School Me On JFETs! (please) :) Sourcing, Substitutes, Etc

[Ginsly]

There are some upcoming builds that call for Jfets, and I've never used them before. I have a few through-hole J201s I got from Small Bear right before I started building last Dec, but I haven't set up a tester for them yet (no DCA75 sadly).

First - what is my best bet for Jfet sourcing these days? It sounds like SMD parts on a through-hole adapter are the way to go (?), but I'd love to hear some suggestions for low-hassle part numbers and where best to get them. I see that PedalPCB offers some already soldered to an adapter, and Aion does as well. I've seen J113, J201, and 2N5457 mentioned the most - not sure if they're more or less interchangeable. I assume places like Amazon are terrible for Jfets.

Secondly, I have a couple After Blaster 3pdt boards (courtesy @Feral Feline!) that call for a J113 (or J201, 2N5457, MPF201). In some cases I actually want the boost at the end of the circuit to NOT be clean, but to make a fuzz fuzzier, not just louder. Since I haven't worked with Jfets before, I'm not sure if I can expect one to do that. I'd love to use a BJT instead, but it's specifically set up for Jfets:

Is there any way to somehow use a BJT in place of the J201s I have? I've heard that @Chuck D. Bones might have some insight...

One of the PPCB Muffin Crumbs is similar and DOES use a BJT, but setting it up is a little less intuitive (especially powering it).

Thanks for any insights in this next step!

 

[spi]

From @Chuck D. Bones, who often shares his wisdom here:

JFET Shootout | PedalPCB Community Forum

JFET Biasing - part 1 | PedalPCB Community Forum

 

[Ginsly]

From @Chuck D. Bones, who often shares his wisdom here:

JFET Shootout | PedalPCB Community Forum

JFET Biasing - part 1 | PedalPCB Community Forum

Thanks! Yep I did look through some of the jfet posts here, but it gets SO complicated so quickly.

It's obviously a tricky component to deal with, and I'm really trying to find the "dummy's" way in. I'm not quite sure where to start, as all of the calculus makes me want to run back into the arms of a BJT! Ha...

 

[spi]

This article was a big help for me: A closer look at the Fetzer Valve (runoffgroove.com)

 

[Ginsly]

This article was a big help for me: A closer look at the Fetzer Valve (runoffgroove.com)

It'll take a while for that info to fully sink in, but it's a great start.

In the meantime, since you work with them- what kind do you like to get, and from where? And is it ever possible to replace a jfet with a bjt (with some other modifications)?

 

[spi]

I recently got j201s and 2n5457 from PedalPcb (smd).

Other vendors I trust are tubesandmore and stompboxparts. They have some limited options for jfets, but carry the ones you'll find in pedals.

I would trust mouser but I never order from them because I'm usually ordering from places that focus on pedal parts.

Take a look at this article: Basic Buffers (muzique.com) It shows a few buffer arrangements, some with jfets and some with bjts. You can see that replacement will work for buffers in some cases (with some resistor value swaps). However, the boost you have is in a different arrangement. I don't know if the same applies.

Do you have a breadboard? One way to find out is to try it yourself.

 

[Ginsly]

I recently got j201s and 2n5457 from PedalPcb (smd).

Other vendors I trust are tubesandmore and stompboxparts. They have some limited options for jfets, but carry the ones you'll find in pedals.

I would trust mouser but I never order from them because I'm usually ordering from places that focus on pedal parts.

Take a look at this article: Basic Buffers (muzique.com) It shows a few buffer arrangements, some with jfets and some with bjts. You can see that replacement will work for buffers in some cases (with some resistor value swaps). However, the boost you have is in a different arrangement. I don't know if the same applies.

Do you have a breadboard? One way to find out is to try it yourself.

I take it you got smd J201s and 2N5457s already on adapter boards?

I actually need to order from Tubes & More, and have been looking at their jfets. Seems a little pricey there, but I don't know what's reasonable to pay for jfets yet...

That article on buffers is interesting, and they do indeed mention subbing a bjt for a jfet. Hmm.

Since it's a footswitch-mounted pcb/boost I assume I'd need to pretty much have everything else done and THEN run jumpers from the jfet pads to a breadboard in order to test a bjt...

