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

[Feral Feline]

@Ginsly
I didn't have time yesterday to look into it, but I vaguely recalled some BJTs that have wacked pinouts (compared to other BJTs).


Here's a BJT with a TO-92 package that has a BEC-pinout:

Mouser Datasheet for FAIRCHILD KSP10 PDF !
OnSemi took over Fairchild and lists the KSP10 as still active, here's the OnSemi KSP10 datasheet PDF; so you should be able to get some KSP10 from Mouser or elsewhere.
Since I'm already at it, Mouser has two versions:

https://www.mouser.com/c/?q=KSP10BU&exact=true

https://www.mouser.com/c/?q=KSP10TA&exact=true

The BU version has 7,000+ straight legs in stock, and is 35¢;
The TA version has 7,000 pre-bent legs in stock, cheaper at 32¢.


As per this thread on Electronics Stack Exchange, I also recalled there being Japanese Epitaxial Silicon BJTs with the BEC / CEB pinout;
that's also where I found reference to the KSP10 above. In the thread, the KSP10 is compared to a 2N4401, here's the datasheet PDF.



Further to the 4401, the original Intersound IVP Preamp called for a few 4401 — Aion's IVP take subs out the 4401 for a 2N3904, a very-common middle-range BJT, one of my favourites due to its low cost and ubiquitous availability.
Other circuits with 4401: PPCB's Duophase and Loft Fuzz, Moonn's Dice, EAE Beholder, ApeTone's 280KG Gorilla, Madbean Glasshole and Retrograde, LG Hazy Octave, GPCB OKF... loads.






Years ago, before Barbershop PCBs were readily available and before I knew what I was doing (alas I still don't know, but...), in 2018 I built a pseudo Barbershop on a GuitarPCB Red Special. I had noticed the basic skeletons of the two circuits' schematics were the same. The notable difference is in the transistors...

Barbershop is JFET > JFET > BJT
(J201s x 2 and a 2N2222)

Red Special is BJT > BJT > JFET
(2N5088, 2N3904, and 2N5457

I found the 2SK117 had the pinout I needed for putting JFETs in the Red Special's BJT positions, but then I had to bend legs of a 2N2222 to fit the BJT in Q3-JFET position of the RS.
My research revealed the 2SK117 is a pretty good sub for the J201, and now 6 years later I find the KSP10, a comparable sub for the 2N2222 — it may put an end to the bent legs!



I'll be picking up some KSP10TA myself, next Mouser order, and then hopefully I won't have to mangle legs on Q3 of future Red Special Barbershop builds.


Meanwhile, I'll hunt a while longer for some more BEC-pinout BJTs.
Please let me know if you find any others.

 

[Ginsly]

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!

WOW! Jeez, man - I can't believe you plotted this out! Seeing this kind of situation sketched out really, really helps - I can't thank you enough!! I'll certainly keep in mind that C1 may not be necessary at all, or could be a much smaller value - sounds like I'd know based on how noisy the pedal is..?

[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. ]

I'm thinking of attaching this to a Trumpeter to kind of sort of approximate a Baron Samedi... that's part of why I'd like this added, 3rd gain stage to have some grit to it, since the BS does indeed use 3 BJTs.

BJT Could be 3904, 5088, 5089, BCxxx etc — just remember to twist the legs around for the correct pinout on the PCB.

Ahhh I see. In the schematic you modified it looked like the pinout would be C-B-E, but on the board itself it looks like it works out being B-E-C... huh, why would that be? I'd think they would go in the same order as the schematic, unless one of them is incorrect... I'm sure this makes perfect sense, and I'm just too green to get it yet! Ha...

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 ...

Adding this resistor between R2 and the trimmer, would I still be installing the Bias trimpot at all? I thought about making it an external knob for extra craziness, so I'd like to keep it in the mix unless it's going to just complicate things (too late! ha)...

I didn't have time yesterday to look into it, but I vaguely recalled some BJTs that have wacked pinouts (compared to other BJTs).

That post is a great start when it comes to non-standard Si pinouts, and I'll definitely be looking into what else is out there. For the occasional situation like this where they're needed, I don't mind twistin' some legs though! Thanks for ALL of this- unreal, man!

 

[Feral Feline]

WOW! Jeez, man - I can't believe you plotted this out! Seeing this kind of situation sketched out really, really helps - I can't thank you enough!! I'll certainly keep in mind that C1 may not be necessary at all, or could be a much smaller value - sounds like I'd know based on how noisy the pedal is..?

I'm thinking of attaching this to a Trumpeter to kind of sort of approximate a Baron Samedi... that's part of why I'd like this added, 3rd gain stage to have some grit to it, since the BS does indeed use 3 BJTs.

Ahhh I see. In the schematic you modified it looked like the pinout would be C-B-E, but on the board itself it looks like it works out being B-E-C... huh, why would that be? I'd think they would go in the same order as the schematic, unless one of them is incorrect... I'm sure this makes perfect sense, and I'm just too green to get it yet! Ha...

