The gain knob is used to control how much the volume (output) of the amp increases with each increase in volume on the deck (installed in the dash). This is used to match speakers running of your deck. Other knobs are probably for a crossover (labelled in Hz). This controls what frequencies are passed to the speakers connected to the amp. A Highpass (HPF) crossover passes all frequencies above what the knob is set for. A Lowpass (LPF) pass all frequencies below what the knob is set for. A HPF is typically used when the amp is powering component or full range speakers to keep the ultra low frequencies (anything below 90Hz) from going to theses speakers. A LPF is used when the amp is connected to a sub. Subs dont handle higher frequencies very well.
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The gain knob is used to control how much the volume (output) of the amp increases with each increase in volume on the deck (installed in the dash). This is used to match speakers running of your deck. Other knobs are probably for a crossover (labelled in Hz). This controls what frequencies are passed to the speakers connected to the amp. A Highpass (HPF) crossover passes all frequencies above what the knob is set for. A Lowpass (LPF) pass all frequencies below what the knob is set for. A HPF is typically used when the amp is powering component or full range speakers to keep the ultra low frequencies (anything below 90Hz) from going to theses speakers. A LPF is used when the amp is connected to a sub. Subs dont handle higher frequencies very well.