 

[spi]

I take it you got smd J201s and 2N5457s already on adapter boards?

I actually need to order from Tubes & More, and have been looking at their jfets. Seems a little pricey there, but I don't know what's reasonable to pay for jfets yet...

No, I don't buy them on adapter boards (I have some adapter boards I got from oshpark that I can use if I need to, but many PCBs now have the SMD pads on them).

Some Jfets are getting overpriced in TO-92 packages (especially j201), which is why I buy them in SMD. I wouldn't pay over $1 for one. Some like the j113s and 2n5458 can still be found under or close to $1.

 

[Ginsly]

No, I don't buy them on adapter boards (I have some adapter boards I got from oshpark that I can use if I need to, but many PCBs now have the SMD pads on them).

Some Jfets are getting overpriced in TO-92 packages (especially j201), which is why I buy them in SMD. I wouldn't pay over $1 for one. Some like the j113s and 2n5458 can still be found under or close to $1.

I really, really appreciate you chiming in. This is all helpful!

If I wind up getting some smd jfets, it sounds like J201, J113, and 2N5457 are the ones to look at- correct? You also mentioned 2N5458, which I haven't seen mentioned as much.

I would likely get them pre-attached to adapters, but if not - where do people go for those? I'm not familiar with oshpark, and have never had pcbs made. Barely 5 months into building! I assume its kind of like JLC which people also use for this kind of thing..?

 

[Passinwind]

I really, really appreciate you chiming in. This is all helpful!

If I wind up getting some smd jfets, it sounds like J201, J113, and 2N5457 are the ones to look at- correct? You also mentioned 2N5458, which I haven't seen mentioned as much.

I would likely get them pre-attached to adapters, but if not - where do people go for those? I'm not familiar with oshpark, and have never had pcbs made. Barely 5 months into building! I assume its kind of like JLC which people also use for this kind of thing..?

OSH Park ~

oshpark.com

If you find something you want in the shared boards section it's as simple as clicking and paying, then waiting about two weeks for your order to show up. They're a US based vendor and so are the board fabrication houses they contract with. For very small boards like adapters their pricing gets more attractive due to the free shipping.

But you could just go here and also use FETs sourced from PPCB: https://www.pedalpcb.com/product/sot23adapter/

And IMO the sooner you start to come to grips with soldering surface mount parts yourself, the better.

 

[Ginsly]

And IMO the sooner you start to come to grips with soldering surface mount parts yourself, the better.

Thanks for the oshpark info- seems like it is indeed like jlc, though there may be differences I’m not aware of.

I’m certainly willing to try soldering surface mounted parts- seems tricky, though! I assume you mention this because through-hole components will stop being made in the near future?

 

[Passinwind]

Thanks for the oshpark info- seems like it is indeed like jlc, though there may be differences I’m not aware of.

I’m certainly willing to try soldering surface mounted parts- seems tricky, though! I assume you mention this because through-hole components will stop being made in the near future?

Almost none of my favorite opamps are even available as through-hole parts right now, FWIW. If you start with the larger part sizes and invest in a few properly small soldering iron tips it gets easier pretty quickly, I'm over 70 and do fine hand soldering many things without even using magnification. Torching a few 60 cent parts or whatever might be annoying, but I think you'll find it very worthwhile in the longer term.

OSHpark does have some (arguable) quality advantages over the default JLCPCB spec, especially on the graphics side, but IME it rarely matters all that much for what we're doing here. There are many other decent board vendors out there besides those two as well.

 

[Feral Feline]

Here's a thort...

For boards that have both SMD pads and THD, in future I'll go for the adapter-boards with SMD-JFET soldered to the adapter board — socket the THD on the main PCB and then I can still audition diffferent JFETs.


I may have overcooked a SMD JFET while trying to direct solder it to the main board...

 

[Aentons]

You don't need smd adapter boards, just tack solder clipped resistor legs on and you are good2go

 

[Ginsly]

For boards that have both SMD pads and THD, in future I'll go for the adapter-boards with SMD-JFET soldered to the adapter board — socket the THD on the main PCB and then I can still audition diffferent JFETs.

