Phonograph Stylus Wear Experiment

[ray_parkhurst]

None of my vintage AT cartridges have hard dampers, unless I don't know what I'm looking for. I'd assume that the cantilever would seem "stiff" if it were hardened, and there would be a severe sonic impact due to poor tracking, correct? If so, then I have not seen this in any I own.

 

[USER]

None of my vintage AT cartridges have hard dampers, unless I don't know what I'm looking for. I'd assume that the cantilever would seem "stiff" if it were hardened, and there would be a severe sonic impact due to poor tracking, correct? If so, then I have not seen this in any I own.

Which do you have? The higher end models that had issues are Japanese only imports, so, perhaps that has something to do with it. I see all sorts of corrosion on cartridges of all types on Japanese resale sites so there could be "something in the air" by the sea over there. I'm sure John's market in Australia saw more of those types. As I mentioned, my Signets from the late 80s are fine, and those are generally understood to be higher-end AT cartridges. The cheaper ones...well they are just cheaper so that's easier to see.

That said, for me, buying from Japan has been more hit and miss than it has ever been this past year. I try very hard to be patient and conservative but have had issues like the above. I have a Grace F-8L and a B&O SP-12 coming in that are hopefully in good shape. (I'm in the purchase my aesthetic favorites phase at this point.) My last purchase annoyed the hell out of me:

I may need to try the 180 then

I have asked myself what I would do if I found one at a good price. What a relief to say I'll just let JP get one and measure it! It is essentially a Signet so it should be OK I think.

 

[ray_parkhurst]

Wow, that 90 deg mounting is pretty obvious. On ellipticals it can be harder to spot, but OQA should have caught that one.

All my AT cartridges are 1980's elliptical and biradial P-Mounts, probably all 35-40 years old. No high-end stuff. I've never put together a full list but here's most of them:

LS350/LT NOS
ATL12E2 NOS
AT312HEP NOS (I have several)
ATN312HEP NOS (I have several)
ATN312EP NOS
Series V NOS and used (I have several)
Series VII NOS
SLT96E used
AT733 used
AT231LP used

None show corrosion on the cantilever. That type of corrosion is usually due to being in a condensing environment, either very high humidity or being moved from cold to hot without allowing for temp equalization.

 

[JP]

I have asked myself what I would do if I found one at a good price. What a relief to say I'll just let JP get one and measure it! It is essentially a Signet so it should be OK I think.

Can't that I've ever seen Signet DNA in an ML180.

None show corrosion on the cantilever. That type of corrosion is usually due to being in a condensing environment, either very high humidity or being moved from cold to hot without allowing for temp equalization.

Attics in Japan are very unfriendly.

 

[JP]

@BMRR(VE) will be doing the recordings of the STR100

At 192 (or better) I hope?

 

[ray_parkhurst]

At 192 (or better) I hope?

Well, that would miss the whole point of the experiment. The goal is to measure the stylus wear, not to make the best recording we can of the STR100.

 

[USER]

If you want full 3rd harmonic for the sweep you'll need to. 96 for full 2nd harmonic. But it's your experiment so do what you want.

 

[JP]

Well, that would miss the whole point of the experiment. The goal is to measure the stylus wear, not to make the best recording we can of the STR100.

I thought you guys wanted to measure harmonic distortion - kinda need the harmonics captured to do that. At 96k you'll get 3H to 16kHz and 5H to 9.6kHz.

 

[ray_parkhurst]

When I say "measure the stylus wear", it is a 2-pronged approach: shoot photographic images of the stylus tip and measure the size of the contact patches; and record a test record using the DUT and Reference styli and compare harmonic distortion changes over time. Correlation of these will hopefully give us some info on impact of wear to harmonics and some guidelines for replacement.

