A line output converter (LOC) translates a speaker-level signal from an amplifier or head unit into a line-level signal suitable for driving the inputs of an aftermarket amplifier. It is most commonly used when a factory head unit is being retained and an aftermarket amplifier is being added — the factory unit has no preamp outputs, so the LOC provides the necessary signal conversion.
The LOC connects to the speaker output wires of the factory head unit or factory amplifier. These wires carry a relatively high-voltage signal (several volts at normal listening volume) compared to the millivolt-level signal on a preamp output. The LOC’s internal circuitry attenuates this signal to the correct level for an amplifier’s RCA inputs and presents it through standard RCA connectors.
Selecting the correct connection point for the LOC matters. Tapping into the speaker wires at the head unit gives the cleanest signal before it reaches any speakers, which may have long cable runs with potential for interference. Tapping near the speakers themselves is sometimes more convenient but carries a greater risk of picking up interference.
LOC installation involves identifying the correct speaker output wires, which can be confirmed with a multimeter or by consulting a vehicle-specific wiring diagram. The LOC’s input leads are connected to these wires using appropriate splice connectors. The LOC then requires a chassis ground connection and, on units with remote turn-on output, a connection to the amplifier’s remote input terminal.
Many LOCs include a signal-sensing turn-on feature. When audio signal is present, the converter activates and sends a 12 V trigger to the amplifier’s remote input, eliminating the need to run a separate remote turn-on wire from the head unit. Setting the LOC’s input sensitivity correctly — by adjusting its trim pot while playing audio and monitoring the output level — is essential to achieving a clean signal without clipping at the converter’s input stage.