J201 Sourcing

[freshmex18]

I have a few projects lying around that I tried to build a year or so ago and all of the J201 SMDs I ordered would not work in the circuits.  Wondering where y'all source your J201s that are reliably within spec.  I really want to get at least some of those pedals finished.  Should I be ordering a much larger amount than I really need to account for out of spec ones?  I have yet to actually get any circuit requiring J201s to work so....

Thanks

[antonis]

Have you tried alternatives, like 2N5457, 2N3819, 2N5484-5-6, 2SK369/371 or BF256B..??

[temol]

all of the J201 SMDs I ordered would not work in the circuits.

Can you elaborate on this? What's the issue with SMD's? Many of us switched to SMD J201 (MMBFJ201) because most of through hole J201's available lately are out of spec/fake/rebranded.

[Ben N]

This is kinda the story of JFETs, even when supply/obsolescence was not an issue.

[PRR]

...would not work...

Not much of a clue. Did you measure any voltages?

[amz-fx]

all of the J201 SMDs I ordered would not work in the circuits

The smt and th parts are exactly the same chip, just packaged differently. There is no difference, if you are getting them from a reliable source.

You should check the pin configuration as they are different on the two packages.

If you bought them on Ebay, they may not even be jfets! 

regards, Jack

[danfrank]

I'm not affiliated but here ya go:

https://lectric-fx.com/product/jay-fetz-singles-matched-pairs-quads/

Pick "J201" in the drop down menu.
These are legit and work but make sure you get the pin out correct.

[freshmex18]

Wow, so many replies so quickly.

I bought SMDs from PedalPCB and Mouser - about a dozen total within a month of each other - and none of the circuits would work with them in it.  I got the I could trace signal with an audio probe a good way through the circuit and then by Q3 or Q4 there wouldn't be any sound anymore.  There would be sound going into the J201 but not coming out.  I tried swapping with others but no go.  I tried them in builds of a ROG Supreaux, JHS Twin Twelve, ROG Uno, Wampler Plexidrive, ROG Brittania, and a few others I can't remember.  Just would not work no matter how I tweaked the twimmers.  (I'm writing this from memory as it's been a year since I binned those builds)

I have not tried alternatives.  Are any of those alternatives better than others at approximating the same sound as J201s?

I have a handful of adapter boards for SMDs from PedalPCB so using SMDs is no issue.  I just want to be able to actually use them

I'm pretty new to pedal building but have a dozen successful vero and kit builds, but I do not fully understand the nuances of how the science works.  I can plug and play but couldn't design a circuit myself.  So please bear with me as I try to wrap my head around all of this

[idy]

I would do some reading and build a testing jig. Confirm pinout. Find out what you have....
Do you know how a J201 is supposed to act with a meter?

[freshmex18]

I did build and use this but honestly I don't know what to compare the readings to other than I should find ones that are close to match them

http://tagboardeffects.blogspot.com/2012/07/greatly-improved-jfet-matcher.html

[antonis]

Do your projects call for matched FETs..??

[garcho]

No offense, but this most likely has to do with your wiring/board layout, or something along those lines, and not anything at all to do with whatever semiconductor you're using. You should read the troubleshooting/how to ask for help sticky. Pics, voltages, wiring diagrams, etc., Long story short, SMT is basically better than through-hole in every way, other than ease of soldering by hand a la DIY stuff. Even then, once you get used to it, it's not that hard, depending on the packages. If I had a dollar for every time someone started a thread about FET devices "not working"...

[idy]

The circuits you mention do not require matched FETs, just ones that will amplify. What results did you get from the tester? It's worth doing it again if you still care about those projects. JFET "amp-in-a-box" circuits can sound really good.

Do you have a breadboard to set up a simple JFET buffer or booster? All those things are is cascaded boosters (and a tone stack..and, well some have things like 'mu amps'...)

[Rob Strand]

There's a difference between matching and extracting JFET parameters.

If a jig measures the JFET parameters you can also use the numbers for matching.

Jigs don't always measure consistently.  Noise can effect the results.   Some can even oscillate with low RDS_on switching JFETS.  That means the measurements are rubbish.  They can even measure consistently bad.   Powering from battery helps.

Matching jigs only requires a magic number to be produced which represents a match.

RG's jig produces VGS values which are good for matching but the VGS values are somewhat less than the VP *parameter*.   RG's jig measures at higher currents and the jig has lower impedances so it is less likely to produce numbers affected by noise.

[freshmex18]

None of the projects have called for matched JFETS.

Every one of those projects I have built multiple times, throwing out the old vero and making a new one and no good.  For the ROG Brittania, I even ordered the 1776 board after my vero build failed and it still didn't work.  So it has to be the components.

I honestly don't know enough to build from a breadboard.  I can follow a vero layout but converting it to a breadboard or even taking a schematic and figuring out how to get it on a breadboard is currently out of my ability.  Perhaps that disqualifies me from being able to build these particular projects then and I should stick with ones I have been successful with - basically everything I have built that doesn't involve J201s

[anotherjim]

Try something simple like preamps...
https://tagboardeffects.blogspot.com/2014/05/a-pair-o-preamps-echoplex-and-tillman.html
And, just in case, don't forget the Gate of the smd FET is the *middle pin and it doesn't matter which is the source or drain just get the gate in the right place.
* some adapters correct this to one end.

[antonis]

basically everything I have built that doesn't involve J201s

J201s are (were) all-around general purpose small signal amplifiers..
(some people even used them as switchers..)

Due to their notorious parameter wide spread, they called for conservative design circuits where parameters particular values should be not taken into account..
(or to be widely overspread..)

What I'm saying is what idy already said about JFETs non-working circuits..
(particular device rarely is guilty for that..) 

[vigilante397]

I'm writing this from memory as it's been a year since I binned those builds

Sounds like time to revisit them. PedalPcb and especially Mouser are both reliable sources for JFETs, neither one would sell you counterfeits. Your problem is not the quality of the parts.

[rankot]

None of the projects have called for matched JFETS.

Every one of those projects I have built multiple times, throwing out the old vero and making a new one and no good.  For the ROG Brittania, I even ordered the 1776 board after my vero build failed and it still didn't work.  So it has to be the components.

I honestly don't know enough to build from a breadboard.  I can follow a vero layout but converting it to a breadboard or even taking a schematic and figuring out how to get it on a breadboard is currently out of my ability.  Perhaps that disqualifies me from being able to build these particular projects then and I should stick with ones I have been successful with - basically everything I have built that doesn't involve J201s

How EXACTLY it doesn't work? Not work at all, or works, but not as expected?

[antonis]

How EXACTLY it doesn't work?

Are you some tough internal auditor guy or what, Ranko..??