Quick answer
Distortion that gets worse when you turn it up is most often gain set too high or the amp starving for power. Turn gain down using a safe setup method and check ground and power wire gauge.
Problem
- Harsh, clipped, or distorted sound when you turn it up.
Symptoms
- Harsh buzz above moderate volume.
- Bass flattens suddenly - may smell hot voice coil.
- LED on amp blinks under load.
Cause
- Gain too high vs headunit pre-out voltage.
- Undervoltage at amp on idle with big draws.
- Driver mechanically bottoming from mis-tuned crossover.
Fix Step-by-step
- Lower amp gain to minimum; set headunit volume to a sane test level; bring gain up per safe method in our gain guide.
- Verify ground integrity and conductor gauge for the amplifier current draw.
- Swap L/R channels to see if distortion follows speaker or upstream path.
Notes
Related: Setting amplifier gains.