Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Pass Labs This forum is dedicated to Pass Labs discussion.

JFET matching
JFET matching
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 31st December 2005, 08:40 PM   #1
Nelson Pass is offline Nelson Pass  United States
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
JFET matching
Default JFET matching

Since people are going ahead on purchasing the Lovoltech
power JFETs, I thought I would share some of my matching
data.

It's quite simple, as seen from the circuit. A measurement of
the Vgs under identical conditions is adequate for most
applications. The value is useful for creating differential pairs,
and in cascoded single-ended applications becomes valuable
when selecting a Source resistor to ground.

In the case of selecting a Source-to-ground resistor, the value
of the resistance can be used to set up the optimal load line
for the lowest distortion.
Attached Images
File Type: jpg vgs test.jpg (39.7 KB, 1822 views)
  Reply With Quote
Old 31st December 2005, 08:41 PM   #2
Nelson Pass is offline Nelson Pass  United States
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
JFET matching
Here's a distribution of values of the population of a couple
of tubes:
Attached Images
File Type: jpg jfet dist.jpg (33.1 KB, 1652 views)
  Reply With Quote
Old 31st December 2005, 08:53 PM   #3
Nelson Pass is offline Nelson Pass  United States
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
JFET matching
Depending on all the other usual factors, optimizing the
Source resistance in a cascoded single-ended system can
improve the performance quite a bit. Your results will vary
somewhat, and so for a given circuit design, it is necessary
to test to find the optimal values, but here is an example
of a distortion curve in an arbitrary system where the cascode
has a grounded Gate. One curve shows the untrimmed value
of Source resistance, and the other has been adjusted slightly.
Attached Images
File Type: gif jfetm03.gif (10.3 KB, 1492 views)
  Reply With Quote
Old 31st December 2005, 08:57 PM   #4
Nelson Pass is offline Nelson Pass  United States
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
JFET matching
For this same circuit, here is a curve of optimal resistance
values for a range of Vgs values. Again, this is simply an
example of a single design, and these values should not be
applied in general. For a given design, there will likely be a curve
which resembles this in principle which will obtained by actual
testing.
Attached Images
File Type: jpg optimal resistance.jpg (36.4 KB, 1460 views)
  Reply With Quote
Old 31st December 2005, 08:58 PM   #5
Nelson Pass is offline Nelson Pass  United States
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
JFET matching
Happy New Year.

  Reply With Quote
Old 31st December 2005, 10:26 PM   #6
Zen Mod is offline Zen Mod  Serbia
Official Court Jester
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
JFET matching
Quote:
Originally posted by Nelson Pass
Happy New Year.

same to you and your folks



and many more-spent in good health and fun


hehe
same wishes to any DIYer around
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 1st January 2006, 03:53 PM   #7
Alain Dupont is offline Alain Dupont  France
diyAudio Member
 
Alain Dupont's Avatar
 
Join Date: Sep 2003
Location: Paris - France
Nelson, and all DIYer's

Happy New Year,

lot's of circuits and thanks so much for your
power JFETs matching advise.

Alain.
  Reply With Quote
Old 2nd January 2006, 01:56 AM   #8
jh6you is offline jh6you
Account Disabled
 
Join Date: Aug 2002
Location: Near to the Pacific Ocean
How much I have learned thru Pass Labs forum . . .
Looking back myself . . .

Happy New Year !!!

  Reply With Quote
Old 2nd January 2006, 03:16 AM   #9
Looneytunes is offline Looneytunes  United States
diyAudio Member
 
Join Date: Oct 2005
Thanks Nelson,
and Happy New Year to you and all.
  Reply With Quote
Old 6th January 2006, 05:30 PM   #10
tmblack is offline tmblack  United Kingdom
diyAudio Member
 
Join Date: Jan 2005
Location: UK
Mr. Pass,

How close do the Jfet's need to be matched as diff pair and as cascode?

Tom
  Reply With Quote

Reply


JFET matchingHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
JFet matching and measured distortion - Part1 h_a Solid State 22 27th March 2009 07:41 PM
JFet matching and measured distortion - Part 2: LTP h_a Solid State 27 27th March 2009 06:40 PM
Ono JFET matching AuroraB Pass Labs 12 26th July 2007 01:20 PM
JFET in-circuit matching Leolabs Solid State 5 9th April 2006 02:44 PM


New To Site? Need Help?

All times are GMT. The time now is 12:26 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki