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Fun analogue question


maxg

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I am in the midst of a debate with a fellow audiophile which we have boiled down to the following:

Which is more damaging to a record?

Arm apparent mass plus cartridge mass plus fixings 28 grams, tracking weight 1.

or,

Arm apparent mass plus cartridge mass plus fixings 18 grams, tracking weight 2.5.

We are at complete loggerheads on this one. Thoughts and reasoning anyone?

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Without knowing the compliance of the cartridge it won't be possible to accurately answer your question. A stiff compliance on an arm with more mass will cause more wear.

Highly polished styli cause less record wear in either case.

None of this matters much if the record is not cleaned properly.

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Mark,

You do realize, don't you, that suggesting to simply observe and measure results makes you a heretic.

In one of Sir Francis Bacon's books published early in the 17th century he reprinted a passage that he had found in the records of a Franciscan friary. This passage from 1432 concerns how a group of friars tried to figure out how many teeth a horse had in its mouth. It is a good example of the “old” way of doing science. The passage goes as follows: In the year of our Lord 1432, there arose a grievous quarrel among the brethren over the number of teeth in the mouth of a horse. For 13 days the disputation raged without ceasing. All the ancient books and chronicles were fetched out, and wonderful and ponderous erudition, such as was never before heard of in this region, was made manifest. At the beginning of the 14th day, a youthful friar of goodly bearing asked his learned superiors for permission to add a word, and straightway, to the wonderment of the disputants, whose wisdom he sore vexed, he beseeched them to unbend in a manner coarse and unheard-of, and to look in the open mouth of a horse and find answer to their questionings. At this, their dignity being grievously hurt, they waxed exceedingly wroth; and, joining in a mighty uproar, they flew upon him and smote him hip and thigh, and cast him out forthwith. For, said they, surely Satan hath tempted this bold neophyte to declare unholy and unheard-of ways of finding the truth contrary to all the teachings of the fathers. After many days more of grievous strife the dove of peace sat on the assembly, and they as one man, declaring the problem to be an everlasting mystery because of a grievous dearth of historical and theological evidence thereof, so ordered the same writ down.
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Well, I've no bone to pick with good measurements. However, my gut tells me "If it sounds good, it IS good." both for the record and the ear. Hard to imagine that optimum sound does not=mimimum damage from any setup (at least as little as that particular setup is capable of).

Dave

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OK - assume all other variables equal. Compliance - say 12 - somewhere in the middle. Tip - whatever you want - same for both.

Assuming that the manufacturers were competent, these two styli could not share the same value for compliance. The 18 gram rig would need a higher compliance, the 28 gram, less.

But for arguments sake, let's think about it. Maybe we can count the horse's teeth without looking...

The compliance is how easily the vinyl is able to presses the stylus out of its neutral position. The compliance also acts as the mechanical damping between the pressing vinyl and the apperant mass of the cartridge. The compliance needs to be a value that allows the stylus to take the brunt of this pressing and not allow it to pass to the apperent mass of the cartridge.

If you take the compliance to be the same in both units, is it possible to find a value where the effect of the mismatch is the same for both? The effects are of opposite sign, so maybe, no. Even if the shared compliance value was tweaked so that even the different effects could be offset such that the overall mechanical effect was the same, this would just leave the tracking force to determine the remaining macro difference.

But let's look at just compliance for a minute. Assuming that the matching of apperent mass and compliance is done properly, which is harder on the record; greater appearent mass and less compliance, or less mass and more compliance? Clearly the former has the vinyl having to press harder against the more resistant stylus.

But that is assuming the same tracking force. But the tracking force is only having its influence in the vertical plane (and restricted to a line arc of that plane), whereas the compliance is in the lateral plane and includes horizontal and vertical components

So, let's go back to the original:

Arm apparent mass plus cartridge mass plus fixings 28 grams, tracking weight 1.

or,

Arm apparent mass plus cartridge mass plus fixings 18 grams, tracking weight 2.5.

