Measuring IDSS for a J201 JFET on a daughterboard

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argylehustler

New member
Hi Folks. I've got a few Fairfield Circuitry inspired builds (Chop Shop, Nein) almost done and it's time to get into measuring the JFET's. Coming from a non-engineering background I've pored over any videos on Youtube that remotely mention measuring JFET, IDSS, or both. Many mention measuring typical looking 3 leg transistors.

It seems that if I had a loose J201 like a MMBFJ201 that I could likely pop it on the clip on board that is included on a cheap unit like the FNIRSI LCR-P1 tester. However, I ordered the J201's from stompboxparts pre-soldered to a TO-92 daughterboard. I even got the pin headers recommended by a fellow forum member. However, I realized that I can't just pop that JFET containing daughterboard on the FNIRSI LCR-P1 tester because the bottom of the JFET will not make any contact with that thing and thus won't be measurable. I do realize that D,S,G are labeled on the TO-92 daughterboard so is the answer for achieving IDSS measurement going to involve soldering the pin headers to the TO-92 daughterboard and then inserting it on the tester so it's sort of like a typical 3 leg transistor?
 
I soldered pin headers to mine.
zeropluszero

Post in thread 'zero's various pedal builds'

1000049553.jpg 1000049556.jpg 1000049557.jpg 1000049558.jpg
Desolate Fuzz.
Now, I'm pretty sure it's working, I built 8 of these smd j201s onto adaptors, then male pins and they can then go into the sockets. I them labelled them, and tested them one by one, in all combinations and picked two that seemed to make the right noises and the least bad noise. I don't have a DCA75 to test the 201s better so if you're in Australia and have one and want to loan it to me just send your invoice to my PM haha.
I think I liked the sound in demos, just an absolute blow out noise, not certain that I can get it to work...
 
zeropluszero said:
I soldered pin headers to mine.
zeropluszero

Post in thread 'zero's various pedal builds'

1000049553.jpg 1000049556.jpg 1000049557.jpg 1000049558.jpg
Desolate Fuzz.
Now, I'm pretty sure it's working, I built 8 of these smd j201s onto adaptors, then male pins and they can then go into the sockets. I them labelled them, and tested them one by one, in all combinations and picked two that seemed to make the right noises and the least bad noise. I don't have a DCA75 to test the 201s better so if you're in Australia and have one and want to loan it to me just send your invoice to my PM haha.
I think I liked the sound in demos, just an absolute blow out noise, not certain that I can get it to work...
Click to expand...
Yeah that's what I was thinking. I however don't have the right angle pin headers. I have the straight pin headers. But I think that difference shouldn't matter since those pins can then just sit on a tester like the one I mentioned. Thanks for sharing.
 
Thanks for clarifying. I assume that it doesn’t matter which side of the pin header goes to pcb and which goes to the jfet daughter board? Mine are slightly longer on one side.
 
Careful all pin headers are not the same. I bought some angled male ones off Amazon to solder to my smd j201s and the pins wouldn’t fit into the female sockets I’d already soldered onto the board.
 
bluedmc777 said:
Careful all pin headers are not the same. I bought some angled male ones off Amazon to solder to my smd j201s and the pins wouldn’t fit into the female sockets I’d already soldered onto the board.
Click to expand...
oh this is something i hadn’t considered. So are you are saying that you put pin header sockets on the pcb (male side through pcb, female side facing up towards the enclosure cover), then put the male/male pin headers through the jfet daughter board, and finally you put the daughterboard assembly onto the female socket end on the pcb? Sorry for the obvious question but in seeing the common pcb build view it is not possible for me to see if some part has stuff soldered below it.
 
You lost me at daughter board I must’ve missed that part. I was simply referring to inserting the smd jfet (with headers installed) into the jfet sockets on the pcb. The headers I purchased wouldn’t fit into the sockets. Supposed I could’ve went without using sockets at all but I did with the intention of swapping the jfets.
 
bluedmc777 said:
You lost me at daughter board I must’ve missed that part. I was simply referring to inserting the smd jfet (with headers installed) into the jfet sockets on the pcb. The headers I purchased wouldn’t fit into the sockets. Supposed I could’ve went without using sockets at all but I did with the intention of swapping the jfets.
Click to expand...
Ok your inclusion of sockets in addition to having pin headers makes sense given that you were going to swap the jfets. That's the first mention I've seen of that for jfets. I've definitely socketed for germanium transistors with those little green circle sockets. Is socketing for jfet swaps common?
 
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