Tonal and gain differences between various jfets?

[grolschie]

Hi there,

I have googled somewhat and searched this forum, but I cannot seem to find a definitive comparison of various jfets in terms helpful to a n00b pedal builder like me. I have built a ROG "Eighteen" from OLC and wish to try different jfets but not sure how they all compare in terms of gain, terms of smoothness, or whether they can be all simply substituted even?

I have tried the stock J201s and then swapped to MPF102s. I noticed the gain dropped a heap with the MPF102s, mega difficult to bias, and when one was in Q2 there was almost no ouput.

Would I be correct in guessing that Q1 would be affected the most by jfet substitution?

Any chance of someone please giving me a rundown on various jfet options in terms of gain and smoothness?

Another n00b question:  does quality control in manufacturing, manufacturer, etc affect things?

Many thanks in advance.
grol

[Gilles C]

You can get a good explaination about FETs specs there http://runoffgroove.com/fetzervalve.html

Gilles

[grolschie]

You can get a good explaination about FETs specs there http://runoffgroove.com/fetzervalve.html

Gilles

Excellent. Thanks for that. So that covers gain levels. What about smoothness/harshness? I remember trying different OPAMPs in my Rat pedal and finding differences even though gain were similar. I am wondering if the same applies to JFETs? Cheers.