Preamp with LS Jfets

[Nelson Pass]

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.

 

[Nelson Pass]

Oh yeah, I mis-titled the thread. No balanced here.

 

[Gyuri]

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.

 

[WalterW]

What will be the V+ and V- ?

 

[osscar]

Thank you for sharing - it looks like it could be good opamp alternative for whammy headphone amp !

 

[MASantos]

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.

 

[Soundhappy]

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

 

[Nelson Pass]

That sounds right.

 

[wdecho]

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.

 

[juma]

Oh yeah, I mis-titled the thread. No balanced here.

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

 

[juma]

.... I do not understand why someone has not designed a board for this schematic....

There is one in first post of this thread:
LSK pre - BAF 2013

 

[wdecho]

There is one in first post of this thread:
LSK pre - BAF 2013

I built your version of this design as well and it performs to my ears admirable as well.

 

[Soundhappy]

That sounds right.

Thanks Mr. Pass.
Characteristics looks yummy: low noise and distortion, no feedback loop, excellent frequency wide band response etc.
LS jfet's line stage (PCBs + jfets) if available in DiyAudio Store can be new popular 2018 Top five best seller DIY kit.
Superb line stage alternative choice to match with Aficionados amplifiers

 

[juma]

I built your version of this design as well and it performs to my ears admirable as well.

My version is in post #66.
Post #1 has PCB for MR Pass' version with few values changed for different Idss grade JFETs and some housekeeping parts added.

 

[Adams_Leo]

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.

Dear Mr, Pass,can I use the 2SK389V/2SJ109V to replace the LSK170C/LSK74V?

Thanks
Leo

 

[vdi_nenna]

LSK pre - BAF 2013


LSK Line Stage Original Schematic BAF 2013

 

[Nelson Pass]

can I use the 2SK389V/2SJ109V to replace the LSK170C/LSK74V?

I think so. Worst case would be adjustment of some resistor values.

 

[kasey197]

Is there an article that explains how the preamp works and what the parts do ?
Or perhaps this is an opportunity for a (very) mini tutorial Nelson ?

 

[Zen Mod]

second stage - think of emiter/source cascode

 

[vdi_nenna]

Is there an article that explains how the preamp works and what the parts do ?
Or perhaps this is an opportunity for a (very) mini tutorial Nelson ?

There's a you tube video.

YouTube