Interest in matched JFETs? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

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 1st October 2015, 07:38 AM   #1
FrankD is offline FrankD  United States
diyAudio Member
 
Join Date: Sep 2015
Location: New York
Default Interest in matched JFETs?

Greetings everyone!

I designed a rather extensive JFET tester for my own personal use (After testing a few hundred JFETs to make a single Forssell JFET OpAmp the manual way, I decided I was never doing that again) and was trying to gauge if there was any interest in the DIYAudio community for sets of JFETs. I've been around for years under a different user name.

I'd be willing to spearhead the purchase of MANY JFETs if there were some PNs that were in heavy demand. My tester uses a 24-bit Sigma-Delta ADC with TL072 opamp buffers on each JFET at the measurement test point and an Atmel AVR to spin data out to a PC which records it in a SQL database and makes matching pretty simple.. and as soon as my Alpha-quality boards get in (I was using an Arduino Due with the onboard ADC and relay boards with some really simple single layer PCBs before), I'll be able to test 48+ at a time.

My simpler tester was actually nicer in some regards, I could just flip the socketed TL072 around to test P-channel JFETs and change the input polarity to the board. In the interim I have separate boards for N/P devices. It's been a fun learning experience since the most I've done before was chip amps, and I've had a few failed experiments along the way!

JFET Tester Part 3

JFET Tester Part 4

This isn't an advertisement, just wanting to see if I can do something for the community. I'd also be willing to test quantities of JFETs for DIYAudio members. I have a small stock (300) of J203s that I was going to test and play with, mainly for my JFET Guitar experiments..

Eventually I'd like to build something like The Beast With (well over) a Thousand JFETs as the power stage in a guitar amplifier with some nifty JFET stuff before the power stage.

Feel free to ask questions, recommend JFETs to test (yeah, I know.. 2SK170 and 2SJ74.... would be nice if I could get them in quantity and know they weren't fakes!) for my own use or for your use, or to comment on how bad I am at making PCBs and drilling holes! I'd prefer you ask in the post, but I'm more than happy to answer PMs.
  Reply With Quote
Old 1st October 2015, 02:34 PM   #2
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
What does your jFET tester measure?
What parameters are you "matching"?
__________________
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote
Old 2nd October 2015, 03:20 AM   #3
FrankD is offline FrankD  United States
diyAudio Member
 
Join Date: Sep 2015
Location: New York
Just your standard Idss and Vpp readings at multiple voltages. If there are other parameters I should test I'd love to hear about it! I'm new to the whole discrete thing and how transistors work is still kind of like voodoo to me.
  Reply With Quote
Old 2nd October 2015, 03:32 AM   #4
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Maybe you'd want to read Erno Borbely's articles from audioXpress which are archived on Linearsystems website: http://www.linearsystems.com/assets/...%20Bordely.pdf
__________________
Why, silly hare, are you fleeing from the fierce jaws of the lion now grown tame?
  Reply With Quote
Old 2nd October 2015, 03:41 AM   #5
FrankD is offline FrankD  United States
diyAudio Member
 
Join Date: Sep 2015
Location: New York
jackinnj, do you mean to look for more parameters to measure or to understand JFETs? I have read that document, or at least pieces of it.. I have it bookmarked
  Reply With Quote
Old 2nd October 2015, 05:06 AM   #6
diyAudio Member
 
dchisholm's Avatar
 
Join Date: Mar 2011
Location: St Louis, Mo
The BF862 shows up in a lot of audio projects, even though it's not specifically an "audio" transistor. The CPH3910 from On Semiconductor is a roughly comparable device on paper though I don't recall ever seeing one in a project. I might fantasize about being able to purchase pairs matched for Idss and Vp - or even narrow bands of Idss - and guaranteed low-frequency noise specs, but in reality I doubt I'd actually buy more than a couple dozen in a lifetime.

Dale
  Reply With Quote
Old 2nd October 2015, 08:28 AM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by FrankD View Post
Just your standard Idss and Vpp readings at multiple voltages. If there are other parameters I should test I'd love to hear about it! I'm new to the whole discrete thing and how transistors work is still kind of like voodoo to me.
matching of multiple Id (they can't all be Idss) and multiple Vp (how do you get multiple Vp from one device?) would be good if your system manages temperature well.

I consider that an LTP style jig with thermal coupling is the only final arbiter for checking a matched pair, when Tj control is not well managed in single device parameter measurement.
__________________
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote
Old 2nd October 2015, 08:50 AM   #8
FrankD is offline FrankD  United States
diyAudio Member
 
Join Date: Sep 2015
Location: New York
I've noticed the parameters vary with supply voltage with the test circuit I'm using, which
is a slight variation of the one on the Fetzer Valve page:

Click the image to open in full size.

Only the current variation has the SPDT switch (which was a relay in previous iterations) replaced with a MOSFET, and the reading is buffered by a JFET input op-amp which is then attenuated with a voltage divider and the ADC taking its readings there (necessary for some of the higher power devices which exceed the 5v logic level + AREF of the uC/ADC). But being a 24 bit ADC, I feel the accuracy will still be high for lower power devices as well.

Temperature will be managed by running air through the case at a controlled inlet temperature, though I could pair up some thermal sensors with the devices and machine sleeves/use a spring/something to couple them tightly mechanically.. that would require another ADC on the board though.

Devices will be 'warmed up' for at least a minute before taking a reading. It would be easy to record the ambient box temperature though, since I do have some extra ADC pins on the uC, but the thermal dissipation curve should be the same for devices of the same type, no? ie Two 2SK170 with 15mA Idss and 1.105v Vp should both have the same Tj with the airflow since ambient is constant.
  Reply With Quote
Old 2nd October 2015, 08:52 AM   #9
FrankD is offline FrankD  United States
diyAudio Member
 
Join Date: Sep 2015
Location: New York
What do you mean they can't all be Idss? Perhaps I'm confused somehow? But I should be reading Vp/Idss. Each DUT is completely isolated from one another, I can just do 16 per board once I get my OSHpark boards in.. and I have enough components to populate 3 N and P channel boards.
  Reply With Quote
Old 2nd October 2015, 09:16 AM   #10
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Idss is when Vce = specified value and when Vgs =zero volts and when Tj=25C
That can ONLY happen at one measurement,
Any other current is Id.
__________________
regards Andrew T.
Sent from my desktop computer using a keyboard
  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
New list for pair matched transistors/jfets/fets siliconray Siliconray Online Electronics Store 2 6th November 2013 12:02 AM
Matched JFETs for DIYers NYCOne Swap Meet 4 13th May 2011 10:29 AM
WTB matched jfets for F5 ! komigenie Swap Meet 4 16th March 2011 01:54 AM
Audio Electronic Components JFETS Matched Transistors Capacitors Etc haltechrx7 Swap Meet 8 7th January 2011 09:01 PM
Matched JFETs suzyj Solid State 8 22nd August 2007 03:10 AM


New To Site? Need Help?

All times are GMT. The time now is 03:31 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright 1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki