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Old 8th May 2016, 06:11 PM   #1
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Question Jensen JT-44K-DX MC Step-up loading doubt

How to load Jensen JT-44K-DX MC Step-up (the manual says 6K81 + 200p), without loading the cartridge sees 470 Ohms,if I want to change for example the cartridge sees 100 ohms I have to tuning loading the secondaries with 12.700 ohms = 12K7. The question is what loading have I to use? I guess the Jensen manual is to damp the self resonance of the cartrige and cartrdige sees 25 ohms? Or I have to no follows the Jesen manual and loading only with the 12K7 resistor in place of 6K81 + 200p?


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Old 8th May 2016, 06:27 PM   #2
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Who knows how to calculate the series RC termination across the secondary for a desired cartrige loading?

I read in Vinyl Asylum "Jensen says that for a 40-ohm cartridge the termination should be 6.04k-ohms in series with 130-pF" http://www.audioasylum.com/audio/vin...69/695238.html
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Old 8th May 2016, 07:19 PM   #3
dimitri is offline dimitri  United States
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There is no simple way to calculate the series RC damping networks for
microphone input transformers. Please refer to adjustment procedure from Jensen
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Old 9th May 2016, 08:01 PM   #4
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Nobody more?
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Old 11th May 2016, 01:14 AM   #5
TomWh is offline TomWh  United States
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I am assuming that from the 470 ohm load to the cart it is a 1 to 10 step up into a 47k phono stage resistor. I have played a lot with loading on step up transformers but not with a cap to make it a official zobel network.

Right now I am running a resistor in front and a 1 mil in the rear. Got the idea from another forum. Now if you can not change the one on the phono pre this will not work.

If you are going to parallel the rear just try as many combos to see what sounds the best for your cart. My demon 103r is at 68 ohms. Denon 103 at 150 ohms. Grado low output at 470 ohms.

There are people who like front load others rear and a few who like front/rear. Not many who thought the zobel did much good sound wise. So back to the reality of your system and cart, try different values and listen.

Enjoy the ride Tom
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Old 11th May 2016, 12:55 PM   #6
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Thanks Tom.
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Old 11th May 2016, 01:24 PM   #7
SY is offline SY  United States
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It should be done experimentally. I describe the procedure in the His Master's Noise article. I believe it's also described on Sowter's page about their 8055 transformer.
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Old 11th May 2016, 01:32 PM   #8
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Thank you SY.

How to calculate the input impedance of a phono preamp?

I guess the values for Zobel and load for Sowter 8055 1:10 will be the same for other 1:10 MC step-up?

What happens if the cartridge have a output resistance of more than 10 ohms?

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Old 11th May 2016, 02:14 PM   #9
SY is offline SY  United States
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Quote:
Originally Posted by merlin el mago View Post

I guess the values for Zobel and load for Sowter 8055 1:10 will be the same for other 1:10 MC step-up?

What happens if the cartridge have a output resistance of more than 10 ohms?
In order: no, and change the source impedance of the test signal to match the cartridge.
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Old 11th May 2016, 02:27 PM   #10
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So I have to load the primary with the DC resistance of the cart and feed a 1kHz square wave signal of 0.4mV if it's the same DC output of my cart. Manufaturer data-sheet says "Proper loading provided by standard 47 kΩ phono input" so I have to put the Zobel between the tx and a 47K load resistor and see what happens with the square wave, the next question is how to know if I have to increase or decrease resistor & capacitor value to tame the ringing?
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