Same here with my HPF. For some reason, at our practice space I get a really boomy low A that really bothers me. One of the guitarists said the same thing for himself after I mentioned it. The past two practices I've had the HPF set to about 80 as well and it really cleans up that boom.
Did you had the Broughton Resonant Filter Equalizer or do I remember incorrectly?
Somebody here had that.