The stylus will be resisting the press of the vinyl, and it is doing so in a partially confined geometry. Although the groove is open forward and back, the mount of the stylus prevents going there. The sides confine the stylus with vinyl walls, so the only remaining direction is vertical up.

Now the "V" shaped groove presses not strictly lateral but has a vertical component as well. Part of the verical component carries the more mono elements of the signal. But the stylus may also misbehave and displace upwards when the angled vinyl surface presses laterally producing an error not intended as part of the signal. I would expect some vertical plane position error as the stylus might tend to try to take the y axis component upward instead of sideways to some degree - this is the only degree of freedom the stylus has to go from confinement and this degree of escapement error must depend somewhat on the compliance (too much causes it) and the tracking force (too little suggests the upward direction to escape it). This translation of lateral to vertical vector component would convert some of the stereo effect to more mono playback (up and down motions vs side to side).

So, using my teeth of the horse method of thinking, I would favor the 18 gram / 2.5 gram arraingement.

To use Bacon's method, you might test for stereo separation differences. You can do this easily by using a test record, or an old TV. The back of the tube has two windings around it. One is the horizontal scan and the other is the vertical scan. Disconnect the wires to the coils and hook them to the right and left channel outputs of an amp. If you have the channel phases hooked up as "standard", an in phase stereo signal will form along a line from lower left to upper right (out of phase upper left to lower right). Otherwise reverse the wiring to one of the coils. Play music, watch the screen... mono signals should be round, stereo signals will be elipses. Many lower frequency signals will form interesting lissajou figures.

Lissajous? see here... http://www.ngsir.netfirms.com/englishhtm/Lissajous.htm

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Paul,

Interesting take. Mine is a bit more simple - but not necessarily correct:

I would work on the assumption that the greater the lateral displacement within the groove the more damaging to the vinyl the setup is.

In the above example it is the mass of combination of arm, mountings and cartridge that would act to exert force on the groove wall - the wall is having to work that much harder to keep the needle in the groove.

This would mean that the greater downward pressure (tracking weight) is actually working for you as it presents a greater force keeping you in the groove.

Therefore - the greater the tracking weight and the lower the overall mass the better.

This is somewhat counter-intuitive but I think it is actually correct.

I am not sure how the compliance would fit into this equation. In some ways (where the movement from centre is low) the higher the compliance the better but at some point it would tend towards its limits and there would be a snap back effect which could be more damaging than anything else. With a lower compliance we are, in effect, forcing the motion, as far as possible, to the main bearing of the arm itself. That does mean more mass displacement but it should be a smoother motion.

What is interesting is the looking at various manufacturers out there over the years we can see implementations that follow each and every combination of compliance, mass, tracking weight and so on - each with their own take on what is the best solution.

All in all it is not as straightforward as it might initially appear.

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Actually, I think the size of the excursions are normalized during the cutting process - large low frequency excursions are reduced and high freqs exagerated; this is the compensation for which the phono EQ reverses. What puts additional pressure on the stylus is large accellerations. This occurs much less with low frequency and much more with high frequency. I don't have the figure at hand, but I believe the linear speed of the stylus against the vinyl for high frequencies is about 15cm/s. Another way of thinking about it is that the amonut of vinyl wall that needs to be tracked for a high frequency is many times that of a low frequency. That's if they were recorded separatly, but in real life they are all superimposed into the same groove.

The very high accelerations comes from changing direction 30,000 times for a 15kHz frequency, for example. This is where the effective tip mass of the stylus comes into play, compliance, apperent mass, and the tracking force, too.

One way of thinking about the relations among apperent mass, compliance, and tracking force is to do thought experiments comprising the extreme cases.

