Re: ROG Supreaux

Posted by Frank_NH on Aug 22, 2014; 2:40pm
URL: http://guitar-fx-layouts.238.s1.nabble.com/ROG-Supreaux-tp12551p12562.html

Nice layouts - thanks!  I may build this, though I've had mixed success with jfet-based circuits - some seem to bias OK and sound good others not, though the trimmers help.

Here's an idea that I had (certainly not novel) for replacing the trimmers, since I never seem to have the right trimmer values and I've noticed that they can be noisy.  For a biasing situation where you simply need to find the correct resistance for a given jfet, I would consider replacing the trimmers with sockets for ordinary resistors.  When it comes time to bias, just select a resistor which gets your the proper bias voltage at the drains of the jfets.  You can do this by trial and error - start with a value half of what the trim pot would be (50K in this case) then dial it in by replacing the resistors with values which get you close enough to bias voltage.  You could even take a couple of 100K pots and wire them to your sockets, dial in the bias, measure the resistance, then install the appropriate resistor in the socket.  Note that since you are using a socket, if you ever decide to change the jfet, you can rebias with using a different resistor.