Good morning everyone,
Due to the shortage of good, quality, non-fake, reasonably priced TO-92 JFETS like J201 and 2n5457, I am considering their (supposedly) SMD equivalents - MMBFJ201 and MMBF5457, respectively.
I know I will need a conversion board in order to use them in a THT environment, like most pedal builds, and this is not a problem for me.
My questions are:
1. Are they truly FULL equivalents? Can SMD versions be used instead of TO-92 versions? Will they work the same? Any mods needed to the rest of the shematic to accomodate for the change in case style?
2. I've heard the tolerances in SMD parts are tigher. Does this mean I will need fewer, say, MMBF5457's to find a VgsOFF-matched quartet for a Phase 90 (Nom Nom) than I would need 2n5457's?
3. I've heard that Source and Drain are interchangeable on both 201 and 5457. Does this really mean I only need to make sure the Gate (left pin in TO-92, top one in SMD) is connected correctly, and the rest can go wherever?
4. Anyone had ay luck using SMD 201's and 5457's from Tayda? Any problems with those?
Thanks in advance!
1) Yes, fully equivalent. Its the same guts, just in a different package. (note this is in regards to pedal work, they do have somewhat different thermal tolerances given the different form factor, so not 100% interchangeable in ALL uses, but for our purposes its near enough)
2) I've heard this rumor too, but according to datasheets the thru-hole and SMD parts have the same tolerances. I'd test in either case until I had enough empirical data to say otherwise.
3*) Somewhat ancillary, but I always use adapter boards with my SMD fet's so I treat them identically to the thru-hole parts. That said, the 5457 and 201 are symmetrical, source and drain are swappable.
4) Haven't had a reason to try theirs yet. Sorry.
Regarding your second question, what seems to be common sense is high consistency between parts of the same reel (which in my experience is similar in through-hole ones, it's just harder to get them from the same reel)
MMBF5457 are end of life. Which sucks tbh.
A suggestion and what I did was bought like 10 of the TO-92s from Smallbear and use them to test the board. Once running I replace them with the SMDs. I've always been afraid of putting to much heat on the SMDs and burning it up.
I've ran through a bunch testing them and they tested no different than the TO-92s. I had to go through 20 or so to find 3-4 that matched.
I thought General Guitar Gadgets sold matched sets but they don't anymore. I know he matched some 5952s for me when I asked. Also see that he is selling 5457s for .36 each TO92s.