jhergonz wrote:indyguitarist wrote:
You're going to have to sort through jfets. Also, layout is critical for noise.
Hi! Iknow this thread is years ago ... but I'm really curious about this one. I'am electronics literate so please help me out. when you say "Sort" the JFETs, how exactly do I need to sort the Jfets? I really want to learn, please guide me. Thank you in advance.
As I understand it: The J201 (and 2N5457s and similar JFETs) tend to have widely varying specs, so each JFET might/will require different bias resistors (specifically the drain in this case) to get the 5v or whatever voltage is required for the pedal to sound good/how Brian intended it. In the Velvet fuzz, the JFET drain resistor is 15k but using a random J201 will probably not give 5v (or whatever) and may also sound terrible. You could use a trimmer (e.g. 20-50k) to get the required voltage out of most parts straight out of the bag, but if it's a good distance away from 15k it may not sound too much like the og pedal. What it boils down to is either:
a) Use a trimmer on each JFET
b) buy a large quantity of JFETs, then plug them into the circuit and until you find three close to 4.5-5v with a 15k resistor
c) same as b), but find three that will bias with a standard value resistor close to 15k, (8k2/10k/12/15/18) <-
what i did.Since through-hole JFETs are going obsolete (J201, 2N5457 at least) and becoming increasingly expensive, if not actually particularly rare, for option b) and c) you may need to look into using surface mount (smd) jfets and adaptor boards, although I see that tayda are still selling through-hole for cheap enough to buy a handful to try out (though the smd are way cheaper):
https://www.taydaelectronics.com/catalo ... lt/?q=j201Whatever you end up doing, if you haven't already bought a small breadboard, a pair of jack sockets and a bypass switch to try it out circuits, get it now.
There's a thread about the plexi drive and biasing here, and diystompboxes is generally a good source of information, if a little tricky to search (i find google searches for pedal related stuff often directs there anyway):
https://www.diystompboxes.com/smfforum/ ... c=115814.0