I would like to switch between two drains resistors in a high voltage (300 VDC) audio LND150 gain stage. I opted for a BJT instead of a MOSFET, because the MOSFET parasitic capacitance was too high and thus reduced the bandwith of the stage. Here is the idea:
It is basic but it should work.
The problem is the switching transient, it will induce noise at the output of the circuit.
I would like to "soft switch" the BJT to limit switching noise. I thought to ramp on and off the base current of the BJT in about 200 or 300 ms but I don't find how to implement it with discrete components.
Could you suggest a circuit? Or if you have an other idea to switch the drain resistor, keeping in mind that V+ is about 300 VDC?