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Preamp with LS Jfets
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Old 26th March 2018, 05:43 PM   #1
Nelson Pass is offline Nelson Pass  United States
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Preamp with LS Jfets
Default Preamp with LS Jfets

This was presented at BAF four years ago, and I thought I had written
it up, but if I did I can't find it.

Here's the graphics of a nice line level gain stage which has no loop feedback.

Attached Images
File Type: jpg 10 LSK SCH.jpg (271.6 KB, 1659 views)
File Type: gif 11 lsk damp.gif (6.7 KB, 1632 views)
File Type: gif 12 lsk dfrq.gif (7.8 KB, 1521 views)
File Type: gif 13 LSK WAV.gif (3.9 KB, 1497 views)
File Type: gif 14 lsk resp.gif (9.1 KB, 1478 views)

Last edited by 6L6; 31st March 2018 at 04:36 PM.
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Old 26th March 2018, 05:46 PM   #2
Nelson Pass is offline Nelson Pass  United States
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Oh yeah, I mis-titled the thread. No balanced here.
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Old 26th March 2018, 06:05 PM   #3
Gyuri is offline Gyuri  Hungary
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Baad Papa, you mislead me.
You know, I need balanced.
But if we are here, can it be used parallel, one for + and one for - side?
Thus if we have four of them, we have a nice balanced stereo set.
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Old 26th March 2018, 06:08 PM   #4
WalterW is offline WalterW  Netherlands
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Preamp with LS Jfets
What will be the V+ and V- ?
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Old 26th March 2018, 06:21 PM   #5
osscar is offline osscar  Latvia
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Thank you for sharing - it looks like it could be good opamp alternative for whammy headphone amp !
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Old 26th March 2018, 06:24 PM   #6
MASantos is offline MASantos  Portugal
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Quote:
Originally Posted by osscar View Post
Thank you for sharing - it looks like it could be good opamp alternative for whammy headphone amp !
And easily built on a small perfboard with dip8 adapter.
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Old 26th March 2018, 07:15 PM   #7
Soundhappy is offline Soundhappy  France
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LS jfet line stage by Mr. Pass at BAF video

PSU V(-)(+)= 45V
LS jfet's Idss range = 15 mA
output gain = 15 dB
output impedance = 1K5

All this specyfications numbers are right ?
Please correct if not Kind regards
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Old 26th March 2018, 07:36 PM   #8
Nelson Pass is offline Nelson Pass  United States
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That sounds right.
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Old 26th March 2018, 07:58 PM   #9
wdecho is offline wdecho  United States
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Built it a few years back. My favorite linestage I have built and tried over many others. I do not understand why someone has not designed a board for this schematic. Not hard to build on a perfboard but probably more interest if a board were available. Not the prettiest wiring but hey it works and it is quiet even with linear supply. Better sounding to me than the couple of BA-3 pre builds I have done. You may notice I placed some caps on the output just to prevent any DC in case some was there. I bought the 2 set of 8 j-fets from the store in C grade and got close enough matching for the pairs needed.
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File Type: jpg P1030781.JPG (540.5 KB, 745 views)

Last edited by wdecho; 26th March 2018 at 08:07 PM.
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Old 26th March 2018, 08:11 PM   #10
juma is offline juma  Serbia
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Quote:
Originally Posted by Nelson Pass View Post
Oh yeah, I mis-titled the thread. No balanced here.
Quote:
Originally Posted by Gyuri View Post
Baad Papa, you mislead me.
You know, I need balanced. ....
Actually, there is a balanced output version of this circuit, as per Chris Hornbeck's proposal from 2011 (post #148) :
phase splitter issue

Click the image to open in full size.
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Last edited by juma; 26th March 2018 at 08:17 PM.
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