Can FET switching work for all types of 9v effects?

[kimelopidaer]

I wonder about this since
I recall reading on the forum that certain types of switching (FET, Photofet) may work best within a specific range of signal strength.
surpassing a certain voltage could cause unwanted distortion or even bleed through of a supposedly blocked signal.

I wondered how BOSS manages to implement this type of switching system in such a wide variety of effects. Are precautions taken to limit the voltage handled by the switching circuitry?


regards,
K

[amptramp]

If you use a FET switch at a summing junction of an inverting op amp stage, the voltage remains nearly constant, only the current changes.  In real life, you have to allow for capacitances, so a FET right at the summing junction is not always possible, but it is good enough to add a small series resistance with a small feedback capacitor just to stabilize the amplifier for capacitance to ground.  Basically, the FET can be made to approach pinchoff or fully on with a large enough signal.  Most pedals work with signals in the 1 volt range, so FET switching is possible and does not add appreciable distortion.  That's how Boss gets away with it.