We have a friend of the company and 30+ year bass player who offered this piece of advise almost 20 years ago. I happened to stumble across his note in an email the other day (sent before he was famous).
His suggestions address a common problem scenario created when your bass player wants to use the line output on the amp (as opposed to a direct box (DI)) to connect to the sound system. This can apply to guitar players, too.
Dave, the bass player should plug the instrument directly into the DI. From the DI, take one out to the snake and the other to the bass amp. The bass amp is for the bass player's tone and volume on stage. If the DI has a ground switch, flip it.
Using the direct line output of the amp to the snake opens the sound system to the grounding of the audio mixer, amps, lights, and regular AC, and you'll almost certainly hear hum related to the ground unless you have common and/or isolated grounds.
Remember that sound engineers would rather have (and need) full control of the bass volume and tone. Bass amps are good for stage volume and tone but don't fair well as pre-amps in real systems.
What sounds good on stage doesn't necessarily sound so good in a system that can hit better SPL and distances.
Editor's Note: We'd also suggest a Morley HumX in order to isolate the electrical ground on the bass amp without defeating the safety ground with a commonly used 3-prong to 2-prong adapter.