Help Matching JFET's - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

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 29th January 2011, 11:46 PM   #1
diyAudio Member
 
Join Date: Aug 2009
Location: Sacramento
Question Help Matching JFET's

Hello,
I am looking for help selecting a 0 to 19.99 ma digital panel meter for matching JFET Idss.
I have a meter that read to tenths of a ma I want one that reads to 0.00, Hundredths of a milliamp.
I realize that it would cost less to by matched items. As it is I bought a gob of 2SK170’s and a tenth of a ma is as close as it gets with the meter on hand.
DT
All just for fun!
  Reply With Quote
Old 31st January 2011, 04:47 AM   #2
diyAudio Member
 
Join Date: Aug 2009
Location: Sacramento
Hello,
This
DCA-20PC-3-DC4-RL-C Murata Power Solutions Digital Panel Meters
Is the solution I picked, not cheap! It is no wonder matched JFETS go for a large mark up.
DT
All just for fun!
  Reply With Quote
Old 31st January 2011, 04:53 AM   #3
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
I built my FET matching jig so that a standard DVM could plug in for both voltage and current measurements (one each). Since it's the relative measurement that really counts in matching, a fairly humble DVM can serve as long as all the FETs are matched in the same session with the same meter. It's worked for me for a number of years, even in fiddly applications like jfet SRPP preamps.
  Reply With Quote
Old 31st January 2011, 05:39 AM   #4
diyAudio Member
 
Join Date: Aug 2009
Location: Sacramento
Hello,
This may be in the range of too many toys.
I wanted that extra digit. I am not finished yet. The jig is getting a LM317 or 1085 voltage regulator set to the standard 10 volts DC. Using a 9 volt battery and watching the Idss drift as the voltage drooped under load drove me nuts.
This is turning into a project I guess.
Wrenchone I have followed your JFET threads. It looks like you have it working well.
DT
All just for fun!
  Reply With Quote
Old 31st January 2011, 05:19 PM   #5
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
I have a setting on my jig for IDSS, but what I generally test for is Vgs using fixed 1, 2, 5, and 10ma current sources and sinks. - just a bunch of separate "ring of 2" sources.
  Reply With Quote
Old 1st February 2011, 02:50 PM   #6
diyAudio Member
 
Join Date: Aug 2009
Location: Sacramento
Quote:
Originally Posted by wrenchone View Post
I built my FET matching jig so that a standard DVM could plug in for both voltage and current measurements (one each). Since it's the relative measurement that really counts in matching, a fairly humble DVM can serve as long as all the FETs are matched in the same session with the same meter. It's worked for me for a number of years, even in fiddly applications like jfet SRPP preamps.
Hello,
I am new to JFETs. As far as matching Idss it seemed like the place to start. Wrenchone you remind me that there are also other parameters that come into play. The test jig is being built into a surplus instrument chassis with ample room to add other features.
If you will tell us more about your preference to measure voltage relative to current as the preferred matching method.
DT
All just for fun!
  Reply With Quote
Old 1st February 2011, 05:36 PM   #7
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
Look at post #49 in my JFET SRPP thread for a circuit for testing Vgs at a given drain current.
  Reply With Quote
Old 2nd February 2011, 05:13 AM   #8
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
I've sorted jfets using either IDSS or VGS at specified drain current. If using low power sources like 9V batteries, the IDSS method gets a little awkward at higher currents, and you may risk crisping an especially lively fet. This is especially true for low RDS/high IDSS devices like the PN4391. The Vgs/IDS method is easier on the fets (and the batteries), and gives you guidance as to how to set appropriate source resistors for a desired drain current.
  Reply With Quote
Old 2nd February 2011, 06:48 AM   #9
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

could look like this:
Click the image to open in full size.

jauu
Calvin

Last edited by Calvin; 2nd February 2011 at 06:55 AM.
  Reply With Quote
Old 2nd February 2011, 07:48 AM   #10
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
Could look different, too. Maybe a board for sale to follow, who knows?
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Hi-Voltage JFET's Workhorse Solid State 56 16th August 2012 05:46 PM
Hi-Voltage JFET's mojoat Swap Meet 1 28th December 2007 10:01 AM


New To Site? Need Help?

All times are GMT. The time now is 09:28 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2