Bottomline up front (BLUF) : Plug the P Bass into the HIGH

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Your Fender PBass should around 10K ohms (unless you’ve added active pickups or done other PUP mods) , as are most passive electric bases and guitars. This is considered “high” output impedance: between 6K to 10+ K ohms for passive PUP configurations as opposed to say stomp box that has around 100 ohms output or “low” impedance output.

You want to plug high impedance outputs into much HIGHER impedance inputs. 10X or more is a good ROT (rule of thumb) and most all guitar and bass amps have at least ONE 100K to 1M ohm “high” impedance inputs – they may also have “low” inputs but you don’t want to use that for guitar or bass.

You are NOT trying to impedance match in these cases (unlike other audio situations) because if you put a 10K ohm Z (Z=impedance) guitar/bass into a 10K ohm input Z it will simply load down the passive pickups and severely impact signal and high freq’s.

Larry