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Phono cartridge self resonance
Phono cartridge self resonance
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Old 31st January 2019, 12:33 PM   #41
Bonsai is offline Bonsai  Europe
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ok - good to know
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Old 31st January 2019, 12:57 PM   #42
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by billshurv View Post
does a low-Z load on the cartridge reduce the eddy current effects?
Or does open circuit? I hope I can find my spare carts and do a measurement. The reason I wanted to look at unloaded noise is that the resistive part on MM's is large enough that one should easily be able to resolve the self resonant frequency and Q without any electrical stimulus.
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Old 31st January 2019, 01:33 PM   #43
gpapag is offline gpapag  Greece
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Phono cartridge self resonance
Quote:
Originally Posted by scott wurcer View Post
without any electrical stimulus.
How can this be done?

I found these two by the way.
measuring distributed capacitance
http://www.datatronics.com/pdf/distr...ance_paper.pdf

Fig 17-11 measure with oscilloscope
https://coefs.uncc.edu/mnoras/files/...Chapter_17.pdf


George
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Old 31st January 2019, 02:40 PM   #44
scott wurcer is offline scott wurcer  United States
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Originally Posted by gpapag View Post
How can this be done?

George
Below are two examples, I picked Rod Elliot's split L model just as an example. The first is loaded (100pF||47k) second is unloaded. Both of these are noise only. We can measure the series resistance and the basic low frequency inductance, the noise signature should reflect the loss and, if present, a resonance will give the internal parallel C.

With much difficulty I was able to measure the noise of the DA in a 50pF mica capacitor. Thermo-dynamically all electrical loss mechanisms have an associated noise.

Thanks for the references, they show the possibility of non-minimum phase in these measurements (?).
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Old 31st January 2019, 04:05 PM   #45
gpapag is offline gpapag  Greece
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Phono cartridge self resonance
Scott, nice plots but I haven’t understood your method.
I already knew that you are mastering the noise like no one else here, while I have no clue.
So why do I bother to ask?

Quote:
Thanks for the references, they show the possibility of non-minimum phase in these measurements (?).
Right Scott.
I have seen this in some of loudspeaker impedance measurements, 0 phase and max Z a few Hz apart.
I don’t know why it happens, what is the cause of it.
I want to test it in more details with the carts and inductors.
I prepare the measuring jig for using lower signal levels than the previous runs, hopefully going some 40dB lower.
If I fail, I know whom to ask for help.

George
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Old 31st January 2019, 09:33 PM   #46
billshurv is online now billshurv  United Kingdom
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Phono cartridge self resonance
Been trying to go back a few steps on this and invoke spherical cows. Someone tell me where I'm making a wrong assumption or have physics upside down.


Assuming eddy currents exist and assuming the generator in a MM cart is so inefficient that the wiggling magnet can be ignored.
1. In 47k world eddy currents will be level dependent (possibly testable).
2. For an EC to flow in the iron core, then current must flow in the coil
3. For current to flow there must be a voltage across the windings.

4. In the low-Z world the voltage across the windings is much reduced as the voltage across the cartridge pins tends to zero and only the coil resistance limits this
5. low voltage also means low current in this case (not sure about that)


If all the above is correct then a low Z preamp will show a lot less tendency for a midrange dip


Conversely a higher Z load might increase the dip?


Load the Magnets!!! - [English] has some measurements that might indicate this is the case. Given my lack of trust for pink noise tracks on test records I consider salt is needed, but we might be onto (backonto?) something.



What have I missed?
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Old 31st January 2019, 11:43 PM   #47
davidsrsb is offline davidsrsb  Malaysia
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Quote:
Originally Posted by billshurv View Post
5. low voltage also means low current in this case (not sure about that)....

What have I missed?
I would expect a low impedance load is a maximum current case, not low current.
When the load is 47k or higher, the current flowing is mainly into capacitance

The Datatronics link is interesting, we have several of the problem indicators in a MM
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Old 31st January 2019, 11:52 PM   #48
billshurv is online now billshurv  United Kingdom
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Phono cartridge self resonance
I did too, but if you think that most carts (not the silly ones I have) have a 500Ohm to 1k5 series resistance then you not only have a current limiter, but also your ability to hold the coil near 0V drops as well. If voltage across the coil is zero current is zero in the case of a super low efficiency generator.



I am probably wrong, but it matches some very limited datapoints we have on the midband dip.
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Old 1st February 2019, 12:04 AM   #49
davidsrsb is offline davidsrsb  Malaysia
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Layered coupled windings are still minimum phase.
This is a three layer model and phase is still 90 i most of the band, as you would expect for an inductor
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Old 1st February 2019, 12:11 AM   #50
billshurv is online now billshurv  United Kingdom
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Phono cartridge self resonance
but that doesn't match what has been measured?
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