Everything You Wanted to Know About JFETs (but Were Afraid to Ask)

Oh, man... I spent the last few days trying to decipher the Rod Elliot "designing with JFETs" piece and now this!

I feel like a blind man trying to put a puzzle together with work gloves on 🤣
 
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See, what I come to expect from Chuck when I see a title like "Everything You Wanted to Know About JFETs (but Were Afraid to Ask)" is Chuck to write a very clear and concise explainer written in simple language that my limited intelligence can parse.

Not a link to a BOOK fergodssake! What do you expect me to do, read it???
 
bifurcation said:
...a BOOK fergodssake! What do you expect me to do, read it???
Click to expand...

Yes, the same way you would read an encyclopedia. You look up what you need, not read it cover to cover. The best parts are some of the application circuits in section 6. Check out the phase shifter at the top of page 6-33. Replace the 1M pots with optos. Reminiscent of the UniVibe, only with JFET stages it takes fewer parts. Or maybe the preamp circuit at the bottom of page 6-36 could be adapted to pedal use.
 
Chuck D. Bones said:
Yes, the same way you would read an encyclopedia. You look up what you need, not read it cover to cover. The best parts are some of the application circuits in section 6. Check out the phase shifter at the top of page 6-33. Replace the 1M pots with optos. Reminiscent of the UniVibe, only with JFET stages it takes fewer parts. Or maybe the preamp circuit at the bottom of page 6-36 could be adapted to pedal use.
Click to expand...
The sample circuits are awesome. I always knew them as the AN-32 document.
 
Chuck D. Bones said:
Yes, the same way you would read an encyclopedia. You look up what you need, not read it cover to cover. The best parts are some of the application circuits in section 6. Check out the phase shifter at the top of page 6-33. Replace the 1M pots with optos. Reminiscent of the UniVibe, only with JFET stages it takes fewer parts. Or maybe the preamp circuit at the bottom of page 6-36 could be adapted to pedal use.
Click to expand...
Hey Chuck, is there any particular reason for the different source and drain resistors in the two stages of the phase shifter? I'm willing to give it a try when I find the time
 
Thanks, this is super-useful. They (JFETs and their relatives) are quite quirky beasts, I have found. I’m not sure I understand entirely how they work their magic, but if I don’t after this …
 
lrgaraujo said:
Hey Chuck, is there any particular reason for the different source and drain resistors in the two stages of the phase shifter? I'm willing to give it a try when I find the time
Click to expand...
I think it's because of two things: 1) the stages are DC-coupled, 2) the gate and source are not at the same DC voltage. That means the bias is different for every stage. Add more stages and you run out of headroom. The right way to do it is AC-couple the stages like Mieda-san did with the UniVibe.
 
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