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Old 29th November 2012, 08:51 PM   #7771
RCruz is offline RCruz  Switzerland
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Old 29th November 2012, 09:20 PM   #7772
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As high as possible. The current sources are ok, i think more then 20MOhm.
The problem is the parallel impedance of the input stage.
For the RIAA the values of the Pardise could be taken. One problem to solve the output impedance is to load the input stage with a single ended Paradise mirror.
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Old 29th November 2012, 11:00 PM   #7773
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Quote:
Originally Posted by RCruz View Post
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Remenber the computer in kubrik film 2001 ?

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every time I see Papa avatar
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Old 29th November 2012, 11:08 PM   #7774
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Oh, I thought the avatar meant toilet seat still occupied and Pap's not coming out just yet, so don't wait up.
(stupid me, what was I thinking)
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Old 30th November 2012, 12:18 AM   #7775
MiiB is offline MiiB  Denmark
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Or One could run a simulation to see... what the output impedance is... bet it's swamped with all kinds of capacitive parasitics.
The CCS could also be made with Depletion mosfets...
I think some research has been made on the BF862 jfet regarding performance and current. I think I remember something about that it in contradiction to the SK170 does not need high(ish) current to sound good..2-3 mA should be sufficient. (pls correct me if I remember wrong)
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Old 30th November 2012, 01:09 AM   #7776
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Yes, it runs on low current well but the original idea was to have as high transconductance in the input as possible. That requires high idle.
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Old 30th November 2012, 01:11 AM   #7777
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Old 30th November 2012, 01:15 AM   #7778
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here is transconductance visa idle of BF862
i think 12.5mA is optimal hence the 10 Ohm degeneration
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Old 30th November 2012, 01:17 AM   #7779
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It is nearly double then on 3mA ( 25mS visa 40mS ), sure the 2SK170 degenerates more drastic.
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Old 30th November 2012, 08:37 AM   #7780
MiiB is offline MiiB  Denmark
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youre right, then the Css must deliver 50 mA.. putting some pressure on the cascode transistors.. dissipating 25mW/V... Think it may be advisable to find a TO126 or a TO220 transitor for the cascoding..KSA3503/KSC1381 could be a possible choice.
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