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Old 18th October 2012, 09:59 PM   #341
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Quote:
Originally Posted by Joachim Gerhard View Post
I can not tell if it has potential.
To make it clear YOU do not want to parallel, so the Interfet is the only choice.
If you accept paralleling forget the Interfet. 10x BF862 is not the same but to a first order approximation extremely similar.
Yes, that paralleling solves the gain and the noise problem-
Whatever works out us good enough. I will try to parallel 10 BFs and give it a try and if works out obviously the interfet part will be the part I am looking for.

Overall we are talking about 40 jfets paralleled for balance right? If they are biased at 6mA each 240mA for front stage seems crazy though.
Here is the other big pro of the if part which gets up to that gm with only 10mA am I wrong?
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Last edited by Stefanoo; 18th October 2012 at 10:11 PM.
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Old 18th October 2012, 10:02 PM   #342
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MiiBs one shot will need 20 Bfs. Make that 16 because when you parallel more then 8 per side nothing happens any more. Yes, run the input stage hot, there is no other way.
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Old 18th October 2012, 10:12 PM   #343
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This guy is actually not my friend but his noise calculations are hard to criticize.
Here you can learn everything you have to know about designing for low noise at low impedances with BJT and JFet.Low Noise Designs
When you have swallowed that pill we can proceed. Noise, hum and distortion is simply not allowed when you design for SOTA.
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Old 18th October 2012, 10:32 PM   #344
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Quote:
Originally Posted by Joachim Gerhard View Post
This guy is actually not my friend but his noise calculations are hard to criticize.
Here you can learn everything you have to know about designing for low noise at low impedances with BJT and JFet.Low Noise Designs
When you have swallowed that pill we can proceed. Noise, hum and distortion is simply not allowed when you design for SOTA.
I had already read that and talked a bit to the guy too.
However I will re-read it again.
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Old 19th October 2012, 10:55 AM   #345
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The good thing about BF862 is that they need less current to sound good than the SK170's so you can run them at may 3 ma each... so in total you get around 50 mA for a LTP input.
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Old 19th October 2012, 02:51 PM   #346
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Originally Posted by MiiB View Post
The good thing about BF862 is that they need less current to sound good than the SK170's so you can run them at may 3 ma each... so in total you get around 50 mA for a LTP input.
that is pretty good.

Do you guys think I can make a SE version with BFs to compare against Paradise?
Making the balance version and then changing cables and topology running the preamp balance wouldn't give me a straight idea whether this topology has potential to sound better or not.
I know that with balance I gain 6dB gain.

What do you guys think? Would this be a logical approach?
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Old 19th October 2012, 03:13 PM   #347
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Yes, that would be a start.
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Old 19th October 2012, 03:15 PM   #348
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Quote:
Originally Posted by Joachim Gerhard View Post
Yes, that would be a start.
good. But will I get enough gain out of it paralleling let's say 8 BFs in Single End configuration?
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Old 19th October 2012, 03:35 PM   #349
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here is the simulation.
I can't get anymore than this gain out of it and apparently I need 100mA at the input.
Beside switchin on the simulation from K170 to BF862 didn't bring any gain up.

Please help with the simulation (MiiB?!?) -models attached here-
Attached Images
File Type: jpg simulation.JPG (131.5 KB, 89 views)
Attached Files
File Type: asc Temp-TRANS-Z SIMPLIFIED.asc (15.0 KB, 3 views)
File Type: txt Library.txt (3.2 KB, 2 views)
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Old 19th October 2012, 04:23 PM   #350
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So you get 55dB gain unbalanced, that will give you 61dB balnced, i think that is fine.
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