Adding this resistor between R2 and the trimmer, would I still be installing the Bias trimpot at all? I thought about making it an external knob for extra craziness, so I'd like to keep it in the mix unless it's going to just complicate things (too late! ha)...

That post is a great start when it comes to non-standard Si pinouts, and I'll definitely be looking into what else is out there. For the occasional situation like this where they're needed, I don't mind twistin' some legs though! Thanks for ALL of this- unreal, man!

Addressing each point above:

C1 reveals my lack of knowledge; I've a vague idea of why it's included in the JFET boost, but not sure why I would want it or not in a BJT boost. Adding it will change the amount of gain you get and size of it affects what frequencies get boosted.

By all means, add the AB-BJT to your trumpeter. If you want it to distort, look at other BJT one-transistor circuits that are known to get some grit and look at the values of everything feeding that transistor. EQD BELLOWS (PedalPCB Barrage OD) for instance, will get you the grit you seek AND it has the AB's "C1", that is to say it has a 100µF cap coming off the Barrage's Emitter.

The schematic CBE is correct, and the BEC of the board layout is correct — I'm glad you noticed that they differ. The schematic is just a representation of the real world; how things connect may not correlate with the physical properties of what you're working on. A traffic circle on a map probably won't tell you whether the circle is uncontrolled or also includes traffic lights...

Just to be clear, the 470k I added between the trimmer and R2 is NOT replacing anything, but rather adding to what has now become essentially a Muff's BJT-output stage.
You could breadboard the circuit to figure out a fixed resistor value instead of the trimmer, or stay with the trimmer for set and forget or...
If you plan on adding the trimpot as an external control, I would add a small resistor in series with it, so that when the external knob is at minimum, you still have a working functional circuit. If you don't have a minimum resistance, then the BJT is either going to blow up or not work at all — test it on your breadboard with a 2N3904, and let me know how which way the sacrifice goes — does the 3904 burn up or does it just sit there waiting for some resistance and then get back to work?

There are those with far more and better knowledge than mine, but I'm happy to share what little I've got.
You're welcome.

 

[Ginsly]

@Feral Feline Incredible! Ah, good thing I asked about the pinout discrepancy- I figured it MUST be correct, but didn’t know why that would be.

In cases like this, I assume I’d have to just look up the pinout of the pcb-maker’s recommended jfet(s) in order to determine the pinout on the actual board. It’s so odd that the schematic and physical pinout don’t correlate! Guess it must be something with jfets, as I have‘t experienced that yet with bjts.

Very good to know that I’d install a 470k resistor in addition to the normal trimmer/pot. In fact- is this essentially the 470k resistor in the Baron Samedi that winds up being the DEATH pot instead? Hmm in that case wouldn’t I make the additional resistor 47k and the trimmer/pot 500k like Aditya had indicated? Maybe that’s all wrong… I REALLY want to get that super pinched sound the BS can do, but maybe this isn’t where that’d happen… Gotta check the schematic!

I realize adding this to a Trumpeter certainly isn’t going to be a BS, but I’m trying for something in that ballpark with Voltage Starve (which the Trumpeter already has) and a transistor Bias knob (which the AB seems to add, along with the needed 3rd gain stage). We’ll see what kind of monstrosity is born! Ha…

Huge thanks as always.

 

[Feral Feline]

I've done some more snooping for BEC pinouts and instead I'm getting things like BEC corporation's website, an online Basic Electronics Course ...

It's a little frustrating, as I know there must be some more BEC TO-92s out there (Japanese ones, almost certainly).


There's a BF199 I found:

"The BF199 is an RF transistor that can be utilized in a wide range of RF applications, including high-frequency radio and television applications, AM oscillators, IF amplifiers, and so on.
Aside from that, it can be utilized for audio purposes."

Great, it can be used for "audio purposes" — forgive my ignorance, but ... do we really want an RF-inducing type trans in pedal builds? Usually we're trying to eliminate RF-interference !
(PDF DATASHEET)


And The Seach Goes On
Yeah the search goes on...

Search online keeps pounding
Transistor gain and pinout
B E C , B - E - C


And The Seach Goes On
Yeah the search goes on...

WIKIPEDIA...

There is no standard pinout for the TO-92. The American BJTs use the E-B-C pinout while their Japanese counterparts use the E-C-B pinout and some RF devices use the B-E-C pinout.

Well there sure has been a lot of talk about BJT in a thread-title requesting "School Me On JFETs! (please) Sourcing, Substitutes, Etc"

 

[Ginsly]

I've done some more snooping for BEC pinouts and instead I'm getting things like BEC corporation's website, an online Basic Electronics Course ...

Every time I try to track a UPS package I have to scroll past uninterruptible power supply sites...

Well there sure has been a lot of talk about BJT in a thread-title requesting "School Me On JFETs! (please) Sourcing, Substitutes, Etc"

Haha... that's good! I'm still trying to sum up the similarities/differences between the two, so it's certainly helpful!