Chris, our bass player, has an amazing MusicMan bass from the early 1990s. Over the past year, the input jack has been sounding like a bowl of rice krispies, with lots of crackles and pops. So, I decided to replace it. This turned out to be a bit of a saga, so I thought that it might be helpful to others to share some lessons learned.

The bass has active electronics, which are uniquely switched on, using a special type of 1/4″ jack. Specifically, it is the Switchcraft model 13 jack, which is a mono jack with an isolated make circuit. When you insert a plug into this jack, the plug closes a mechanical switch, which connects the positive side of the battery to the active electronics circuit. This is different to how nearly every other guitar/bass active circuit is turned on. Most other schemes use a stereo jack, with the plug connecting the ground side of the circuit and battery together.

The ErnieBall method allows for a sort of “soft” startup of the circuit, which minimizes circuit noise when you first plugin the bass. That shouldn’t matter in practice, but that is the theory.

Here are a couple of photos of the jack, to show the wiring scheme and what the jack looks like. There is one lug for signal, two (both sides of the switch) for +9V, and one shared ground lug.