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In a previous question I asked for a replacement for the J402/LS3954 dual JFET that has gone out of production and increasingly expensive. (Mouser has them for $23 right now, what a deal) and I came across the BSR58 single JFET which is on average about $0.10 from China. I don't mind electrically matching the two with a multimeter since the application isn't crucial (to me, anyways).

Comparing the two datasheets, is the BSR58 a suitable replacement for the J402? I'm not at all familiar with FETS or their specs so any help is appreciated.

BSR58

2N3954

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  • \$\begingroup\$ It’s only suitable if it performs the function with the same performance in your target circuit. \$\endgroup\$
    – Andy aka
    Apr 23, 2020 at 21:19

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Compare the Idss 0.5~5mA vs. 8~80mA, these parts are very, very different, even if the junction temperature matching is not required in your particular application.

I see the Linear Systems LS3954 for a lot less than $23, so maybe shop around if you're not up to a full re-design.

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  • \$\begingroup\$ I'm using these parts in a small-scale production of PCBs, and I will need hundreds of them. Unless the kickstarter really takes off, I'd prefer a cheaper option as I can't have a super high manufacturing cost. I need 6 of them per unit. \$\endgroup\$
    – zvolk4
    Apr 23, 2020 at 22:30
  • \$\begingroup\$ Also, the application for these is audio, and the purpose is to provide a clean audio waveform from an oscillator. \$\endgroup\$
    – zvolk4
    Apr 23, 2020 at 22:31
  • \$\begingroup\$ The person who designed the circuit should be able to advise. It's quite possible for bad side effects (such as oscillation or clipping) to occur by substitutions, even if the circuit was well-designed to begin with. \$\endgroup\$
    – Spehro Pefhany
    Apr 23, 2020 at 22:36
  • \$\begingroup\$ Well, the two people I know who have passed away many years ago, and I haven't been able to get in contact with anyone else. Since the prototype for this thing will only cost me a few bucks in parts it's not a bad idea to do trial and error, I hope. If it proves to be necessary then I'll find a real replacement. \$\endgroup\$
    – zvolk4
    Apr 24, 2020 at 0:50

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