Active system adapters are used to maintain factory-installed sound systems. This allows the connection of aftermarket radios to a vehicle's active system while retaining the OEM amplifier and connected speakers by adapting, adjusting, or converting the output signals from the signal source to the signal input of the OEM amplifier. Depending on the vehicle and the installed OEM active system, various functions such as fader or sound and subwoofer settings may be omitted. In some cases, depending on the OEM system and the aftermarket radio, increased noise or a turn-on or turn-off sound may occur.