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How to determine condition of diamond on stylus, On a AT-90 cartridge
Jenni28
post Jan 23 2011, 22:55
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Have a Technics turntable - Mod. SL-B1 w/ a Audio-technica AT90 cartridge. Not sure if needle / stylus is replaceable on that model? Appears not, so raises issue of quality of cartridge / stylus, in my mind.

Main Question: Determining condition of the diamond (tip) on diamond stylus.
I'm digitizing some LPs. Seems to play OK, but don't have anything to compare to & haven't listened to LPs in so long, can't remember what sounds good or not so good.

I looked at some (hi power) pics of diamond styli here.
Have a much lower power geology / rock magnifier. Looking at the AT90's stylus w/ strong light, appears much same as pic on linked page - just less magnified. Diamond tip at my lower power appears sharp - but at that power, who's to say?

Son gave me the Technics, after I dug out my old Dual & discovered, years ago when he was a teenager, he & buddy "borrowed" the Pickering cartridge out of my Dual. biggrin.gif

Looked up current prices of AT-90 cartridge with stylus (whole cart) & is only $29 at Vintage Electronics.
Prices may have DROPPED on cartridges vs 1970's - but the Pickering I bought then was ~ $50. It was one of V15 models (don't remember exact one) - that an old Pickering needle I have fit in (DAT 2). BIG diff in price. Some current prices on the very lowest end V15 cartridges (sans stylus) are $30. I'm sure my old Pickering would have been mid priced one in that V 15 line.

So, don't know much about quality of that cartridge, or if it's even matched to this Technics table.

Here's specs on AT 90 cartridge from a retailer - assume came from mfg -for what ever mfg specs are worth smile.gif
QUOTE
AT-90CD
Dual Moving Magnet Cartridge

* Stylus Type: Bonded round shank.
* Stylus Shape: Conical.
* Cantilever: Alloy tube.
* Frequency Response: 20 Hz. - 20 kHz.
* Output Voltage: 3.5 mV at 1 kHz, 5 cm/sec.
* Channel Separation: 24 dB. at 1 kHz. / 21 dB. at 10 kHz.
* Channel Balance: 1.5 dB.
* Vertical Tracking Force Range (Grams): 1.0 grams - 1.5 grams.
* Recommended Load Impedance: 47,000 Ohms.
* Mounting: Universal mount system incorporates Standard 1/2" (12.7mm) mounting centers and P-Mount Applications.

Thanks.
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DVDdoug
post Jan 24 2011, 19:42
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It wouldn't hurt to replace the cartridge. The elastomers have hardened over time too, although if it sounds OK... ???

QUOTE
Prices may have DROPPED on cartridges vs 1970's - but the Pickering I bought then was ~ $50.
There are still some VERY expensive cartridges, but I assume most people (including me) have given-up on perfecting the sound of vinyl. I don't see the point of spending more than the cost of Shure's best (~100 USD) when it's never going to sound as good (to me) as digital.

This post has been edited by DVDdoug: Jan 24 2011, 19:51
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Jenni28
post Jan 24 2011, 22:00
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Thanks. You talkin' bout the elastomers in the vinyl?

Probably won't replace ANY cartridge until find out if can fix the Technics, or drag out my old Dual 1218. Or get another table. Last time I messed w/ the Dual, lubricated it, only to discover son had pilfered the cartridge years ago. Back in the closet. Oh well, he's a great son. It was much more complicated taking that turntable apart than I ever imagined, even for someone used to taking apart / reassembling just about everything.

No, doubt I could detect noticeable diff in a $50 - 100 cartridge & a $200 - 300 one. Or care. I'm sure some have very sensitive, discerning ears, or at least they convince themselves they can tell a large diff in their top end phono cartridge.
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DVDdoug
post Jan 24 2011, 22:56
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QUOTE
You talkin' bout the elastomers in the vinyl?
I'm talking about the stylus support/suspension. (It's normally part of the stylus assembly, so if you replace the stylus all of the moving parts get replaced.)

