was deliberately used to advantage in > the development of the Duncan electric stop. The fact that the LTA is > very high at the inner diameter of the DD player causes the stylus to > skate toward the spindle with considerable force. When the stylus falls > out of the groove at the inside end of play, the stylus and weight > assembly swing inward until the weight limit pin hits the limit loop which > makes the electrical contact that the Duncan stop relies on to close the > circuit and operate the solenoid which stops the DD motor. If there were > no or very little LTA error, the skating force would be minimal and the > weight would not swing to the edge of the limit loop. > > Of interest here is that this LTA error on the DD player is basically > irrelevant, assuming the stylus is in good condition. The Edison as well > as the Pathe system relies on the conically shaped stylus tip sitting > directly on the bottom of the groove to properly trace the vertical > modulation. It can do this properly REGARDLESS of the tangency of the > pickup head to the groove. You will note that some record players > designed to play both vertical and lateral discs with their adjustable > reproducers often present the Pathe stylus to the record groove at quite a > radical angle to the tangent. The Brunswick Ultona comes to mind. Yet > the system works because the LTA is irrelevant for purely vertical > modulation. Also note that Pathe tonearms are often quite short. But the > LTA that this causes poses no problem to the reproduction. > > Back to the case of record wear: The Edison DDs were specifically > designed to have quite a hard surface compared with the shellac material > that was used in lateral records of the day. That's why Edison chose the > condensite material. The playback theory of the lateral records was to > have the abrasive in the record material (which by the way was not diamond > dust which was much too expensive - the abrasive was a combination of the > cheap clay filler and pulverized limestone) wear the needle rapidly so > that the "flats" developed which VASTLY increased the contact surface area > and thereby quickly reduced the pressure on the sidewalls which reduced > further record wear. If you were to play a shellac record with a new > steel needle every few turns of the record (quite a tedious operation), > you would find the record very quickly wearing out because you would not > be allowing the use of a properly worn in steel needle with the right size > flats. You may have noticed that some records sound particularly noisy > during the first few revolutions of the starting grooves. This is because > the use of a new steel needle causes excessive wear in this portion of the > record. > > Contrary to this theory of operation, Edison wanted to wear the diamond > stylus rather than the record surface. So he used a stylus shape that had > a fairly big radius, AND which sat on the groove bottom with a large > percentage of its circumference supported by the matching radius in the > groove. This spread out the high tracking force over a fairly large > contact patch at all times. There was no need to wear flats on the > stylus. Note that even if the point of tangency changes due to the LTA > error of the Edison tonearm, the spherical stylus tip merely rotates in > the groove but STILL presents the same curved contact surface with the > record which does not have any additional effect on record wear. The > choice of the condensite material was such that it's elastic yield point > (permanent deformation) was higher than the pressure presented to it by > the rounded stylus sitting in the rounded groove. All is well and good > until the stylus becomes chipped. When this happens, the sharp edge of the > chipped area presents a much smaller contact patch to the groove which > very quickly yields the condensite under this very high localized pressure > and results in a very visible brownish-looking scratched appearance. The > record surface has now been permanently damaged and the record will play > that area with much increased noise. Regardless of whether you call it > wear or damage, it's been ruined. > > Greg Bogantz
