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Old 22nd April 2009, 08:56 PM   #1
svokke is offline svokke  Belgium
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Default B1 JFET alternatives list

The B1 thread is already bigger than 1500 posts. In this big pile of information I'm not able to find which JFET's can be used instead of the standard 2SK170/LSK170/2SK370 types.
Purpose of this thread is to make a list with suitable replacement JFET's for use in the B1 buffer. Any information on the performance of the replacement devices compared with the standard ones is welcome.
Some possible alternatives:
J309
J310
2sk117
2N5459
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Old 22nd April 2009, 10:15 PM   #2
Magura is offline Magura  Denmark
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2SK369


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Old 22nd April 2009, 10:16 PM   #3
juma is offline juma  Germany
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BF861B suits perfectly (transconductance & Idss):
http://search.digikey.com/scripts/Dk...=568-1967-1-ND

Datasheet:
http://pdf1.alldatasheet.com/datashe...IPS/BF861.html
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Old 22nd April 2009, 10:34 PM   #4
mlloyd1 is offline mlloyd1  United States
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these two links have some other recommendations used in similar circuits:

this tech note talks in detail about the buffer circuit and proposes some different jfets.

the schematic here on page 22 features a similar circuit and uses yet another model jfet. (last time i bought some of these, they were pretty cheap).

it's a simple enough circuit that almost anything could be used, even the lowly 2N5457. I've seen the 2N5486 used over the years in various op amp test circuits (many years ago, you used to find useful things in data sheets besides data - imagine that ). you'll need to play with the biasing because fet characteristics are all over the map.

have fun ...
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Old 23rd April 2009, 01:21 AM   #5
EUVL is offline EUVL  Europe
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2SK369 is a VERY good suggestion.

BF861 has a bit too much noise. I would suggest using BF862 instead. You can read about measurements of the BF862 by Scott Wurcer from the Blowtorch thread.

Of course 2SK370, 2SK117 are all good alternatives.

You can also read my reasoning here :

B1-Turbo on a Chip

I personally would not waste time with the rest. They either have too much noise or too low Yfs. And 2SK170 is still sooooo easy to get....

Just my 2 cents.


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Old 23rd April 2009, 10:22 AM   #6
juma is offline juma  Germany
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Quote:
Originally posted by EUVL
.....BF861 has a bit too much noise. I would suggest using BF862 instead....
Patrick, if you look at at the BF861's noise figure (in attachment) you'll see that it's good even for phono stage and we are talking line-level buffer here


BF862 is a great part, but it cannot be used in B1 without some adaptations in schematic. In B1 JFETs are running at Idss and dissipation will be a problem - up to Id of 10mA will be OK
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Old 23rd April 2009, 04:35 PM   #7
EUVL is offline EUVL  Europe
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I said all I would want to say in the other thread, including how to use the BF862 for B1.

I actually have a whole bunch of BF861Bs sitting for months on my workbench. You are welcome to buy them off me. All measured for Idss already.


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Old 23rd April 2009, 05:51 PM   #8
juma is offline juma  Germany
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Quote:
Originally posted by EUVL
I said all I would want to say in the other thread, including how to use the BF862 for B1.
I actually have a whole bunch of BF861Bs sitting for months on my workbench. You are welcome to buy them off me. All measured for Idss already.
Patrick
Thanks for the offer, but I'm already waiting for my new batch of 862's. I agree with you about these JFETs, it's just that some people are not comfortable with idea of changing Nelson's design - BF861 might be better for them if k170 is unobtainable...
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Old 23rd April 2009, 06:51 PM   #9
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Quote:
Originally posted by juma
I agree with you about these JFETs, it's just that some people are not comfortable with idea of changing Nelson's design.
That's unfortunate. The simplicity of this stuff begs for
experimentation.

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Old 23rd April 2009, 07:30 PM   #10
EUVL is offline EUVL  Europe
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Yeh. They wouldn't even try my SMD B1-Turbo !!

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