Yep, this is 100% what I'd do. Sounds like smd-on-adapters are actually more reliable (and possibly cheaper, even with the adapter).

Heh, your pic is exactly what I expect to happen when I try to solder teeny tiny specks... we'll see!

@Aentons whoa! Not familiar with tack soldering, and a quick search led to people doing stained glass! ha...

 

[Ginsly]

I'll put some sockets in here, but... is it ridiculous to think I can try a BJT here when it calls for a JFET?? I'm not even sure how the pinouts would correlate... Don't wanna go up in smoke!

 

[Feral Feline]

You'll need to do some kajiggering if you want to stuff a BJT where the JFET goes — above all, MIND THE PINOUT!

Compare the schematic of GuitarPCB's AfterBlaster (AB)...

... to Jack Orman's AMZ schematic of a BJT Booster ...

The AMZ schem is basically the last stage of a Muff, so reference PedalPCB's Muffin Crumb Tone Recovery Stage in the Crumb's build doc.
As can be seen, the only missing piece of the puzzle is the BJT's R2.

So I'd sub in a cap or cap and resistor for the AB's R1 (C1 on the AMZ schem).
Then I'd probe the AB board to see where I need to bodge in the AMZ's R2 to the AB-PCB. (add resistor to AB's top of R2 to top of R4 on the schematic)

Play around with the Crumb's various values for Preamp, Clipping and Tone-Recovery stages *(ie Muff schematics as a guide) to find the tone/results I'd want.


To reiterate, MIND THE PINOUT !

 

[Ginsly]

You'll need to do some kajiggering if you want to stuff a BJT where the JFET goes — above all, MIND THE PINOUT!

Gotcha! There is a little "D" at the top pin of the jfet in the AB diagram - I assume this means "drain"? Otherwise I'm not sure how to determine the pinout... I did, however find this:

Based on this, it looks like that top pin must be Drain, as it leads to the 9v power source like a Collector would in a BJT. Guess I know which way to insert a BJT now- Excellent! Regarding biasing a jfet with the trimmer - seems like I would set up the entire AB 3pdt board and main circuit pcb, power it up, insert the jfet and then use a mm with red on drain and black on "ground" to measure... correct? Does that mean any ground at all on the AB board? Apologies- again, this is a first for me!

So I'd sub in a cap or cap and resistor for the AB's R1 (C1 on the AMZ schem).
Then I'd probe the AB board to see where I need to bodge in the AMZ's R2 to the AB-PCB. (add resistor to AB's top of R2 to top of R4 on the schematic)

It looks like you posted the V1 AB schematic, here's the most recent one (below, 2021). Things are a little different (he added a bias trimmer and adjusted R4 to 33k to remove attenuation from the volume pot) so I'm wondering if your additional cap/resistor suggestion would change... And would the added cap & resistor just be in series? Trying to visualize how/where I would cram it onto this tiny board - I've yet to probe a board, so I need to look up how to do that. Still, I wouldn't really know what to look for when determining a good cap/res insertion point on the AB... Hmm. Thanks, this is very helpful!!

 

[jwin615]

SOT23-3:

https://a.aliexpress.com/_mqvWUWq

For tssop ssop dips:

https://a.aliexpress.com/_mKAWWh4

 

[Feral Feline]

AFTERBLASTER CONVERSION TO BJT

Okay, I slapped these together quickly, so check them with the physical board and a multimeter set to continuity.

Values are suggestions only, play around with the INPUT CAP at 100n for guitar 220n for bass. Play with C1 22µF, ie ditch it altogether or try smaller values... I don't know if how the circuit will behave with it, but if in doubt — DITCH C1!
R5 I striped as 470k, but you could go 390k—510k-ish.
BJT Could be 3904, 5088, 5089, BCxxx etc — just remember to twist the legs around for the correct pinout on the PCB.
[Edit: Depending on what's feeding the AfterBlaster, you may not need a Cap — ie the output cap of the board preceding the AB works to filter out the DC. ]




You could also mount that resistor on the component side with the other bits, but I think it's good where I put it. Out of the way ...


Gotta go play trombone...