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Cartridge dynamic behaviour
Cartridge dynamic behaviour
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Old 19th March 2019, 01:32 AM   #871
davidsrsb is offline davidsrsb  Malaysia
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Achieving that low a tolerance in inductance is a hard task given variation in permeability, wire diameter.
Output voltage level also factors in the magnet strength.
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Old 19th March 2019, 09:30 AM   #872
billshurv is offline billshurv  United Kingdom
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Cartridge dynamic behaviour
It is a hard task, but when you have been making effectively the same generator for 40 years one might think that they had the process down to a fine art. If of course they were bothered!


I suspect their might be some selection going on so the more expensive models get the better matching. Certainly AT/Signet did that in the 70s.



Anyway back on the accuracy deviation from this. Hans came up with a very different answer to me and still trying to work out what I have done wrong. I looked at it from a reference point of 1kHz as all RIAA accuracy is normally done and from that starting point to my eyes everything is fine from 500Hz upwards as the pole and zero are all handled. The problem comes with the correction for initial roll off from the trans loading. So for example the correction starts at 318Hz but the actual cart rolloff doesn't start until 350Hz. To me this area is the only error and will be of the order of a dB of so (need to calculate this as lost my notes on that). Now I have biquads to burn on miniDSP so a simple shelf to correct this would work for me (and we are well into the modal range in my room).



What have I missed?
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Old 19th March 2019, 11:35 AM   #873
davidsrsb is offline davidsrsb  Malaysia
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Left-right matching will naturally be good as they share the same core material and the coils are going to be wound from the same wire spool. You can probably make a lot of cartridges from one spool
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Old 19th March 2019, 12:02 PM   #874
billshurv is offline billshurv  United Kingdom
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Cartridge dynamic behaviour
Ortofons don't share cores (although the 4 cores will more than likely be off the same batch). But agree on the spool.
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Old 19th March 2019, 06:46 PM   #875
Hans Polak is offline Hans Polak  Netherlands
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Today I have played the Pink Noise track on the Adjust+ record at 33 1/3, 45 and 60.75rpm.
Two things were very different to the CH Precision record:

1) Each step upwards in speed resulted in shifting the spectrum by 1.3dB upwards, whereas with the CH Precision record all 3 spectra where on top of each other.
But this time it finally proves after all that a speed change by 1.35x results in 2.6dB level increase.
Why this did not happen on the CH record remains a mystery.
2) Spectra where shifting horizontally a factor 1.35 each time, but did not show the strange behaviour from the CH Precision record where at 45rpm FR was within +/-0.5dB up to 30kHz, but at 33 1/3rpm 20kHz was 3dB down.

This all shows that the world of recorded Pink noise has it's own laws and dynamics.
Depending on factors not at all clear to me, every record behaves differently.
Only the CH record is within +/-0.5dB from 2kHz to 30kHz when played at 45rpm and should at this speed be an ideal medium to further investigate MM Carts.


Hans
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Old 19th March 2019, 10:49 PM   #876
luckythedog is offline luckythedog  United Kingdom
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Quote:
Originally Posted by Hans Polak View Post
This all shows that the world of recorded Pink noise has it's own laws and dynamics.
Exactly. Unfortunately, real programme material more closely resembles pink noise than f sweeps.....

Quote:
Originally Posted by Hans Polak View Post
Depending on factors not at all clear to me, every record behaves differently.
Exactly.

Quote:
Originally Posted by Hans Polak View Post
Only the CH record is within +/-0.5dB from 2kHz to 30kHz when played at 45rpm and should at this speed be an ideal medium to further investigate MM Carts.
Perhaps, but maybe it is tuned or a happy coincidence to give that result, and who is to say what is a real and true response? This is tricky. I thought to use a calibrated mechanical jig to move the stylus as a reference - but how to calibrate any such jig is the problem...….? Interferometry perhaps.

LD
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Old 19th March 2019, 11:13 PM   #877
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by luckythedog View Post
but how to calibrate any such jig is the problem....? Interferometry perhaps.

LD
A high quality piezo-accelerometer should not need further calibration the trick would be to find one that does 20kHz. Another thing, I have not read the B&K article in detail but how do you excite the cartridge in other than a purely vertical direction?
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Old 20th March 2019, 04:08 AM   #878
1audio is offline 1audio  United States
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Originally Posted by scott wurcer View Post
A high quality piezo-accelerometer should not need further calibration the trick would be to find one that does 20kHz. Another thing, I have not read the B&K article in detail but how do you excite the cartridge in other than a purely vertical direction?
The B&K accelerometer is in a little stand on some foam going horizontally. I think you can tilt the stand but I'm not sure that would get to 45 degrees and still hold the cartridge. As I remember there were several of those exact accelerometers on eBay a short while ago. Still some: Bruel & Kjaer 8307 Piezoelectric charge shock accelerometer /DS 0041 | eBay
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Old 20th March 2019, 10:54 AM   #879
luckythedog is offline luckythedog  United Kingdom
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IIRC the B&K article used a piezo accelerometer as a motor, but it required extensive calibration that personally I remain unconvinced about, and a thumping in-band resonance.

I had considered a mechanical cam based vibrating platform, or voice coil actuated platform. But still calibration and proof of no self-resonance remains tricky.

Still, it would be fun to have a go.....

LD
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Old 20th March 2019, 11:57 AM   #880
scott wurcer is offline scott wurcer  United States
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Originally Posted by luckythedog View Post
IIRC the B&K article used a piezo accelerometer as a motor, but it required extensive calibration that personally I remain unconvinced about, and a thumping in-band resonance.
I was thinking of using it as a sensor with something else as a driver but still there is the resonance issue. There are 3 axis MEMS accelerometers but I'm not sure any are over a few kHz.
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