Hi-Lo Level Converters

Hi-lo level converter buying guide 2026

A hi-lo level converter, also called a line output converter or LOC, turns amplified speaker level signal into low level RCA signal that an aftermarket amplifier can accept. It is the component that lets you add an amplifier or subwoofer to a factory stereo that has no preamp outputs, which describes the overwhelming majority of cars on UK roads in 2026.

When you need one

If you are keeping your original head unit, whether that is a simple radio or a large integrated infotainment screen, you almost certainly need a converter. Factory systems rarely expose RCA outputs, and tapping speaker wires directly into an amplifier input risks damaging the amp and introduces noise. A converter handles the level matching and grounding properly.

Passive or active converters

• Passive converters. Use a transformer or resistor network, need no power feed and suit modest signal levels. Simple, cheap and effective.
• Active converters. Powered units with adjustable gain and far better noise rejection, ideal for high output factory amplifiers.
• Two channel units. The standard choice for adding a single subwoofer amplifier to a factory system.
• Four and six channel units. Required when you are amplifying front and rear stages as well as bass.
• Summing converters. Recombine a factory system that has already split the signal across separate frequency bands.

Signal sensing and remote turn on

Factory head units have no remote turn on wire, so your amplifier needs another way to know the ignition is live. Most quality converters include DC offset or signal sense circuitry that generates a 12 volt remote output automatically when audio appears. Check the specification before you buy, because retrofitting a switched live afterwards means dismantling trim you have already refitted.

Dealing with factory equalisation

• Premium factory systems. Bose, Harman Kardon and Burmester systems often apply heavy equalisation, so a DSP based converter gives a flatter result.
• Rolled off bass. Many OEM units reduce low frequencies as volume rises. A processor with a flattening function restores them.
• Time alignment. Factory delay applied per speaker can confuse a simple converter. Sum channels carefully or use a dedicated interface.
• Load resistance. Some head units mute if they do not see a speaker load, which certain converters emulate internally.

Brand quality at a glance

• Connects2. Broad UK vehicle coverage with well documented, vehicle specific interfaces.
• PAC Audio. American specialists in OEM integration, particularly strong on signal sensing and load emulation.
• Audison. Prima and bit series processors offering full DSP correction of factory equalisation.
• Helix. German DSP amplifiers with automatic factory signal analysis built in.
• Stinger and Scosche. Dependable passive and active converters at sensible money.
• AudioControl. Excellent active converters with generous input voltage handling.

Compatibility and fitting

• Fascia adapter. Fills the gap around a new head unit so the dashboard looks factory finished.
• ISO harness. Lets you connect to the vehicle loom without cutting a single original wire.
• Steering wheel control adapter. Retains your volume, track and phone buttons on the wheel after an upgrade.
• Aerial adapter. Converts the vehicle antenna plug to the standard connector your new equipment expects.

Avoiding noise and alternator whine

Most noise complaints trace back to grounding rather than to the converter itself. Ground the amplifier to bare chassis metal within about 45cm, keep RCA cable on the opposite side of the car to the power cable, and set gains with the head unit at roughly three quarters volume rather than maximum. Where a factory head unit is genuinely noisy, an active converter with a differential input will usually solve it.

Why buy from Bass Junkies

Bass Junkies has been integrating aftermarket amplifiers with factory systems since 1995, long before infotainment screens made the job complicated. We can tell you which converter suits your specific vehicle and whether a DSP is the better answer. Our Wolverhampton workshop handles OEM integration every week, and technical advice is free on 01902 863 005.