JFET Buffer help

[Ben Lyman]

I learned awhile back to protect my JFET OD pedal with a 33k series resistor on the input to the gate.
How about this AMZ JFET buffer? any need to protect it?
And if so, can I expect a slight volume drop at the output?

[antonis]

Your output isn't dominated by anything before Source, so it's impedance can't alter due to input resistane..

Also, any reasonably low resistance (compared to G-S resistance) can't affect FET input impedance because of Gate - Source zero current..
(your input impedance is heavily depended on your specific FET g_m and R_Source // whatever it drives..

Tone alter is another matter and it depends on source input resistance and input cap values also with series resistance place & value..

[Gus]

A link that might help
http://www.edn.com/electronics-blogs/living-analog/4390990/Emitter-Followers-as-Colpitts-Oscillators-

You can find more information using searches like  "emitter follower stability" "follower stability"  "opamp stability"

[bool]

You can "protect" jfets similar to a mosfet: with a small zener across G-S. But beware the polarity - compared to a mosfet, swap the zener A and K (reverse them). 8 or 9V rating should be fine. But the small zeners add circa 50pF capacitance, so you should also factor that ...

[anotherjim]

Between R1 and Q1 you can add a series protection resistor that avoids forming a divider with R1, but you do also see them before R1 - against 1M, 33k drops a trivial amount.
If I was paranoid about high input voltage damage, a pair of reverse protection diodes is what I'd suggest. Must be a series resistor and the diodes go between that and the gate.

Same idea as these protection diodes. You can also protect an output this way, so long as there's a series resistor between the output jack and the diodes.

[Ben Lyman]

Thanks guys, a lot of your technical jargon sorta went over my head but I took some of it in.
This is how I did it in my OD pedal so I think I'm gonna try it like this in my buffer too:

What's the worst that could happen anyway? I might have to unplug my buffer to finish the set and go home and make a new one, right?

[R.G.]

But wouldn't it be neat if you never had to unplug it because it was hosed?   

At the risk of starting an off-topic discussion, why a bare JFET buffer? There are issues...

[Ben Lyman]

At the risk of starting an off-topic discussion, why a bare JFET buffer? There are issues...

I don't mind going off topic at all.. ever.. it's my specialty!
So please tell me more. I just liked the way it sounded when I bread boarded it and it came from AMZ so I thought it would be a good choice. I didn't like the TL072 "Klon" buffer that I made, it just sounded sterile and too bright or something.
Also, I have a bunch of JFETs that didn't work out perfectly for OD's or phasers.