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Cartridge dynamic behaviour
Cartridge dynamic behaviour
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Old 16th March 2018, 09:57 AM   #21
gpapag is offline gpapag  Greece
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Cartridge dynamic behaviour
Yes, right. Lucky has provided some measurements here mechanical resonance in MMs

I have used a signal generator in series with a cartridge to plot the frequency response and impedance vs freq of the electro-magnetic part in the past to good effect.
Doing it with varying signal level should be a good way to test for the dynamic behavior of a cartridge.

I am also thinking of in-vivo testing.
Playing a 33.3RPM test track at various speeds (16, 33.3, 45, 78 RPM) with a electro-dynamic cartridge (velocity sensitive) will vary the output (together with the pitch) but I am not certain of how much.

George
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Old 16th March 2018, 01:49 PM   #22
luckythedog is offline luckythedog  United Kingdom
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Going through the archive, here's Lloyd Dixon's Texas Instruments treatment of eddy current losses, which I think is usefully balanced as to not being too math heavy, and is well presented. Overall it highlights some unexpected features of coils as relevant to eddy current loss.

www.ti.com/lit/ml/slup197/slup197.pdf

LD

Last edited by luckythedog; 16th March 2018 at 01:58 PM.
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Old 16th March 2018, 05:53 PM   #23
jaddie is offline jaddie
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Originally Posted by luckythedog View Post
That's untrue. a) Different test records have different test levels, especially pink/white noise tracks.
Perhaps, but what you need is a single test record, all recorded with the same lathe, no RIAA EQ applied, and at different levels. Otherwise you have included WAY to many variables in this, like different RIAA record EQ nets, each unconfirmed, different vinyls, etc... This in no way verifies the purported dynamic FR variance.
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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.
Yeah, but where's all of that analysis spread over a wide dynamic range? A 2-port network does not specifically imply dynamic nonlinearities.
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On the contrary, it's been an historical assumption that f response is independent of level.
Beg to differ, but you're welcome to verify that.
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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.
Well, I've had extreme curiosity for decades. I'm not one to join dots on completely different pages, though.

The original version of your post mentioned that the use of test records was unnecessary, that we could "any broad spectrum programme content"...with fades.
I'm very glad you decided to change that, because that absolutely does not work. I hope we're not going to be dealing with other assumptions like that one.

Last edited by jaddie; 16th March 2018 at 06:01 PM.
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Old 16th March 2018, 06:06 PM   #24
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Originally Posted by gpapag View Post
Yes, right. Lucky has provided some measurements here mechanical resonance in MMs
That's the first bit of interesting information thus far. Thanks!
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Old 16th March 2018, 07:44 PM   #25
luckythedog is offline luckythedog  United Kingdom
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Perhaps, but what you need is a single test record, all recorded with the same lathe, no RIAA EQ applied, and at different levels.
Sure. But the lack of such of a test record is a double edge sword. By your reasoning, neither can it ever have been shown that f response is independent of level............

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Otherwise you have included WAY to many variables in this, like different RIAA record EQ nets, each unconfirmed, different vinyls, etc...
This wasn't an intentional experiment originally. It arose accidentally from examination of many and various cartridges using several test records, and obtaining repeatable but cartridge specific variances. Then spotting a correlation in variance with test level. That's still a valid enough method though. But messy even to explain let alone present. It's just a marker for something that is unexpected and probably real, so as stimulate further investigation and explanation for the curious mind.

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...we could "any broad spectrum programme content"...with fades.
That would be messy, 2nd rate. Better to get smart and inventive with 'in-vivo' tests, targeting non-ideals using the test records we have.

LD
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Old 16th March 2018, 10:56 PM   #26
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Sure. But the lack of such of a test record is a double edge sword. By your reasoning, neither can it ever have been shown that f response is independent of level............
Not true at all, but you don't currently have the right test record. There's nothing double-edged about not having the right tool.
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This wasn't an intentional experiment originally. It arose accidentally from examination of many and various cartridges using several test records, and obtaining repeatable but cartridge specific variances.
There there should exist a data set that shows the results.
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Then spotting a correlation in variance with test level.
Given the above data set, anyone should be able to extract that correlation. If we had the data.
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That's still a valid enough method though. But messy even to explain let alone present.
I don't find that messy in any aspect. I find it thus far devoid of data.
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It's just a marker for something that is unexpected and probably real, so as stimulate further investigation and explanation for the curious mind.
A trend in data should not be difficult to see and correlate. Determining cause is another matter.
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That would be messy, 2nd rate. Better to get smart and inventive with 'in-vivo' tests, targeting non-ideals using the test records we have.

LD
It's actually worse than messy, it's impossible. You'd have a test signal that changes spectrally vs time vs level. In other words, 3 variables are built into the test signal. That disqualifies it as a test signal when trying to isolate a single external variable. Just bad science. I've used real-time spectrum analysis on program material for many decades, I know very well what those limitations are. Just to extract an repeatable spectrum you need to integrate many spectral "samples" over a long period of time. If the overall level is changing, the integration becomes dominated by high level samples, and progressively less by low level samples. It's an invalid technique, and I'm glad we can dismiss it.
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Old 17th March 2018, 12:16 AM   #27
luckythedog is offline luckythedog  United Kingdom
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There there should exist a data set that shows the results.
Of course.

But let's examine your claim that f response is independent of level. Where is your data set for that ? It's just assumption.........

LD
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Old 17th March 2018, 12:21 AM   #28
gpapag is offline gpapag  Greece
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Cartridge dynamic behaviour
First try of MM cartridge impedance plots with varying excitation level.
I used the impedance jig that I use for measuring speaker units, only standard resistor is 500 Ohms.
M-Audio USB Audiophile soundcard. Rout=150 Ohm, Rin=10kOhm
REW software, data exported to Excel (jaddie, I can't make REW Impedance axis show above 1kOhm)
Tomorrow I will redo the test with shorter wires. I think that phase plot hints to high capacitance of the wiring.
The mVrms signal across the cartridge coil was spot measured at 100Hz

George
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Old 17th March 2018, 12:35 AM   #29
luckythedog is offline luckythedog  United Kingdom
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Originally Posted by gpapag View Post
Tomorrow I will redo the test with shorter wires. I think that phase plot hints to high capacitance of the wiring.
The mVrms signal across the cartridge coil was spot measured at 100Hz

George
Thanks George.

Is it possible to use signal levels roughly similar to those occurring in playback, so 0dB=5mV, and a range from +10dB to -50dB or as small as is practicable to measure?

LD
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Old 17th March 2018, 12:43 AM   #30
jaddie is offline jaddie
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Originally Posted by luckythedog View Post
Of course.

But let's examine your claim that f response is independent of level. Where is your data set for that ? It's just assumption.........

LD
Read my posts again carefully. I'm not making that claim. I'm asking you to prove yours. There is a difference.
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