3 ms·

AoE and AoE X has a bit on TIAs as well, their "final form" circuit idea enhances the basic JFET follower idea with an additional emitter follower to reduce sou

AoE and AoE X has a bit on TIAs as well, their "final form" circuit idea enhances the basic JFET follower idea with an additional emitter follower to reduce source impedance and by AC-coupling the compound follower's output they get to set favorable DC working points. The tricky bit is going to find a suitable replacement for the BF862.

deleted 2y ago
[deleted]
jeffbee 2y ago
Depends on the critical parameters, but 2SK2394? You can try to source old JFETs but all of the ones advertised online are fake.
- formerly_proven 2y ago
  It has been a couple years, but iirc the BF862 back then had a pretty unique combination of low capacitance, low e_n and a low 1/f knee. The 2SK2394 is also earmarked for use as an AM radio amplifier, same as the BF862, which probably also explains why these went from jellybean to rarity some time ago...
CamperBob2 2y ago
Phil Hobbs has also written a lot about photodiode bootstrapping, and he was also a very unhappy camper when the BF862 went EOL. Anyone working in this area should check out his book (see https://electrooptical.net/ https://electrooptical.net/), which is very much in the same spirit as AoE. I used to read a lot of posts by Phil on Usenet via Google Groups, before Google decided they had better things to do. For that matter, I have a feeling Michal (lcamtuf) has a book or two in him that could stand up next to Hobbs and Horowitz/Hill on the shelf. Super impressed with his work over the years. (Many may recognize him as the 'Guerilla Guide to CNC' guy, which has been linked on HN several times.) CPH3910 may be worth considering as a BF862 replacement. I don't recall the part number but there's also a dual CPH3910 in a 5- or 6-pin SOT package that could be used with the transistors in parallel.

3 ms·

AoE and AoE X has a bit on TIAs as well, their "final form" circuit idea enhances the basic JFET follower idea with an additional emitter follower to reduce sou

by formerly_proven 2y ago

deleted 2y ago
[deleted]
jeffbee 2y ago
Depends on the critical parameters, but 2SK2394? You can try to source old JFETs but all of the ones advertised online are fake.
- formerly_proven 2y ago
  It has been a couple years, but iirc the BF862 back then had a pretty unique combination of low capacitance, low e_n and a low 1/f knee. The 2SK2394 is also earmarked for use as an AM radio amplifier, same as the BF862, which probably also explains why these went from jellybean to rarity some time ago...
CamperBob2 2y ago
Phil Hobbs has also written a lot about photodiode bootstrapping, and he was also a very unhappy camper when the BF862 went EOL. Anyone working in this area should check out his book (see https://electrooptical.net/ https://electrooptical.net/), which is very much in the same spirit as AoE. I used to read a lot of posts by Phil on Usenet via Google Groups, before Google decided they had better things to do. For that matter, I have a feeling Michal (lcamtuf) has a book or two in him that could stand up next to Hobbs and Horowitz/Hill on the shelf. Super impressed with his work over the years. (Many may recognize him as the 'Guerilla Guide to CNC' guy, which has been linked on HN several times.) CPH3910 may be worth considering as a BF862 replacement. I don't recall the part number but there's also a dual CPH3910 in a 5- or 6-pin SOT package that could be used with the transistors in parallel.