Major pop in my switching mod, help.

[Tubis]

I´m switching between to gainpots with optocouplers. In the first picture you can se that i just placed two optocuplers to block backwards interaction.

In the second picture you can se how i did the switching in the Marshall SL-X.

I stole some current to the optos and put to mosfets to drive theme.
When the footswitch is opened the voltage to the first mosfet opens it and turns that opto on.
When the footswitch is closed the voltage to the first mosfet turns zero and the voltage to the other mosfet rises and opens that and that opto.
The problem is that when the switching that accurs when the footswitch opens make a realy loud pop, a realy loud.
The switching that occurs whene the footswitch closes is dead silent.
What is creating this pop and how can i stop it?
The switching at the same time switches two mastervolume witch the IC M5201 that is there original.
I did this switcihg before but with optos as masterswitches and that was dead silent.
Please help.

[Tubis]

When i turn off the gainpot that is being dissabled when the switching pop occurs there is no pop. So it must be signal oriented. But why no pop when switching in both directions?

[Tubis]

Well it seems that the mother fucking Marshall ship dont like to switch when the signal levels are different. Tomorrow the garbage goes and a couple of vactrols goes in.

[loudthud]

Just a guess but maybe in one direction both opto's are on at the same time breifly which is ok but in the other both are off. When both are off there is no path to ground for the grid and it floats up but when one of the opto's turns on it creates the pop. Try adding a 1meg resistor to ground at the 2nd tube's grid.

[Tubis]

Just a guess but maybe in one direction both opto's are on at the same time breifly which is ok but in the other both are off. When both are off there is no path to ground for the grid and it floats up but when one of the opto's turns on it creates the pop. Try adding a 1meg resistor to ground at the 2nd tube's grid.

No, not the problem. I switched only the optos with the master volume fixed to one of theme not using the marshall chip and no pop att all. The optoswitching works fine. It´s the marshall chip that pops like hell.