I don't think the Ultra has a high level input (straight from an amp speaker output). The High Filter is for eliminating frequencies that are higher than are used by the sub. You should hook it up to the LFE (low frequency effects) output of you amp/receiver, or sub woofer output. Have fun. Dennis
Let me amend by last post. I am actually not sure if the older BASH amp accepted high level inputs, but, I believe the new Sledge amp does, probably from the XLR connectors with the input switch set to "high". As always, check with SVSound to get the correct info. Dennis
Are you loking for high-level (pro audio) line level, or for speaker level inputs? The current PC13 Ultra (Sledge Amp) does not have speaker-level inputs. It can accept line-level balanced (via XLR) or unbalanced (via RCA) connections. The Input Level switch is to select line level input between standard consumer or pro audio voltage levels. it does not allow for the sub to be connected to a receiver's speaker outputs.