A number of years ago I built a 142.5L subwoofer with a down-firing 12" Shiva driver, a 15" front passive radiator, and an AVA250 plate amplifier. It has served me well and sounds great! Last week the AVA250 started buzzing. It has an auto-on circuit that when it detects a signal the amp turns on and when my Denon receiver is turned off the AVA250 is supposed to return to the off sleep mode. It's not doing that now. I have looked online for a schematic for the AVA250 with no luck. Anyone here on the forum have a schematic or know where I can get one? Also, my 12" Shiva has bottomed out too many times and is starting to bang when hitting bottom. Any suggestions on which subwoofer driver I should replace it with considering it is in a 142.5L box with a 15" radiator? Thanks.