I need something to replace this JFET in my microphone preamp (Presonus Eureka). 

The JFET is no longer produced, this is the JFET.

http://laupengineering.com/projects/PreSonus%20Eureka%20Repair/LSM_U441_TO-71.pdf


Whoops

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #1 on: September 27, 2020, 10:15:10 PM »
What is the JFET you're looking for?

RuudNL

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #2 on: September 28, 2020, 03:45:50 AM »
I suppose the Siliconix U441.
There is a solution for every problem!

http://www.vansteenisaudio.nl

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #3 on: September 28, 2020, 04:59:48 PM »
It's the Siliconix U441.  I guess they don't make them anymore, so I need a replacement. 

Whoops

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #4 on: September 28, 2020, 10:05:19 PM »
It's the Siliconix U441.  I guess they don't make them anymore, so I need a replacement.

It's actually 2 matched Jfets in one package. If a replacement doesnt exists, you can match 2 individual FETs with the same characteristics as the ones in the U441 and glue them together





http://musicfromouterspace.com/analogsynth_new/TRANSISTORMATCHER/TRANSISTORMATCHER.html

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #5 on: September 29, 2020, 08:02:50 PM »
I would rather not, if I can find a dual N channel Jfet to replace it, that would be ideal.  anyone? 

rackmonkey

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #6 on: September 30, 2020, 02:13:57 AM »
Linear Integrated Systems is your friend. The U441 is equivalent to the 2N5912, which - like most through hole JFETs - is no longer manufactured by anyone. Except Linear Integrated Systems. If you’re willing/able to work with surface mount, you can get the SST441. However, the LS5912 comes in a TO-71 package. The latter costs a little over $7 at Trendsetter Electronics: https://www.trendsetter.com/ls5912-to-71-6l.html

They also carry the SST441, but you have to call for pricing.

Good luck
Whether you think you can or you think you can't, you're probably right.

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #7 on: September 30, 2020, 01:41:23 PM »
Thank you rack!  When looking for equivalent JFETs...what parameters should I be looking for to match my replacement? 


rackmonkey

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #8 on: September 30, 2020, 04:00:06 PM »
Thank you rack!  When looking for equivalent JFETs...what parameters should I be looking for to match my replacement?

For most signal-path audio applications, Idss, Vgs(off), noise, and yfs will be the parameters of greatest interest. Provided of course that max ratings aren’t exceeded.

2N5912 is the Siliconix recommended sub for the 441. But like most subs, it’s not an exact equivalent performance wise. Primarily, it’s noisier and has higher transconductance, so yfs will have a steeper slope. You may or may not notice much difference in your application. Hard to know without a schematic. But if the JFET pair is on the input, the noise figure will make a difference. That might lead you to the SMD 441 part, which has its own challenges if you haven’t worked with surface mount before.
« Last Edit: September 30, 2020, 04:09:16 PM by rackmonkey »
Whether you think you can or you think you can't, you're probably right.

Whoops

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #9 on: September 30, 2020, 07:17:46 PM »
Some points about the situation:

1) Why do you think do you have a problem with the U411 in your Mic pre?
In many years of fixing and repairing audio equipment I never had a broken JFET or to replace one for malfunctioning.

2)Contact Presonus, they might be able to supply the part. I'm sure somewhere in Presonus they have quite a lot of those JFETS as they buy in bulk and keep quantities for future repairs

3) you can buy the U411 from ebay, why dont you buy it from there?
https://www.ebay.com/itm/2-PCS-DUAL-N-CHANNELL-JFET-Transistor-Siliconix-TO-71-CAN-6-U441-gold-leads-/362691789045

4) contact Vishay/Siliconix and Linear systems enquiring for old stock or sample parts.

5) If you want to fix it fast,
get a pack of 10x 2Sk170:

https://www.banzaimusic.com/2SK170BL.html

Choose 2 that are matched (or most matched), glue them like in the picture I posted, solder them to the pcb and try them out.
If they work well move on to recording and having fun, consider it solved


Khron

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #10 on: October 01, 2020, 12:10:59 AM »
2) Yeah, I kinda doubt that - they couldn't even be bothered to provide a ready-compiled firmware file for an interface (that would've costed nothing, and it's not even the source code).
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

rackmonkey

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #11 on: October 01, 2020, 12:12:57 AM »
Good points/suggestions, with the notable exception of #3. Or at least that one should have an asterisk next to it. Fake though-hole JFETs are rampant on eBay. I’d avoid any chinese sources. Often they are factory rejects or simply re-labeled parts. Just do a Google search to get a sense of the scale of the problem. I have a small box or maybe 100 or so JFETs sourced from many separate purchases on ebay that test so far outside of their expected Vgs:Id curves to make it certain that they are not what they are labeled as. Was burned many times, with plenty of wasted time on projects to show for it.

That said, you can get real, vintage JFETs on ebay. But you have to be savvy in how you select sellers. Actual pictures help. Estate finds are usually good.

Edit: the link Whoops posted points to what look like a decent bet on vintage U441s.
« Last Edit: October 01, 2020, 12:18:30 AM by rackmonkey »
Whether you think you can or you think you can't, you're probably right.

gyraf

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #12 on: October 01, 2020, 03:58:27 AM »
to 1) I've replaced dozens of broken audio-switching jfets in our big consoles over the years, and a couple of mic front-ends too. But you're right, failure is rare in linear input stages.

/Jakob E.
..note to self: don't let Harman run your company..

Whoops

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #13 on: October 01, 2020, 07:55:28 AM »
2) Yeah, I kinda doubt that - they couldn't even be bothered to provide a ready-compiled firmware file for an interface (that would've costed nothing, and it's not even the source code).

It´s always the first thing I try, contacting the spare parts department of the manufacturer and 70% of the time they give for free or sell me the part.
You don't incur in any expense in trying

Whoops

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #14 on: October 01, 2020, 07:58:10 AM »
Good points/suggestions, with the notable exception of #3.

That said, you can get real, vintage JFETs on ebay. But you have to be savvy in how you select sellers. Actual pictures help. Estate finds are usually good.

Its only 10 bucks, it's not a big risk.
I would just order it and try it, if it works fine it's a win, if doesn't work I would return it ans ask an ebay return.
pretty simple for me
But I'm a really practical person...

Whoops

Re: Need help finding a replacement for old no longer manufactured JFET.
« Reply #15 on: October 01, 2020, 08:00:25 AM »
to 1) I've replaced dozens of broken audio-switching jfets in our big consoles over the years, and a couple of mic front-ends too. But you're right, failure is rare in linear input stages.

/Jakob E.

I was just asking because the op didnt tell us what the problem might be, and in the end the problem could be somewhere else and not in the dificult to find dual JFET and we could for sure provide some help in fixing the issue.

Thank you Jakob


 

Related Topics

  Subject / Started by Replies Last post
2 Replies
1582 Views
Last post May 11, 2005, 04:41:03 PM
by dr. foster
3 Replies
1685 Views
Last post September 29, 2005, 08:06:53 PM
by mcs
0 Replies
956 Views
Last post April 12, 2007, 04:11:51 PM
by versuviusx
16 Replies
2922 Views
Last post October 23, 2011, 02:00:53 PM
by amorris