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Cartridge dynamic behaviour
Cartridge dynamic behaviour
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Old 14th March 2018, 11:08 PM   #11
billshurv is offline billshurv  United Kingdom
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Cartridge dynamic behaviour
If you mean posts by LD, he will have supporting data. I am trying to find some of the stuff that survived the purge on this to see if there is anything useful. Just because a graph hasn't been posted doesn't mean one doesn't exist. If you followed the links in my long post you will see plenty of graphs. They just don't need repeating here.

But this will be a (possibly long) process of discovery.
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Old 15th March 2018, 02:23 AM   #12
jaddie is offline jaddie
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Originally Posted by billshurv View Post
If you mean posts by LD, he will have supporting data. I am trying to find some of the stuff that survived the purge on this to see if there is anything useful. Just because a graph hasn't been posted doesn't mean one doesn't exist. If you followed the links in my long post you will see plenty of graphs. They just don't need repeating here.

But this will be a (possibly long) process of discovery.
You linked to a thread with hundreds of posts. I started with a few, it was all about resonances. How about at least linking to something about this dynamic behavior, or the graphs you speak of? I'm not up for reading that thread. It seems to be about stiff that is already known, and being re-discovered.
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Old 15th March 2018, 01:36 PM   #13
esl 63 is online now esl 63
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The stylus is sampling the groove....
Look at this video and rethink how cartridge work...

YouTube
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Old 15th March 2018, 01:41 PM   #14
luckythedog is offline luckythedog  United Kingdom
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Originally Posted by billshurv View Post
I don't see why I should have to follow things like 47k loading for a cartridge. I can do what I want if the end result is a more accurate reproduction.
Indeed, opportunity certainly is out there.

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Originally Posted by billshurv View Post
Moving on: Up for discussion is the attached snip from an ortofon brochure for the 520 series from around 40 years ago. This was the first appearance of the split pin generator that Ortofon still use to this day. The claim is eddy current reduction. There is a comparion between solid and split pins. Ortofon use B&K plotters set at 50dB scale for all their other FR measurements, so safe to assume 1dB per division. This does show the classic mid-range dip that some cartridges have. Why this is interesting is that you can still get new cartridges with both pole pin constructions in the OM and superOM ranges and the stylii are interchangeable allowing some testing to be done. And testing is needed as we immediately run into the first problem which was discussed at length in the mechanical resonance thread* here mechanical resonance in MMs, which came to a grinding halt mainly due to my inability to complete a test board. However George did build a unit and came up with some interesting data using a Shure M97.
Well, thanks to you, the advanced position on having multiple transimpedance loaded preamps available should make this thread very interesting I think.

TI loading eliminates the LCR resonance, and so makes for far easier analysis of f response and other methods when looking at contributions from mechanics and magnetics.

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If you look here mechanical resonance in MMs, there is the transmission line model LD has worked on that does show the possibility of this sort of level of enhancement. I still don't like it as that infers an exceedingly undamped setup.
Transverse mechanical TL models are probably best for cantilevers, IMO. As it stands the model is quite basic and just shows the correct form surprisingly easily. Bending losses can be slew rate and displacement sensitive, BTW.

In developing the model sufficiently to include real behaviour of bending losses, we'll pretty much end up understanding what really goes on with cantilevers and settle a few myths along the way I suspect.

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So we need some measurements that try to isolate cartridge response from cantilever.
The way I approached this in the past was to examine coil losses as a 2-port network looking into the pins of the coil. i.e to investigate non-ideal inductive behaviour as an electrical coil, and see how that varied with level. Especially for small signals, there's not much existing material on it. I got as far as verifying significant changes to electrical impedance with level for small signals.

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Originally Posted by billshurv;5371289[URL="http://www.diyaudio.com/forums/analogue-source/303389-mechanical-resonance-mms-post5008802.html"
mechanical resonance in MMs[/URL] shows a measurement of the ortofon solid pin generator using a transimpedance circuit LD designed and build and I have a variant waiting for me to get off the internet and build. With a loading scheme that puts cartridge electrical resonance out the picture you can see that you get a flat response within a gnatfart across the audio band**. There is a rising response indicating something, possibly mechanical, but it's not anywhere near that you would expect cw vR or ortofon.
Yes, I assume the rising response is due to top mechanical resonance. And the Aurak TI preamp used was as per the schematic, no fudges.

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Overall I am not sure the generally accepted cartridge electrical model is correct! But I have probably missed something as usual . If we are to explore losses in the generator, we need to make sure we have a half decent generator model to start with?
I agree, the accepted model isn't complete, and fixing that will probably be a good place to start.


