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Cartridge dynamic behaviour
Cartridge dynamic behaviour
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Old Yesterday, 06:35 PM   #1281
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by scott wurcer View Post
In other words if you drive the circuit with a voltage in series with R you get a large voltage gain, but obviously no power gain.
LD I hope you're with me here, it's an impedance transformation so the voltage goes up and the current goes down (or visa-versa) just like with a transformer so the power/energy is constant. The relationship between R and Q squared in the L/C circuit is analogous to R and N squared in a transformer.
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Old Yesterday, 09:11 PM   #1282
Hans Polak is offline Hans Polak  Netherlands
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I finalized my search for finding replacements circuits for all 5 Carts that Bill made available.
There are great differences, like between the inductance of the Ortofon 40 versus the Denon DL-107.
Nevertheless most carts seem to perform quite well in a classical voltage amp setup.
All Ortofons needed a somewhat larger cap of resp. 250pF for the Ortofon Super OM10 and the Ortofon 40, and 350pF for the Ortofon S-120 to prevent an early roll off at high end
The Denon DL-107 and the AT 150MLX where fine with 47k//150pF.

For the Virtual ground topology, the Ortofon 40 and S-120 did not respond that well, despite meticulous tuning to cancel the created pole and needed an extra 11usec pole to keep HF under control.
The other 3 Carts didnít need such correction.
All 5 Carts showed an extended BW in the Virtual Ground topology, just as expected.

My test gear was suited for testing above 2mV on the Cart. To go any lower will need the use of bandpass filters to lower the scopes noise of 100uV.
Although these filters are available, it will make the testing process to take considerable more time and for the moment I donít see a real need to go much lower.

One thing has to be kept in mind. I measured the replacement circuits as if a constant voltage is generated by the motor when playing at CV.
This will most likely not be the case, so when knowing the recorded FR from a well known test record, like the CH Precision record up to 30kHz or the Ortofon record up to 50kHz, both played at 45rpm,will enable to finding the transfer function from CV to motor voltage.
This would definitely help to get more insight in the Carts functioning.
I leave this recording job for these 5 Carts to someone else since my system is not optimised for MM Carts, but will be happy to help in finding the missing transfer function.


To keep things together, the final results for all 5 Carts together are attached.

Hans
Attached Images
File Type: png AT150MLX-2.png (42.4 KB, 56 views)
File Type: png Deno DL-107.png (42.3 KB, 59 views)
File Type: png Ortofon 40.png (47.3 KB, 60 views)
File Type: png Ortofon S-120.png (48.6 KB, 59 views)
File Type: png Ortofon Super OM 10.png (42.9 KB, 59 views)
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Old Yesterday, 10:42 PM   #1283
billshurv is offline billshurv  United Kingdom
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Cartridge dynamic behaviour
Hans, that's really interesting, particularly as it shows a real difference between the solid and split pin ortofon generators. The DL-107 is a very pleasant suprise as shows that their patented design does work as described and that they knew their onions before I was born!



I'll get something set up to measure FR ASAP.



My oddball lo-Z MMs are still in transit from Russia. When they arrive they are having a detour to Belgium for a friend to try them. If you have the time to run those as well let me know.
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Old Today, 05:22 AM   #1284
luckythedog is offline luckythedog  United Kingdom
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Quote:
Originally Posted by scott wurcer View Post
LD I hope you're with me here, it's an impedance transformation so the voltage goes up and the current goes down (or visa-versa) just like with a transformer so the power/energy is constant. The relationship between R and Q squared in the L/C circuit is analogous to R and N squared in a transformer.
Yes, thank you Scott - I get it now. Noise power remains unaltered: it is as you say a source impedance transformation.

Then noise voltage would follow Re versus f, and not be white.

A way to validate the cart's impedance at very low signal levels would be to observe voltage noise spectrum - not easy though?

LD
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Old Today, 05:45 AM   #1285
Hans Polak is offline Hans Polak  Netherlands
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Originally Posted by luckythedog View Post
Yes, thank you Scott - I get it now. Noise power remains unaltered: it is as you say a source impedance transformation.

Then noise voltage would follow Re versus f, and not be white.

A way to validate the cart's impedance at very low signal levels would be to observe voltage noise spectrum - not easy though?

LD
Are you still interested in very low signal levels ?
Then please select one of the 5 Cart’s that I tested and I will process that guy.
Noise BW now is 100MHz, so I can go a factor 100 down in noise when restricting to 10kHz.
Now that I have the wideband data I only have to compare.

Hans

Last edited by Hans Polak; Today at 05:59 AM.
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Old Today, 11:09 AM   #1286
Hans Polak is offline Hans Polak  Netherlands
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LD,

I took one sample with the Ortofon Super OM 10, the one that was rapidly increasing its inductance at voltages above 30mV.
Now just as a simple test at 1kHz, with restricted noise BW, where in the bode diagram with the 4k7 series resistor gain was -6.0dB with a phase of 42.5 degrees, I went from 11.4mV to 24.4uv on the cart, a full 53 dB down with no measurable change in gain and phase. Since these gain and phase figures are 1:1 related to the inductance, this tells that Inductance doesn't change over this range.
Let me just know if you want me to do any other test now that I still have everything set up and working properly.


Hans
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Old Today, 12:17 PM   #1287
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by luckythedog View Post

A way to validate the cart's impedance at very low signal levels would be to observe voltage noise spectrum - not easy though?

LD
I did plot 25yr. ago to show why you don't want to use a super low noise bi-polar with a MM cart. I just used a fixed gain of 200 pre-amp in front of an HP dynamic signal analyzer and the noise was easy to resolve. IIRC it was an AT cart with an 800 OHM DC resistance. The difference between the AD745 and LT1028 was large, but with the 5534 not as much but the FET still won.
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Old Today, 02:11 PM   #1288
Hans Polak is offline Hans Polak  Netherlands
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I even could go a bit lower to 10.7uV on the OM 10 Cart, 60 dB below 11.4mV that was mentioned before as an upper limit.
See screen capture below, not the nicest possible waveforms, bit still 6dB apart.
Channel A is the reference input with 21.2uV and channel B with 10.7uV the node between Cart and 4k7.
Measured RMS voltages are displayed in the bottom line.
I used the scope's internal 50* amp, so noise is still there, but now with BW limited to 3kHz.

Hans
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File Type: png Picoscope1.png (40.0 KB, 3 views)
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