Imagine a system where the compliance and apperent mass are maximized. This might be a stylus where the suspention mount was given a drop of epoxy and a couple of kilograms was added to the arm and balance. This would approximate an incredibly stiff stylus in the groove which would not want to move and would tear up the vinyl. Changes in tracking force would not make any difference until the weight was so great that the apperent mass was overcome and the stylus (actually the whole arm) began "tracking", but this would destroy the stylus, the mount, record, etc.

Imagine the opposite system where the compliance is absurbly high and the apperent mass is as light as a feather. At light tracking forces the stylus would probably hop the groove rather than track at all, then with more tracking force the stylus would track, but the whole arm and assembly would be vibrating with the stylus again likethe above example, although the record might survive.

Imagine the system where the compliane was near zero (epoxy mount) and the apperent mass was feather light. This just makes the conduction of vibration from the stylus to the arm and assembly that much worse, tracking force adjustments notwithstanding. Again, vibration of the whole arm assembly.

The only extreme case that looks like it might retain some proper function is where the compliance is very high and the apperent mass is very high. The only real issue then becomes whether the stylus will follow the grooves from the outer rim of the record toward to center, or if the stylus' job of displacing the mass is so difficult that the stylus just stays over one spot and hops the groove. I think some players actually use this kind of approach, but they use an auxiliary system to advance the stylus rather than depending on the outer vinyl wall to push it across the record.

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C&S, whereas I think greater tracking force is usually better for sound and wear due to better contact, I'm sure you must be joking.

Damage to the vinyl might be classified into a couple of forms.

1] There is the possibility with a dirty record of welding debris into the vinyl wall by the stylus (instantaneous temperature is close to 800 F). This is a permanent damage that would be heard in subsequent plays as noise, but I think one might hear it the first time as the welding of the debris entails the stylus encountering the debris (a noise signal) while pressing it into the wall.

2] There is the permanent reshaping of the track in the vinyl that can occur in various situtations, all of which would be possibly heard, as the stylus would be tracking into the mis-shaped vinyl as it performed the original mis-shaping on the first play.

3] There is the case where the integrity of the vinyl shape is breached - pieces chipped, sheared, plained, or otherwise removed from the wall or permanently deformed during playback. I have to believe that this would induce additional noise as the stylus traveled over and along the bits of loose vinyl being torn off, and there might be some audible effect to the stylus cutting through the wall surfaces rather than just sliding across them.

Now there is a difference between a first play and a second following shortly after... The groove when tracked actually does separate a bit as the vinyl is pliable. It takes the groove about 24 hours to recover and close back to its original geometry. Those that play a record over and over might well notice that the first play was the best, subsequent plays shortly after being degraded somewhat by the stylus tracking deeper into the groove - ultimately getting deep enough to begin dredging up the debris that resides in the very bottom of the groove that is never supposed to be tracked by the stylus. By then the record will have the familiar sound of a juke box where this happens all the time - Lots of bass and little high end.

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Paul,

Thanks for that excellent information which may explain why many of my visually shiny vintage LPs can sometimes sound so bad even after cleaning regimes. I have a rather large collection of both high quality LPs (many bought new or truly NM when purchased) and an even way larger collection of default LPs (inherited from various sources) and years and years of combing thrift stores for what appeared as NM and VG+. I play an extremely wide range of LPs from classical to jazz to latin and sometimes must play poor examples for their musical information which may be otherwise quite rare to find. To give a glimpse: recent exciting scores of obscure and impossibly rare LPs include Calcium Light (Gunther Schuller arranging and conducting the orchestral work of Charles Ives) amazing stuff, several LPs of obscure Indian music on Odeon (to be revealed at a later date), the spoken word and poetry with jazz LPs of Kenneth Patchen including his early readings from the Journal of Albion Moonlight. Also, even tho not quite so rare: Claude Debussy at the piano! via the Welte Vorsetzer. Given the wide range of material in my collection I would tend to think that the actual percentage of showcase audiophile worthy albums is relatively small, although I have enough to show off the system when needed.

