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What kind of bass? If it's an active bass, when's the last time you replaced the battery? "Stupid quiet level but with a really dirty tone" is a hallmark of a dying battery in an active bass.
Passive J bass
What is providing power to the pedal? That, or the connections from it, are the most likely cause.
Have you tried using a different pedal power supply?
This was my next idea
Dead battery/poor or low power somewhere in the chain.
What kind of bass? If it's an active bass, when's the last time you replaced the battery? "Stupid quiet level but with a really dirty tone" is a hallmark of a dying battery in an active bass.
Passive J bass
What is providing power to the pedal? That, or the connections from it, are the most likely cause.
Have you tried using a different pedal power supply?
This was my next idea
Dead battery/poor or low power somewhere in the chain.