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.

Matching JFETs, JFET behavior
Matching JFETs, JFET behavior
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
Thread Tools Search this Thread
Old 9th February 2018, 02:35 PM   #1
woofertester is offline woofertester  United States
diyAudio Member
Join Date: Jun 2011
Default Matching JFETs, JFET behavior

I bought some 2SK170s and some 2SJ74s to build F4 boards from the DIY Audio Store. The boards are on the way.

Never used JFETs before so it is all new to me.

I want to match N-P pairs for this F4 build and for future builds.

My assumption is that, for testing/matching, I want to choose a Vds close to the usage case and also that gm around zero Vgs should be close for the matched pair. Is this correct?

Now a behavior question. I am using 20V Vds for the matching exercise. I set the gate to zero volts and measure drain current. The current starts a 10.18ma and eventually ends at 10.355 mA after a long wait (minutes). The same long settling happens at -0.1V Vgs and +0.1V Vgs.

It seems that the JFET takes a while to come to equilibrium. Is this due to self-heating?
  Reply With Quote
Old 9th February 2018, 03:35 PM   #2
WalterW is online now WalterW  Netherlands
diyAudio Member
Join Date: Oct 2012
Location: Utrecht
Matching JFETs, JFET behavior
Yep, the Toshibas tend to climb in Idss when heating up. Even when you breathe around them they change in Idss. Or open a window.
20Vds x 10.18mA = around 200mW, that's half the maximum dissipation.
Don't go to far with + voltages at the gates for 2sk170. (and - voltages for 2SJ74)
Pass F5, F5Tv3, ACA, Aleph J, DDDAC1794, DCB1, BA3-preamp, VFET CSX1, Pass F6, Pass M2-HPA, VFET-X balanced, Pass J2
  Reply With Quote
Old 9th February 2018, 04:14 PM   #3
woofertester is offline woofertester  United States
diyAudio Member
Join Date: Jun 2011
These will be used in an F4. So the gates will both swing +/-24v, yes?
  Reply With Quote
Old 10th February 2018, 01:05 AM   #4
aspringv is offline aspringv  Australia
diyAudio Member
Join Date: Sep 2010
Location: Perth, Western Australia
Matching JFETs, JFET behavior
Edit : disregard. I'm a dummy.

Last edited by aspringv; 10th February 2018 at 01:08 AM.
  Reply With Quote


Matching JFETs, JFET behaviorHide 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
Questions regarding the matching of jfets Delete Parts 0 23rd July 2016 11:49 PM
JFETs replacing and matching questions Joshua_G Analogue Source 86 9th October 2014 04:35 PM
Matching Jfets NickC Solid State 13 23rd December 2013 11:18 PM
matching jfets analog_guy Analogue Source 29 9th August 2010 05:59 PM
Matching Jfets Sunsun22 Solid State 3 20th January 2010 02:08 PM

New To Site? Need Help?

All times are GMT. The time now is 01:04 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio