Hello,
@Hans Polak thank you very much for the hard work and the willingness to share.
I just spotted the article in audioXpress.
May I ask what is the method to infer the RLC model from the VNA result (for the generator) or from the subtracted FR (for the cantilever assembly)?
Many thanks,
jb
@Hans Polak thank you very much for the hard work and the willingness to share.
I just spotted the article in audioXpress.
May I ask what is the method to infer the RLC model from the VNA result (for the generator) or from the subtracted FR (for the cantilever assembly)?
Many thanks,
jb
Hi JP,
It’s exactly as you mentioned, hard work.
After having measured the generator’s FR, you start with one RC network in LTSpice, which FR turns out to be far off.
So you add a second RC network in between the first R and C which brings you closer the the VNA’s recorded FR, but still not good enough, so a third RC network is inserted and so on until a fourth RC is starting to come close.
Now at HF some fiddling has to be done, for which large R and small C turns out to solve the final puzzle.
Using this generic model for the Next Carts proved to be adequate for all MM carts.
The first Cart took the longest to get the result, but on average I needed at least halve a day per Cart.
Creating the other model for the mechanical part was not that much different.
I subdivided them in the individual parts, indentation, resonance and cut off depending on the speed and position on the disk.
But again, this took on average at least another halve day per Cart.
Hans
It’s exactly as you mentioned, hard work.
After having measured the generator’s FR, you start with one RC network in LTSpice, which FR turns out to be far off.
So you add a second RC network in between the first R and C which brings you closer the the VNA’s recorded FR, but still not good enough, so a third RC network is inserted and so on until a fourth RC is starting to come close.
Now at HF some fiddling has to be done, for which large R and small C turns out to solve the final puzzle.
Using this generic model for the Next Carts proved to be adequate for all MM carts.
The first Cart took the longest to get the result, but on average I needed at least halve a day per Cart.
Creating the other model for the mechanical part was not that much different.
I subdivided them in the individual parts, indentation, resonance and cut off depending on the speed and position on the disk.
But again, this took on average at least another halve day per Cart.
Hans
Hello Hans,
thanks for the explanation.
I checked the datasheet of the AT150MLX and it states Le=360mH@1kHz
that is the same value as the sum in your model 283mH+20mH+25mH+32mW
the resistors in parallel I believe represent the losses due to eddy currents.
All makes sense.
Great work.
jb
thanks for the explanation.
I checked the datasheet of the AT150MLX and it states Le=360mH@1kHz
that is the same value as the sum in your model 283mH+20mH+25mH+32mW
the resistors in parallel I believe represent the losses due to eddy currents.
All makes sense.
Great work.
jb
Hans,
BTW you might want to have a look at
https://preamp.org/static/ltspice-model-from-impedance-measurement-data/index.html
this is really cool: instead of inferring the LRC model, just use real life impedance measurements
directly into LTspice (great tool BTW).
Hope this helps,
jb
BTW you might want to have a look at
https://preamp.org/static/ltspice-model-from-impedance-measurement-data/index.html
this is really cool: instead of inferring the LRC model, just use real life impedance measurements
directly into LTspice (great tool BTW).
Hope this helps,
jb
How does it extrapolate phase? Does it stay passive or can it go beyond +90 degrees or -90 degrees? Does it work in transient analyses?
I ask this because it reminds me of the s parameter models that are often used for RF design. Models of completely passive structures can sometimes oscillate all by themselves when you use the wrong settings for extraction or extrapolation.
Besides, controlled sources normally have no thermal noise, so chances are that the cartridge thermal noise is missing from such a controlled source model.
I ask this because it reminds me of the s parameter models that are often used for RF design. Models of completely passive structures can sometimes oscillate all by themselves when you use the wrong settings for extraction or extrapolation.
Besides, controlled sources normally have no thermal noise, so chances are that the cartridge thermal noise is missing from such a controlled source model.
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billshurv, I believe you supplied all the cartridges for Hans Polak et al
The Technics cartridge in that seminal tome is shown as Technics205-IIX. But the measured & simulated Generator Z is closer to 30R & 39mH which is sorta appropriate for Technics205-IIL, the Low Impedance version of 205-II rather than 500R & 240mH for the 205-IIS (standard) & 205-IIH (high?) versions.
I don't think there were more 'cartridge body' versions for this range of supa cartridges though some re-labelling like 205-IIX
I got the L from the Technics 'intrinsic impedance'. I assumed the Japanese simply measured Z at 1kHz for this.
IMHO, AudioTechnica do the same thing and their numbers sorta tie in with the AT24 you measured/simulated at 240R & 85mH
I would appreciate Hans Polak, Dagfinn Rasmussen & billshurv commenting on this.
The Technics cartridge in that seminal tome is shown as Technics205-IIX. But the measured & simulated Generator Z is closer to 30R & 39mH which is sorta appropriate for Technics205-IIL, the Low Impedance version of 205-II rather than 500R & 240mH for the 205-IIS (standard) & 205-IIH (high?) versions.
I don't think there were more 'cartridge body' versions for this range of supa cartridges though some re-labelling like 205-IIX
I got the L from the Technics 'intrinsic impedance'. I assumed the Japanese simply measured Z at 1kHz for this.
IMHO, AudioTechnica do the same thing and their numbers sorta tie in with the AT24 you measured/simulated at 240R & 85mH
I would appreciate Hans Polak, Dagfinn Rasmussen & billshurv commenting on this.
IIRC there are very few markings on the cartridge body, but the stylus had a sticker on saying 205-IIX so that was used as identification by Hans. It's confusing as there were 2 generators but 3 output levels so the high output was just a bigger magnet on the standard body. I can't fully remember and I'm not sure where that cartridge is now.