This post has been edited by DVDdoug: Jan 24 2011, 22:57
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Jenni28
post Jan 28 2011, 02:22
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I found a way to look at the diamond tip using an inexpensive microscope. Depending on size of scope & specific cart, might not fit. This one did.

Used a mini flashlight to add more light on the tip. Don't need extremely high power to see some detail. Of course, they make magnifiers specifically for styli.

As for my AT90 - the stylus support arm was bent about 20 deg. near where it's attached to the stylus housing. I'd only played a couple records since digging this out of closet. I'm not sure how it even played - but won't be using that stylus, for sure.

I also had an OEM Pickering DAT2. The quality of DAT2 was quite a bit better under the scope than the AT90. That's probably why an AT90 cartridge is only $25 - 35.
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ramicio
post Jan 28 2011, 16:42
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Just wondering, how does a diamond wear out from vinyl? I can understand the moving piece of a stylus wearing out, but I can't see how the hardest natural substance known to man can wear out from a really soft plastic.
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Arnold B. Kruege...
post Jan 28 2011, 17:15
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QUOTE (ramicio @ Jan 28 2011, 10:42) *
Just wondering, how does a diamond wear out from vinyl? I can understand the moving piece of a stylus wearing out, but I can't see how the hardest natural substance known to man can wear out from a really soft plastic.


The more general question is how do soft materials wear out hard tools?

We all know that it happens all of the time because cutting soft wood eventually dulls hardened steel saws, and cutting relatively soft food dulls hardened steel kitchen knives.

One source of wear is dust and other tiny hard items in the nominally soft material. The dust on records can include tiny particles of silicon oxide sand which is nearly as hard as diamond.

If you rub something hard against something soft, both sides loose or displace a little material. The ratio of material lost or deformed is inversely proportional to the hardness of the materials. If one material is very soft then it suffers most of the loss by far but there is still some loss from the hard object.

In the case of a stylus, wear on its tiny tip is balanced by the tremendous amount of plastic that it is rubbed against. All stylus wear is concentrated on a small area, while record wear is spread out over the length of the grooves on many LPs.

The standard causes of tool (stylus) wear are adhesion, abrasion, diffusion, oxidation. fatigue wear, and plastic deformation. They all apply to stylus tips to some degree.

Due to the tiny contact surface between the vinyl and the diamond there can be substantial heating, so this is not a room temperature process, but one that happens at temperatures that are high enough to temporarily liquefy a tiny area of the vinyl. This accelerates the wear.
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Jenni28
post Jan 28 2011, 17:44
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Arnold is correct. Another major cause of diamond wear is dirt / dust in grooves. Unless you REALLY clean LPs, there's always some microscopic (or nearly) dust. "Dust" can be clothing particles or extremely fine dirt particles - could be almost any mineral composition. Many rock (dirt) minerals have hardness value of 7-8, where diamonds are a 10 hardness.

That doesn't mean if you took a diamond ring & dragged it across concrete (w/ light pressure) that the diamond would never wear, just because it's harder than concrete. It would wear. Either way, if diamond styli didn't wear from playing records, there'd be no such term as a "dull needle / stylus." They'd last forever - short of damage to metal arms. Of course, that's not the case. That's why phonograph & styli mfgs always advise cleaning records AND stylus before playing.

Just cleaning a dirty record well, often reduces some crackling & clicks. some of those are from needle "jumping" over dust particles (which may be MUCH harder than vinyl), & some of the noise is from damaged vinyl.

I used diamond wet tile saw blades to cut ceramic tile. The diamonds are MUCH harder than the ceramic, but eventually the blade wears out completely.

This post has been edited by Jenni28: Jan 28 2011, 17:48
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ramicio
post Jan 28 2011, 18:18
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I forgot diamond doesn't like much heat and breaks down pretty quick when heated because of friction. If kept cool they might last forever.
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