Kenwood 2-Channel Amplifier (KAC-729S) Ground Isolation Circuit: This circuit cancels noise from the input of the negative side of the RCA cable, preventing vehicle electrical noise from interfering with the music. Quiet Turn-On: This feature allows the amplifier to power up over a period of several milliseconds instead of instantaneously, protecting your speakers from thumps and other sounds that could be damaging. Internal Crossover: The internal crossover is a 12dB/octave, 80Hz low-pass crossover. The crossover may be turned on for low-pass operation, or the crossover can be turned off for full-range output.