Four jumpers A, B, C and D provide adjustable tone control for bass and treble through jumper caps. Key benefits Finegrained bass control: A defines the lower limit and B defines the upper limit of the bass range, allowing you to tailor bass response to your system. Distortion management: If the bass sounds distorted when set , you can adjust by changing the jumper caps to limit the very low bass. Flexible bass tuning: Removing the cap on Jumper B increases bass, while having the cap on Jumper B reduces bass. frequency shaping: Jumpers C and D control the frequency range; when their caps light up, the treble becomes the loudest. Clear, straightforward operation: Visual indicator with cap lighting helps you identify when treble is at its peak and adjust accordingly. How it works Bass control Jumpers A and B set the bass range. A is the lower limit, B the upper limit. If distortion occurs from excessive bass, remove the jumper cap from bridge A to limit the superlow bass and reduce distortion. For bass adjustment within the range, remove Jumper B's cap to increase bass; install Jumper B's cap to reduce bass. Treble control Jumpers C and D control the frequency range. When the caps on Jumpers C and D light up, the treble is at its loudest. Use scenarios Scenario 1: Small bookshelf speakers that distort with heavy bass. Use Jumper A to limit the superlow bass and reduce distortion. Scenario 2: Music that benefits from deeper bass warmth. Remove Jumper B's cap to boost bass, then restore cap to reduce bass as needed. Scenario 3: Home theater or brightroom listening where treble needs tuning. Enable the caps on Jumpers C and D to raise treble to the desired level. Notes This module uses four jumpers (A, B, C, D) and their caps to adjust bass and treble responses. Caps lighting on Jumpers C and D indicates the treble is at its peak.