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Phono cartridge self resonance
Phono cartridge self resonance
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Old 19th January 2019, 04:28 PM   #11
luckythedog is offline luckythedog  United Kingdom
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Originally Posted by scott wurcer View Post
Thinking around a late coffee, isn't there only one component here a big distributed R/L/C.
Life itself is a transmission line, one comes to realise. Yes, if its a single layer sequentially wound coil. After that it gets tricky because multilayer coils have cross coupled C between turns on different layers. There's not much literature on it, AFAIK.

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Old 19th January 2019, 05:54 PM   #12
scott wurcer is offline scott wurcer  United States
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Originally Posted by billshurv View Post
The main measurements from George are here Cartridge dynamic behaviour . Too many toddlers around for me to deeply re-read at the moment
Some of the coil measurement basics FYI.

https://link.springer.com/content/pd...9075-2%2F1.pdf

Thankfully the toddlers belong to my children now. I might try some measurements (a few more bins to unpack) . Lucky, I assume most carts are wound with something like #50 wire any idea on turns/layers (just enough to make a guess if I find any good references). I have a sawed open Grado somewhere but they are the exception.

EDIT - Most references, obviously, seem to focus on high Q RF applications.
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Last edited by scott wurcer; 19th January 2019 at 06:06 PM.
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Old 19th January 2019, 09:31 PM   #13
billshurv is offline billshurv  United Kingdom
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Phono cartridge self resonance
I have one sacrificed cartridge I could try and count and a couple more I could give up for the cause. How many samples are we likely to need to conclude if self resonace ever ocurs in the audio band?
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Old 20th January 2019, 12:34 AM   #14
PRR is offline PRR  United States
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Originally Posted by luckythedog View Post
So why doesn't MM coil parasitic C show up in after dinner conversations, audible performance, and measurements affecting f response etc etc ?...
It is lumped-in with the capacitance of the wiring and the tube grid capacitance.

Most of this C being unavoidable (until headshell preamps), the industry convention is to apply 47K and adjust capacitance to get resonance at "the top of the audio band".

This allows the cart designer to trim the L-R-C bump to compensate the top octave of the pickup.

While interwinding capacitance is a thing, on a simple winding like this it just builds-up and can be sufficiently approximated as a single C.
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Old 20th January 2019, 12:48 AM   #15
billshurv is offline billshurv  United Kingdom
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Phono cartridge self resonance
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Originally Posted by PRR View Post

This allows the cart designer to trim the L-R-C bump to compensate the top octave of the pickup.
.

We tried to find evidence of this. There are several seemingly compelling models that suggest this bump is needed, but if you then measure using a preamp that is free from Capacitive loading issues you don't get a top octave roll off. At least on anything made since about 1972.



But some of the data still doesn't fully make sense....
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Old 21st January 2019, 05:37 PM   #16
billshurv is offline billshurv  United Kingdom
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Phono cartridge self resonance
back on coil self resonance not sure if this is of use Moving-Magnet Head Amp - without RIAA appears to show a distinct notch at 50kHz.
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Old 25th January 2019, 09:43 AM   #17
gpapag is offline gpapag  Greece
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Phono cartridge self resonance
LD and Bill’s call for electrical self resonance

50 Ohm signal generator in series with a Shure M97xE to single-ended Aurak RIAA preamplifier. M97 self resonance shows up a bit above 40kHz
mechanical resonance in MMs
mechanical resonance in MMs
mechanical resonance in MMs
Input resistance of Aurak is here
mechanical resonance in MMs

Manual spot frequency measurement
mechanical resonance in MMs

Test record playback
mechanical resonance in MMs

George
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Old 25th January 2019, 11:03 PM   #18
luckythedog is offline luckythedog  United Kingdom
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Originally Posted by gpapag View Post
Guys we are off track...….
I thought that, when I realised the negative input impedance stage drives the non-inverting input of the op-amp. Then the simulator confirms, curiously, that the stage overall is inverting...…..(!?!) Phew so that's fair game at least

Thanks for the links to your coil self-resonance measurements, George. That's how I recall it. I still think that's odd though, perhaps some winding method. This would equally apply to audio transformers wouldn't it, which is a better charted water?

LD
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Old 26th January 2019, 09:04 AM   #19
luckythedog is offline luckythedog  United Kingdom
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A quick look at self-resonance of good quality mic transformers suggests self-resonance at c 250kHz. I think such transformers are prob magnetically similar enough to cartridges to consider it not to be an issue, and George's tests confirm this.

Some reference to self C not depending proportionally on number of turns, diminishing increases with each extra turn.

I don't understand it, but happily accept it. Besides, it's good news for low Z input impedance preamps.

LD
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Old 26th January 2019, 02:11 PM   #20
scott wurcer is offline scott wurcer  United States
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Originally Posted by luckythedog View Post
Some reference to self C not depending proportionally on number of turns, diminishing increases with each extra turn.
I originally though of building a distributed self resonance model via the L of one layer and the C to the next but that soon makes no sense since the C's are in series and as L grows the C goes down. I suspect the entire structure along with the mutual coupling is involved.
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