Structo wrote:Say what was the deal with biasing the JFET on this board?
Was it the 8K2 resistor that needs to be adjusted for the bias?
Anybody remember how that works or what the proper voltage is there?
The trimmer is for input gain right?
You can leave the 8k2 resistor as it is, and change the source resistor instead.
Measure the drain voltage on the 10k resistor, and the voltages on the 150k.
The drain should be 1/2 of the 150k voltages. And the source voltages 2,5-2,6 volt.
I use 4,7k-5,6k on the source. Seem to work fine.
I read around 12 volt on the 150k, 6,3 on the drain, and 2,6 on the source. The sound is similar to the normal channel, but you can set the level much higher on the trimmer to make the fet work like a clean boost, or to add more gain to the od channel. Pretty much like the PAB work. but then you can find the breakup spot on the fet, work with different resistors until you find the sound you like. You can add trimpots instad of resistors, and measure them when you have dialed in your sound. Then find the resistor closest to your measured ohm and solder them in where the trimpot was.
You can find different combinations that you like. Write them down, so you know what to put in there the next time you need a tweek, or in another build. There will be some differences between builds, cause the b+5 also change in from amp to amp.
Frank.
