OK I looked up your amp specs and manual. If you have the BASS Boost switch turned on the turn it off and try the control. If the switch is off turn it on and try the control.
If the bass boost control does not change anything after trying this experiment the you got the worng bass knob or it is broken.
My feeling is that you have the bass boost switch on and you are already getting the full boost from the amp, hence bypassing the functionality of the knob.
At 157.2 DB no one will hear you scream
