It's been a while in the making, but I finally completed my Dumble clone, also know as the ROG Umble. If you want to know still more, Google is your friend. All the info can be found in the link, but in short it is a stompbox adaptation of a preamp section of that illustrous amp and replace the different tubes by JFET transistors.
For ultimate performance these jfets, like the tubes in an amp, should be biased at half PS voltage to provide optimum swing up and down the spectrum. So tired of working with trimpots, I set up 4 bias pots next to the 5 control pots on my breadboard during testing.
What you see in the vid is my trying to get the transistors at exactly 4.5V. It took me a long time to realize that I shouldn't be biasing the circuit at maximum gain, that' a little too much.
As this circuit has gain galore, I opted to put 2N5457 (less gain) in Q1. Other fets are still J201. This makes the circuit a bit more stable.
