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Old 26th January 2012, 02:15 PM   #4871
MiiB is offline MiiB  Denmark
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Input capacitance is 4 times that of the input transistor...BC337 is app 5 pF...So a good guess would be 20 pF... looking into low impedance on the source.. roll-of from this is nothing..
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Old 26th January 2012, 02:27 PM   #4872
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Quote:
Originally Posted by Joachim Gerhard View Post
Thanks Michael. http://www.ti.com/lit/an/slyt145/slyt145.pdf
Ricardo, you can grind your mathematical ax on circuit fig.16
It promises accurate RIAA.
I will read it but it seems these use opamps and not an interstage passive filter...
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Old 26th January 2012, 02:28 PM   #4873
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Originally Posted by MiiB View Post
Input capacitance is 4 times that of the input transistor...BC337 is app 5 pF...So a good guess would be 20 pF... looking into low impedance on the source.. roll-of from this is nothing..
Much better than with jfets as I expected
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Old 26th January 2012, 02:29 PM   #4874
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Originally Posted by Joachim Gerhard View Post
I have talked to Jahre and i got some interesting answers. I wanted to know what the smallest case is with 1% precision for RIAA use. It is case 53.
Here are the dimensions :
6,8nF 125V 12,7 x 12,5 x 3,4 10.2mm between wires Case 53.10
13,6nF 125V 12,7 x 12.5 x 5,3 10.2mm between wires Case 53.20
40,6nF 125V 22 x 12.2 x 10,4 20mm between wires Case 53.50

i get a price quote soon

best, joachim
Looking forward for a quote
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Old 26th January 2012, 02:33 PM   #4875
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Well is is actually 8 x , but anyway, BJTs have much less input capacitance ( and hence less open loop distortion ) then J-Fets so this is an advantage of BJTs.
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Old 26th January 2012, 02:41 PM   #4876
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Yes, Ricardo, it is with Opamps but that is not the point. They argue that a conventional filter has mathematical problems to follow the RIAA exactly and this arrangement of 4 Opamps solved that. I find it intellectual interesting, not more.
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Old 26th January 2012, 03:15 PM   #4877
MiiB is offline MiiB  Denmark
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SK170 has input capacitance of 22 pF so this here with a total of 40 pF is roughly the same at one pair of fets, but here we have 4 sets of input devices with much much lower noise and way higher mu..

Last edited by MiiB; 26th January 2012 at 03:18 PM.
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Old 26th January 2012, 04:31 PM   #4878
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The P-channel 2SJ74 has even 105pF. That does really not matter much. An MC cartridge is so low in resistance that the pole created is very high in frequency.
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Old 26th January 2012, 04:35 PM   #4879
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The transistors have arrived Frans, many thanks.
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Old 26th January 2012, 04:54 PM   #4880
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Originally Posted by Joachim Gerhard View Post
We can talk to WIMA. They are in Unna, 80km from my home. I would like FKP2 in 1% with copper or silver wires.
Wima is a good option. I did talk to them some years ago to get special GTO caps for industrial project. They were very helpful and it was not a problem to buy small quantity in OK price.

FKP2 is (so far) copper in RM5 'bauform'. I can get easily 2.5% with no problem but 1% would be much better!!
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