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**LD will need to explain if he had any additional corrections in place to get this response.
No additional corrections, and level was 1.2cm/s lateral at 1kHz with some break at 10kHz, spot frequency sine tones.

LD
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Old 15th March 2018, 02:48 PM   #15
billshurv is offline billshurv  United Kingdom
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Cartridge dynamic behaviour
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Originally Posted by jaddie View Post
You linked to a thread with hundreds of posts. I started with a few, it was all about resonances. How about at least linking to something about this dynamic behavior, or the graphs you speak of? I'm not up for reading that thread. It seems to be about stiff that is already known, and being re-discovered.
I linked to specific posts that contained useful information. Yes, stuff is being rediscovered, but if you look at the number of shure technical papers, and AES papers where concepts were accepted that don't stand scrutiny.

In this case I was making the point that, if you need 10-13dB of resonant boost at 20kHz from the stylus assembly, a transimpedance loaded cartridge would be 10-13dB up at 20kHz. It's not, its 1-2dB up. A comparative measurement on a Shure M97xe showed similar. Therefore something is fishy with the simple LRC model of a cartridge and the preamp loading. Something worth of investigation as part of working out how we proceed to find out more about dynamic effects.

Once the penicillin takes effect I should have the few hours needed to get my transamp working then we will have 3 that members here have to do testing on. What I am missing is a test record with different levels on, but still looking around for something suitable.
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Old 15th March 2018, 03:17 PM   #16
luckythedog is offline luckythedog  United Kingdom
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What I am missing is a test record with different levels on, but still looking around for something suitable.
Indeed. I'm not aware of one, but do have an independent look. Persuading the test record thread to re-up the suggested level sweep tests might be the best prospect?

LD
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Old 15th March 2018, 03:26 PM   #17
billshurv is offline billshurv  United Kingdom
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Cartridge dynamic behaviour
I am working on that. They are actually on the current track list.
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Old 15th March 2018, 06:44 PM   #18
jaddie is offline jaddie
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...And there's the real elephant in the room. No actual tests have ever been made of this so-called dynamic response issue because the only available test records have only sweeps at 0db re: 3.54cm Per Second or -14dB with RIAA record EQ.

I wonder when they'll discover the problem with cutting multiple level sweeps on a test record. Probably will have to talk to an actual lathe operator for that one. Hopefully someone figures out this can't be done with RIAA eq on all the sweeps if you really want to cover the full DR, or want accurate FR.
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Old 15th March 2018, 07:41 PM   #19
luckythedog is offline luckythedog  United Kingdom
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Originally Posted by jaddie View Post
No actual tests have ever been made of this so-called dynamic response issue
That's untrue. a) Different test records have different test levels, especially pink/white noise tracks. This correlates well with observed deviation in response for some cartridges, as though deviation and level are correlated variables b) loss mechanisms have been characterised in cartridge coils as a 2-port network.

On the contrary, it's been an historical assumption that f response is independent of level. Unless one has curiosity enough about loose ends, join the dots or think about theoretical non-ideals, apparently it's gone unchallenged. But an assumption it is, and not a safe one. For good reasons.

Nature is full of such non-linearities and loss mechanisms. Ears. Microphones (they grow on Decca trees )

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Hopefully someone figures out this can't be done with RIAA eq on all the sweeps if you really want to cover the full DR, or want accurate FR.
Obviously. So turn RIAA off, limit the f range to levels supported. Not all level contours can be full spectrum in vinyl playback.

LD

Last edited by luckythedog; 15th March 2018 at 07:44 PM.
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Old 15th March 2018, 11:52 PM   #20
billshurv is offline billshurv  United Kingdom
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Cartridge dynamic behaviour
I missed the link to George's measurements on the lowly Shure M97. They can be found here mechanical resonance in MMs . (at least assuming my ability to x-ref works). Now there comparing traditional 47k loading with trans loading you can see approximately 4dB difference at the top end. Now the shure is fairly massive assembly so one might expect they Engineered in some 'help' from the resonances, but a far cry from the circa 13dB you might expect from some sources.

So for me a good working assumption is that there is 2-4dB peaking at 20kHz that may be caused by the mechanical system, ready to be shot down as more data appears.

I should note, for experimental purposes and, if you can take a small noise hit you can take out the HF pole in RIAA and load the cartridge down to give that roll off for free.

I've been doing a little bit of messing around with numbers to see if I can find a starting mechanical model and right now all I can work out is that most people have a LOT more capacitance than they think. Work in progress....
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