with the amp gain all the way up and filter on 80 and radio to a loud volume that sub should play just fine. you may have an issue with your amp. Get a digital multimeter, set it to ac voltage, get a 50Hz test tone and check the ac voltage output from the speaker outputs from the amp. that will let you know if the amp is producing power. it should be somewhere like 24-28 volts ac for 300w-400w.