Key takeaways
- Use the correct input type: connect high-level inputs to speaker wiring unless the manufacturer specifically permits another method.
- Match the signal range: a converter that clips at the factory amplifier’s maximum output will sound harsh even if its RCA output level is adjustable.
- Keep gains conservative: the LOC gain and amplifier gain should not both be used as volume controls.
- Check channel content: a tweeter or center-channel output may contain little bass and is a poor subwoofer source.
- Avoid unnecessary summing: combining channels can fix a missing frequency range, but incorrect polarity or timing can cause cancellations.
For most factory car audio upgrades, the best line output converters for car stereo systems are the AudioControl LC2i Pro for a simple subwoofer installation, the AudioControl LC7i for adding several amplifier channels, and the Wāvtech linkDQ when signal quality, factory integration, and adjustment flexibility matter more than the lowest price.
Quick comparison
| Model | Output channels | Best use | Notable signal/load capability | Remote turn-on and controls | Approximate market range |
|---|---|---|---|---|---|
| AudioControl LC2i Pro | 2 | Factory radio to subwoofer amplifier | High-voltage speaker-level input; AccuBASS restores bass that is reduced at higher volume | GTO signal-sensing turn-on; independent output level and bass restoration controls | $130–$180 |
| AudioControl LC7i | 6 | Factory system to front, rear, and subwoofer amplifiers | Accepts multiple factory channels and sums or distributes them for a multi-amplifier system | Signal-sensing turn-on; channel-level and AccuBASS adjustment | $220–$300 |
| Wāvtech linkDQ | 6 | Factory integration with sound shaping and multiple amplifiers | High-level inputs, differential circuitry, selectable signal routing, and DSP-style equalization functions | Signal-sensing turn-on with configurable behavior; output level, delay, and filter controls | $280–$400 |
| PAC LP7-2 | 2 | Budget subwoofer or two-channel amplifier installation | Speaker-level to RCA conversion with load-tolerant factory integration | Automatic turn-on; output level adjustment | $50–$90 |
| KICKER KISLOC2 | 2 | Compact, uncomplicated amplifier add-on | Two-channel conversion and built-in signal sensing in a small module | Automatic turn-on; basic gain adjustment | $40–$70 |
Prices are typical market ranges rather than fixed prices. Features and packaging can change by production year, so confirm the current installation manual before ordering.
Which converter fits your installation?
| Your situation | Best direction | Why |
|---|---|---|
| Adding one subwoofer amplifier to a standard factory radio | Two-channel LOC such as LC2i Pro, PAC LP7-2, or KISLOC2 | You need left and right bass signal, not six channels of processing. |
| Adding front, rear, and subwoofer amplifiers | Six-channel LOC such as LC7i or linkDQ | It preserves useful factory channels and avoids buying several small converters. |
| Factory bass becomes quieter as the volume rises | LC2i Pro or LC7i | AccuBASS can compensate for common factory bass roll-off, when adjusted correctly. |
| Factory system has separate amplified channels or active crossovers | Advanced six-channel LOC or DSP-based interface | A basic two-channel converter may miss a full-range signal or produce poor staging. |
| Very little space behind the dash or seat | Compact two-channel unit | Smaller wiring and fewer controls simplify mounting, but you give up routing flexibility. |
| Factory amplifier remains in use | High-level-input LOC designed for OEM loads | It should accept speaker-level voltage without overloading or altering the factory amplifier. |
Best overall for a subwoofer upgrade: AudioControl LC2i Pro
The LC2i Pro is a strong choice when the factory radio stays in place and the main goal is adding a subwoofer amplifier. Its two-channel design keeps the installation focused: connect the left and right factory speaker outputs, adjust the RCA output, and send the signal to the subwoofer amplifier.
Its main advantage over a very basic LOC is AccuBASS. Many original-equipment radios reduce bass at higher volume to protect small factory speakers. If the converter receives that reduced signal, the aftermarket subwoofer may become less impressive exactly when you turn the system up. AccuBASS is intended to restore part of that lost bass curve. It must be adjusted gradually; too much correction can sound boomy and can force the amplifier or subwoofer to work harder than necessary.
The LC2i Pro also has a dedicated remote output, so the amplifier does not need a separate switched wire in many vehicles. That convenience is valuable, but verify that the signal-sensing mode actually shuts down after the vehicle powers off. Some factory systems remain active for several minutes.
Best for multiple amplifiers: AudioControl LC7i
The LC7i is better suited to a complete factory-radio upgrade with separate front, rear, and subwoofer amplification. Six output channels allow a cleaner system layout than splitting a single pair of RCA outputs repeatedly. It can also help when the factory audio system provides different frequency ranges on different speaker channels.
