Re: An Orange Tiny Terror preamp in a (stomp)box

Posted by Frank_NH on Sep 18, 2015; 2:46pm
URL: http://guitar-fx-layouts.238.s1.nabble.com/An-Orange-Tiny-Terror-preamp-in-a-stomp-box-tp24339p24494.html

Interesting project!  I think you look at the Runoff groove amp-in-a-box design for some tips on how to convert the Orange preamp to a stompbox.  Some of my thoughts:

* You may not want to remove all the cathode bypass caps as they greatly affect the gain (usually a factor of 2 or more).  My experience with a similar circuit is that it is best to lower or remove the first one, C1 in this case, but keep the others as is.  Too much gain on the first JFET stage gives you distorted bass frequencies which sound "farty" to me.

* You definitely want trimmers to bias the JFETs given the wide variation in Idss and Vp.  However, don't make them all 100K - lower is better (50K is what I normally use, sometimes smaller yet depending on the JFET).

* I like the dual gang Gain control in this design.  That's one of the things that makes it unique versus other amp sims.

* As far as source resistor values are concerned, you can probably keep them as they are for the real amp, especially if you have a source bypass cap.  I wouldn't necessarily use the Fetzer source resistor values since they depend entirely on your specific JFET's operating characteristics.  On the other hand, an optimal source resistor for any application will likewise depend on the specific JFET.  Maybe the approach should be this:  if you want to use JFETs in an amp sim, you should sort through your stash and select JFETs that will be the most "tube like" in terms of response and gain, rather than trying to make a design which can accommodate any old JFET.