I do question the usability of harmonics above 20kHz. I would expect this depends on the response of the RIAA preamp used for the captures. We eliminate some of this by doing a comparative analysis so that the absolute levels are not as critical. How do you do analysis of harmonics that fall outside the RIAA curve? Capacitive loading would play quite a big role here as well. The comparative measurement (reference stylus on same cartridge, comparison vs test point, etc) helps calibrate this out, but what do you do on absolute basis? I suppose you could calibrate any system with a reference sig gen with output RC network to approximate the cartridge, then use that as a reference for the absolute measurement. Is this what you do? Or do you have a more (or less) elegant approach?

 

[JP]

I'd use a flat amp for the test record capture. I've not given the rest of it any thought beyond 'capture all the data that can be reasonably captured'. Part and parcel with trying to run an experiment before the objectives and methods are sufficiently defined.

 

[ray_parkhurst]

I had not thought much about it, but indeed the actual harmonics are being equalized by the RIAA, so the measurement result is skewed. Using a flat amp would eliminate the equalization and give a true reading of the levels. Good suggestion! Just need to use an amp that is flat up to 48kHz to ensure accurate capture across the Nyquist bandwidth. The flat amp approach would not only give a better readout of harmonics, but also a much higher number that would be easier to analyze.

When harmonics are quoted, they are of course given with the RIAA equalization in place. I assume it would be trivial to add this equalization mathematically to the output to give numbers that would correspond better to what would be quoted by mfrs, reviewers, etc, correct?

What gain would be needed? I suppose correct resistive and capacitive loading is required to get an answer that would be meaningful for comparisons. An RC is needed for the cartridge to be properly loaded, but would introduce some filter effects. Perhaps resistive to match the output, but no capacitor? I suppose the capacitive filter effect could be added mathematically along with the RIAA.

 

[ray_parkhurst]

Now come the practical difficulties. I need to make sure @BMRR(VE) has recording capability without RIAA, and that if so the line input has wide enough bandwidth. I suppose it would not make sense for a system with 96kHz sampling rate to not have the full 48kHz bandwidth, less IRF.

 

[Icewater_7]

Now come the practical difficulties. I need to make sure @BMRR(VE) has recording capability without RIAA, and that if so the line input has wide enough bandwidth. I suppose it would not make sense for a system with 96kHz sampling rate to not have the full 48kHz bandwidth, less IRF.

Given the cache of engineering experience within the ASR membership I would imagine someone could easily design and breadboard an opamp-based gain stage that has the needed specs.

 

[ray_parkhurst]

Is the 96kHz (or higher, 192kHz?) ADC a simple matter?

 

[Thomas_A]

The script gives opportunity to use flat or with RIAA. Not sure flat-amp is needed, but 96/192 kHz is good if you want 2H/3H up to 20 kHz.

 

[ray_parkhurst]

The script gives opportunity to use flat or with RIAA. Not sure flat-amp is needed, but 96/192 kHz is good if you want 2H/3H up to 20 kHz.

My concern is the lack of control and effect of capacitive loading above 20kHz. How many RIAA preamps are spec'd for accurate equalization up to 48kHz, or 96kHz? Using same loading and preamp and doing comparisons to know deltas before/after wear is good, but what if you want absolute values?

 

[USER]

Given the cache of engineering experience within the ASR membership I would imagine someone could easily design and breadboard an opamp-based gain stage that has the needed specs.

JP and I both use this: https://ka-electronics.com/shop/index.php?route=product/product&product_id=98
Note that it is a balanced preamp, so it requires possible turntable modification to set-up correctly.

I then use the instrument-grade E1DA Cosmos as the ADC.

 

[ray_parkhurst]

Hmm, requires TT mod? $200? That is probably a non-starter for these experiments.

 

[JP]

It can run SE.

 

[ray_parkhurst]

It may be that the recorder @BMRR(VE) intends to use can do this work. I'll need to check with him first. If so, then we may do the first recordings with a wideband approach. If not, then this will need to wait until the next experiment, and we'll need to solicit funds or donations for the added equipment. Even if we do a wideband approach, we might end up doing an RIAA approach in parallel and compare the results. I think that might be good both for the experimental validation as well for the community.