Choose it when you need channel count more than absolute simplicity. A six-channel LOC requires more diagnostic work: you must identify which factory speakers carry full-range information, whether the signal is already filtered, and whether left/right channels are balanced. If your vehicle provides only a full-range front signal and the rear outputs are heavily filtered, the LC7i cannot manufacture missing musical information. It can route and shape what it receives, but it is not a replacement for a vehicle-specific DSP interface.
Best advanced option: Wāvtech linkDQ
The linkDQ targets installations where the converter needs to do more than change speaker-level voltage into RCA-level voltage. Its multi-channel architecture, signal routing, filtering, and adjustment options make it useful with complicated factory systems and several amplifiers.
This extra flexibility is worthwhile when you need to correct level differences, create a subwoofer feed from available channels, or manage a factory amplifier that does not provide a convenient full-range output. It also introduces more setup variables. Plan to use a test track, a digital multimeter or oscilloscope where appropriate, and the manufacturer’s gain-setting procedure rather than turning every control clockwise.
Best compact budget choices
PAC LP7-2
The LP7-2 is a practical two-channel choice for a conventional subwoofer amplifier installation. It is suited to buyers who need speaker-level input, automatic turn-on, and basic output adjustment without paying for bass restoration or multi-channel routing. It makes the most sense when the factory radio delivers a stable full-range signal and does not aggressively change its equalization with volume.
KICKER KISLOC2
The KISLOC2 is useful where physical space and cost matter. Its small two-channel format can fit behind trim panels that will not accommodate a larger processor. It is a sensible match for a modest amplifier upgrade, but it has fewer tools for dealing with factory bass roll-off, separate factory crossovers, or complex signal summing.
Signal quality: what matters beyond the advertised voltage
A LOC does not automatically improve sound quality. The important questions are whether it accepts the vehicle’s speaker-level voltage, maintains a clean signal under the factory amplifier’s load, and avoids adding audible noise. Differential factory outputs require a compatible input stage; grounding a speaker negative wire can damage some OEM amplifiers.
- Use the correct input type: connect high-level inputs to speaker wiring unless the manufacturer specifically permits another method.
- Match the signal range: a converter that clips at the factory amplifier’s maximum output will sound harsh even if its RCA output level is adjustable.
- Keep gains conservative: the LOC gain and amplifier gain should not both be used as volume controls.
- Check channel content: a tweeter or center-channel output may contain little bass and is a poor subwoofer source.
- Avoid unnecessary summing: combining channels can fix a missing frequency range, but incorrect polarity or timing can cause cancellations.
Remote turn-on behavior and installation fit
Signal-sensing turn-on is convenient, but it is not identical across vehicles. Some converters detect audio immediately; others wait for a minimum signal level. A factory system may also produce brief startup tones, delayed shutdown, or low-level audio that keeps the amplifier awake. If the amplifier remains on and drains the battery, use a proper switched source or a converter with a configurable turn-on mode.
Allow room for connectors and service access. A module measuring roughly 4 to 7 inches long may need 1 to 2 inches of additional clearance for wiring bends. Mount it securely away from water, HVAC condensation, seat tracks, and high-current power cables. Do not leave it loose inside the dash, where vibration can create intermittent connections.
Setup procedure that prevents common problems
- Identify the signal source. Confirm whether the chosen speaker wires are full-range, filtered, amplified, or differential.
- Disconnect the battery according to the vehicle service procedure. Some vehicles require radio codes or special precautions after power loss.
- Make signal and ground connections. Use secure crimp or solder-and-seal connections and route RCA cables away from the main power cable where practical.
- Set the LOC output low. Start with the converter and amplifier gains near minimum.
- Set the factory radio to a clean reference level. A useful starting point is about 75–80% of maximum volume, below audible clipping.
- Raise the LOC output gradually. Stop if distortion, hiss, or harshness appears, then set the amplifier gain to reach the desired level.
- Adjust bass restoration last. If the factory system reduces bass at higher volume, increase AccuBASS or an equivalent control only until the response is balanced.
- Test shutdown. Lock the vehicle, wait through its normal sleep period, and confirm that the amplifier and LOC turn off.
For example, if a converter output is set too high and the amplifier gain is then increased by another 6 dB, the system receives roughly twice the voltage from that gain change. That can consume headroom quickly. Make one adjustment at a time and listen for clipping rather than chasing a particular knob position.
Bottom line
Buy a two-channel LOC for a simple subwoofer addition, and choose the LC2i Pro when factory bass roll-off is a concern. Choose the LC7i for a full multi-amplifier system with separate front, rear, and subwoofer feeds. Choose the Wāvtech linkDQ when your factory system requires more sophisticated routing and correction. A compact PAC or KICKER converter is sufficient for a straightforward, space-constrained upgrade, provided the factory signal is full-range and stable.
