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Old 9th February 2004, 09:55 AM   #41
Aiace is offline Aiace  Italy
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Ok Dimitri I think you right, here is the NF diagram.
but if you look at Hfe diagram you can see that gain at 100uA is half than 1mA. I think S/N at the end is almost the same.
If it's a mistake please tell me.

Thank you
Aiace
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Old 9th February 2004, 02:53 PM   #42
Aiace is offline Aiace  Italy
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Dimitri said than pickup can be modelled by 10-15 kohm. Now I've a question:
A MM pick up like GRADO (http://www.gradolabs.com/product_pages/cartridges.pdf)
has a resistance of 475ohm and an inductance of 45mH. That means 520 ohm @ 1kHz a lot far away from 10-15kohm od Dimitri.

What do you use to model pickup for noise and why?

Thank at all
Aiace
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Old 9th February 2004, 04:52 PM   #43
dimitri is offline dimitri  United States
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>but if you look at Hfe diagram you can see that gain at 100uA is half than 1mA. I think S/N at the end is almost the same.
If it's a mistake please tell me.

Yes, this is a mistake. The differential dc _voltage_ gain of the first long-tailed pair will be (R2+R3)/(2*26mV/Ie+R1). It is nothing to do with hfe - current gain.

>Dimitri said than pickup can be modelled by 10-15 kohm.

Yes, this is for typical MM pickup with a resistance of ~500ohm and an inductance of ~500mH.
I've opened the pdf of Grado, your pickup has ten times lower inductance. If it isn't a mistake I don't understand why Grado has that output . If the inductance of your MM pickup is ~50mH, leave everything untouched. You are lucky!
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Old 9th February 2004, 11:40 PM   #44
Aiace is offline Aiace  Italy
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Yes Dimitri Vu=gmd*Vd where gmd=Ie/(4*26mV)...so as high Ie as high the gain of Vd


Dimitri, I 've looked around for pick up inductance, and I think you give me a clue: I'm going to measure inductance of my pick up but at the moment I can't hear any noise from my phono



Hi
Aiace
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Old 10th February 2004, 07:00 AM   #45
dimitri is offline dimitri  United States
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My dear Aiace
Donít put out your tongue at me . Think before you type .

>Vu=gmd*Vd where gmd=Ie/(4*26mV)...so as high Ie as high the gain of Vd

This is not Vu-voltage, this is Iu-current! Ė and to remain E/2 voltage on collectors while changing Ie you should adjust R2,R3 correspondently

>I can't hear any noise from my phono
Very good

Ciao
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Old 12th February 2004, 09:35 PM   #46
Aiace is offline Aiace  Italy
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Ingenuously I trimmered RV1 before connecting the circuit to the pickup. After several days a suspicion is risen me....
I went to measure the outoput offset and it was 3V !!!!

So I trimmered again RV1 (with the pickup connected) and started to listen at same disks .... Fantastic !! It has been like I cleaned my glasses, or like I cleaned the kitchen windows from the vapor. Finally I obtained the transparency that I love.

Yes, my phono sounds very well, fast and deep low frequencies, very natural in human voices , extremely high dimanic sound, analytic like one x-ray, not noise at all.
I'm very happy of my work 'couse my thoeory of "virtual bilanced" was right

Thank you at all for your advices and patience
Aiace
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Old 5th May 2004, 08:59 AM   #47
thanh is offline thanh  Viet Nam
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why don't you use all fet?
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