Matching Jfets - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

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 2nd December 2003, 01:45 PM   #1
diyAudio Member
 
Join Date: Dec 2001
Location: Earth
Default Matching Jfets

I need a circuit that can help me match Jfets to a specific current range of Idss 4-6ma and another circuit than can match them for gate source voltage. Can anyone point out a circuit that can do so. Thanks
  Reply With Quote
Old 2nd December 2003, 01:53 PM   #2
Netlist is offline Netlist  Belgium
diyAudio Moderator Emeritus
 
Netlist's Avatar
 
Join Date: Jan 2003
http://www.passdiy.com has a brilliant tool for that job.

/Hugo
  Reply With Quote
Old 2nd December 2003, 10:52 PM   #3
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
I hope that Nelson has shown how to do this, BUT it is fairly easy with just a multimeter. You just short the gate to the source and add a 9V battery from the drain to the source. This gives you Idss. But how to measure? Put a 10 ohm resistor between the drain and the battery and measure across it. 0.1V=10ma and so forth. Matching Vbe is much more difficult.
  Reply With Quote
Old 4th December 2003, 02:23 PM   #4
peufeu is offline peufeu  France
diyAudio Member
 
Join Date: Mar 2001
Location: Lyon, France
Default DMM

I use a multimeter set on 200 mA caliber and short grid to source...

I then take a sheet of paper, mark a scale from (for instance) 15 to 40 mA, and drop the transistors on the scale after measuring them. That's an easy way to group them without headaches...
  Reply With Quote
Old 4th December 2003, 08:44 PM   #5
diyAudio Member
 
johnferrier's Avatar
 
Join Date: Sep 2003
Location: WA
Default Re: DMM

Quote:
Originally posted by peufeu
I then take a sheet of paper, mark a scale from (for instance) 15 to 40 mA, and drop the transistors...
Can you recommend good JFETs in the 15-40mA range? How many would it take to find 4 that match at around 20mA? Is 10% considered an adequate match? And how much better would 2% matches be???

What I have in mind is matching 4 JFETs for the outputs to a headphone amplifier (for 300 ohm Sennheisers). I'm thinking about 2sk170, but don't know if I would need to buy 20, 50 or a 100 (to find enough that "match").

Sorry for a barrage of questions (I don't know if someone is reading that knows such things "like the back of their hand"). TIA.


JF
  Reply With Quote
Old 5th December 2003, 06:41 AM   #6
peufeu is offline peufeu  France
diyAudio Member
 
Join Date: Mar 2001
Location: Lyon, France
Default JFETs

I have only used JFETs to cascode bipolars so can't comment directly on their sound qualities.

I have used J309 in my DAC and that works well (and is cheap, too).

I think J309 would fit your bill, maybe. Look at the IDss values...
  Reply With Quote
Old 5th December 2003, 10:58 PM   #7
diyAudio Member
 
johnferrier's Avatar
 
Join Date: Sep 2003
Location: WA
Default Re: JFETs

Quote:
Originally posted by peufeu
I have only used JFETs to cascode bipolars so can't comment directly on their sound qualities.

I have used J309 in my DAC and that works well (and is cheap, too).

I think J309 would fit your bill, maybe. Look at the IDss values...

: )


JF
  Reply With Quote
Old 6th December 2003, 01:38 AM   #8
Banned
 
Join Date: Feb 2002
Location: As far from the NOSsers as possible
Default 2SK170s........

If you really need that much current, assuming that you have the BL group, you can put 4 in parallel to get that amount of current. Maybe with 3, but 4 to be certain.

Jocko
  Reply With Quote
Old 6th December 2003, 01:44 AM   #9
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Hi,

Quote:
you can put 4 in parallel to get that amount of current. Maybe with 3, but 4 to be certain.
Current sharing resistors not included? Or are they?

Cheers,
__________________
Frank
  Reply With Quote
Old 6th December 2003, 02:28 AM   #10
diyAudio Member
 
johnferrier's Avatar
 
Join Date: Sep 2003
Location: WA
What comes closest to what I have in mind is Borbely's "Super Buffer" which is figure 8 at the following link:

http://www.borbelyaudio.com/borb502.pdf

I'm thinking of parallelling 4, 5, 6...or whatever of the jsk170/jsk74 to get 100mA. It seems that violet parts would help me get there at a lower part count (and are just a little more cost). Maybe you're suggesting 5 ohm series resistors to allow for differences between JFETs. Figure 9 shows a MOSFET version (with higher current output), but Borbely suggests that an all JFET amplifier would be the best.

My question is how closely matched (10, 5, 2%) do the k170/j74 pairs need to be?


JF
  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
SiC JFETS revintage Pass Labs 15 27th August 2009 02:43 PM
JFETs for 5ma CCS? PhopsonNY Parts 7 24th December 2008 03:55 AM
jfets for preamp kzeprf22 Solid State 14 21st November 2008 02:35 PM
F3 jfets needed coils Pass Labs 4 5th October 2007 08:23 PM
Matched JFETs suzyj Solid State 8 22nd August 2007 02:10 AM


New To Site? Need Help?

All times are GMT. The time now is 05:27 PM.


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