fetzer valve

[rtill]

Hello again...built this circuit figure 1 on.... http://runoffgroove.com/fetzervalve.html as more of a boost.. wondering why I get a farting sound when I play - volume control works but it doesn't get very loud.. I've adjusted the trimpot and still get the same results.  Using a j201 n channel jfet.   Any ideas of what's going on?

[stm]

The circuit you describe will clip whenever the guitar exceeds +/- 0.4 V approximately, thus what you are hearing is normal.

If you want a clean boost with its own valve-like coloration then go for a Fetzer Valve Deluxe and:

a. Use a 2N5457, 2N5458 or MPF102 FET instead of a J201
b. Use 18V instead of 9V to have plenty of gain and output headroom
c. Use the suggested presence capacitor, a similar value, or remove it, but no giant source bypass capacitor
d. Choose Rs and tune the drain voltage according to the Fetzer Valve online calculator available at ROG's site

Also, for more info check here:

http://www.diystompboxes.com/smfforum/index.php?topic=46345

[petemoore]

wondering why I get a farting sound when I play
  quite likely the transistor is not biased within operating parameters.
  check out the debugging thread, post voltages....or just go through the board w/DMM to find 'it'.