Yes I was basically joking, I rarely part with musically interesting material however non-perfect, but do sell duplicates and stuff I am not interested in on eBay sometimes. One of the most "important" albums I have is the 10" SMC LP "Concerto in Percussion" (1947) Julio Andino and Jose Estevez. This album, even in mint condition, is 50% surface noise!!!, but is very rare and not to be reissued and is, arguably, the very first latin jazz masterpiece. Such was the low quality vinyl used by this legendary company in 1947.

To extract the best I can from this wide range of sometimes compromised material, I use a tri amp system with electronic crossover and an Aphex aural exciter. I currently use either an Ortofon MC20-superII or the Denon 103 as a workhorse.

PS. I just recalled what a revelation it was looking through the microscope attached to a Scully Lathe while a vinyl master was being cut. Wish I could see what was actually going on at that level of magnification with many of my problematic LPs. Your comments make me realize some of the possibilities.

C&S

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Unless you see visible scratches, smudges, and other stuff, I don't think one can tell whether a record is going to sound clean. I have some of my first records I bought in the late 60's that are still pristine after all this time; others had noise the first play that never went away.

The last album I bought was a used one at 1/2 Price Books. It is an old Jeff Beck album and I was amazed that it is dead silent clean.

I have a collection of 10 cartriges which I have ranked for quality by examining them under my microscope and measuring the coils with a multimeter. I use #1-3 (line contact styli) for special occasions on my cleanest favorite albums, #4-9 (elliptical styli) in rotation for everyday listening, and #10 has a simple spherical stylus - I use it as a "stunt cartridge" for experiments (with records I don't care about harming).

My turntable is an old Bang & Olufsen, so it only takes three seconds to swap cartridges; they all have the same physical geometry and weight.

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Easy. It's contact stress, period. Unless the mass and cartridge compliance is waay out of the commonsense range it is not even part of the equation. A high mass arm requires a low compliance cartridge to keep the resonant frequency in the 7 to 10 Hz range. So, if you're close to that, any tracking errors from a mis-match drops out and contact stress rules. Note that no information about tip shape is included and thus is assumed to be identical for each cartridge.

The 2.5g tracking weight is worse due to the stress in the vinyl.

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Yes, contact stress rules. That's why I mentioned the different stylus tips I use. The simple one is "spherical", which really means conical with the sides curving to the point. The contact on the groove wall is small, almost a point contact. This concentrates the force to a small area and is relatively tough on the vinyl. The elictical ones has a wide radius across the groove and the contact area is greater - forms an elongated vertical contact area against the groove wall. This provides more surface to distribute the force and also improves the left right phase coherence by reducing the degree to which the left and right channels trade being in advance of each other every time the stylus reverses direction in the groove. The line contact styli are very similar in geometry to the original knife edge that cut the records in the first place. Their contact with the groove wall comprises a line contact along almost all of the vertical side length of the stylus. The channel phase coherence is very improved, and most of the groove wall is used to bear the tracking force.

Since the contact stress is based on the amount of groove surface being touched by the stylus (the more the better, less force per area), the line contact is least stressfull and has the most fidelity, the eliptical have less area to work with and provide more contact stress, the spherical stylus does the most potential damage. This also means that the line contact dtylus may track a little heavier without harming the record.

The amount of damage from tracking force variations depends on the spec for the cartridge/stylus. The suspension of the stylus is made to maintain correct geometry within a tracking force range. Tracking too lightly allows the stylus to skip over some groove modulations, and the loss and recovery of contact is harder on the vinyl than a constant contact.

There are lots of high end cartridges/styli that are designed to track pretty heavy (couple of grams), others are designed to track light (1gm is the lowest I've seen). All mine are designed to track at 1gm, but I like it a little more at about 1.25gm. I think if you stick fairly close to the manufacturers' recomendations even a couple of grams won't really hurt the record if the cart/stylus is designed to operate like that.

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