Re: A few definitions _ Overdrive, Boost, Fuzz, Distortion

Posted by Frank_NH on Oct 11, 2014; 11:46pm
URL: http://guitar-fx-layouts.238.s1.nabble.com/A-few-definitions-Overdrive-Boost-Fuzz-Distortion-tp13960p14231.html

Someone called??

I also had hiss when I attempted the vero version.  I think part of the problem may be in the layout, but I can't be sure.  Having said that, I would move that 100 uF cap away from Q2, perhaps under the cut in column 13.

As for biasing, I did a calculation for you in my spreadsheet (here's an image):



I used 201 JFET data for Vp ~ -0.91 V and Idss ~ 0.64 V.  For Vdrain = 4.5 V, I get a drain resistor value of 15K.  Now your trimmer is only 20K, so you don't have much wiggle room.  In fact if your JFET's Vp is much lower than -0.8V, you probably can't bias the JFET!   So, two things you can try:

(1) change the trimmer to 50K, or
(2) use a JFET with a Vp ~ -0.9V or more (using your handy dandy JFET Tester to find the magic JFET ).

You can also try a 2N5457 instead of the J201, but it won't have the same gain.

Hope you can get the problems sorted.  Let us know how it goes - and start a new topic as I'm sure there will be a lot of interest in this...