need clamping & clipping circuit help to keep steady 30v
 

Have not worked in detail with electronics for a while. I have a bad
signal spike distortion for a very brief time of 50us on a control line
held at 30v dc. It spikes up to 45 and down to -10 before stabilizing
to 30v again. What would I need as a line clamp or conditioner to it
swinging so dramatically? I could probably live with 5v swing one way
or another. Any suggestions?