The SW1 diode switching is not correct. Notice that when the switch is in the upper position as shown, D2 and D3 still are in parallel across VR1. Expand SW1 to DPDT, and switch both sides of the diode networks.
Add a resistor from the Q2 drain to source, to assure a rapid and complete turn-off.
There are two "D1"s on the schematic.
Since either R5 or R6 always is in the circuit, you can eliminate one of them and move the other to the left side of SW1 (after C3).
ak