Voltage Fluctuation in JFETS

[vanhansen]

In a multi-JFET circuit, such as the ROG Thunderchief or the BSIAB, is it normal for the drain voltage to fluctuate while signal is going through the circuit?

I'm curious because in adding a second stage to my Marsha Valve circuit, I notice the 2nd FET drain voltage go up to a little over 5 volts from 4.5v when signal is going through it.  On the gate I have a 1M pot and a 1M resistor to ground.  The 1st JFET stays pretty steady.  Once the signal stops, the voltage drops back down to 4.5v.  The signal is just my guitar being strummed.

[ragtime8922]

If you hook up your volt meter from drain to gnd and then start playing, the reading will, and should, go crazy.  Then when you stop playing in will go close to bias but if you still have the guitar volume knob up and the circuit in the on position you may get a tad bit of flucuation.

[vanhansen]

If you hook up your volt meter from drain to gnd and then start playing, the reading will, and should, go crazy.  Then when you stop playing in will go close to bias but if you still have the guitar volume knob up and the circuit in the on position you may get a tad bit of flucuation.

That's exactly what I'm seeing.  I've learned that having the meter hooked up while playing sure makes things easier.  It starts at 4.5v, goes nuts to a little over 5volts when I start playing, then settles down when I stop playing.

Thanks.