Best Line Output Converter of 2024, Tested and Reviewed

Adding an aftermarket amplifier is one of the easiest ways to improve your car’s audio quality.

And you should have it in your vehicle before you go for an aftermarket subwoofer/speakers. It’s mainly because factory amps don’t have the strength the power them properly.

Connecting these amps with a 3rd-party head unit is straightforward.

But what if you want to connect them to a factory head unit instead?

The head units are getting more difficult to replace these days, after all. And it makes sense to leave them untouched if your vehicle is new.

However, the main problem with factory head units is that they lack preamp outputs. They feature speaker-level output that is not compatible with most amplifiers.

So you have different options here.

You can either get a new head unit, get a new amplifier with speaker-level inputs, or use the existing amp + convert those speaker-level signals into RCA-level signals.

The last option is definitely more cost-effective.

This is where the Line Output Converters (LOCs) come into the equation.

These LOCs are installed between the head unit and the amplifier. And they convert the speaker-level signal into the RCA-level preamp signal.

You need to connect the radio’s speaker wires to the LOC’s inputs and then connect the LOC to the amplifier using RCA cables.
In this post, we’ll discuss some of the best line output converters you can have in 2023.

1. Scosche LOC2SL: Best Budget 2-Channel LOC

Our first line converter is the Scosche LOC2SL.

It’s a low-profile, passive LOC that does its job without breaking your wallet.

There are a couple of things that make it unique among entry-level adapters.

The first one is the built-in remote trigger. This wire is crucial because it can send the turn-on signal to an aftermarket amplifier. This feature can be handy if you’re not using the remote turn-on wire of your head unit.

The second one is the bass knob that allows you to control the bass level of the subwoofer remotely. This knob is handy as you can place it wherever you want and control your subwoofer.

And its smaller size allows you to fit it in almost any spot in your vehicle.

As far as the specs go, this LOC is compatible with up to 90W per channel. But it tends to distort sound if the voltage level is too high. That’s why you should only use it in entry-level audio systems that don’t feature any external factory amp.

As far as the installation process is concerned, this is how it goes.

First, you’ll need to connect speaker wires to your amplifier. Then, you’ll use a spare remote turn-on cable and connect it to the remote input of the amp and the remote wire of this LOC. After this, the adapter’s ground wire is paired up with the that of the the amp. Then this combined wire is connected to the ground input of the amp.

Similarly, pair the power wire from the adapter and the power wire from the battery together and connect ’em to the amp.

Now, plug RCA jacks into the RCA output of the adapter. The white jack will be plugged into the white output and the red jack will be plugged into the red output.

Similarly, connect the other ends of the RCA cable to the amp. If you’re using a mono-amplifier, you should combine these two jacks into a single one using a y-adapter and then plug it into the amp.

Lastly, we’ll need to take care of the speaker wires of the adapter. The grey wires correspond to the right speaker, while the white wires correspond to the left one. We’ll strip the wires going into each of the speakers and expose their strands.

Then, we’ll take a new speaker wire and twist its strands onto the exposed area of the speaker wires. Then, we’ll connect the other ends of the new speaker wire to the speaker wires of the adapter.

You can also solder these connections for extra durability.

Although this process is straightforward, you can watch the video above in case of any confusion.

2. KICKER 47KEYLOC: Best 2-Channel LOC

In case you’re looking for a 2-channel LOC but want more bells and whistles, there’s Kicker 47KEYLOC for you.

Coming in with two 10V preamp outputs and two 400W speaker-level inputs, it’s slightly cheaper than the high-end LOCs but gives you a big performance leap against other entry-level adapters.

In terms of size, it’s quite bigger than other 2-channel LOCs and features an all-black color scheme. Besides the usual inputs and output gain controls, you’ll see a set of 5 LEDs on its top side.

The LEDs are part of the built-in RTA functionality of this adapter. With this feature, the 47KEYLOC can detect the frequency of speaker wires you’re tapping into. This way you can easily identify whether a particular speaker is a tweeter, midrange speaker, or woofer.

The first LED represents low frequency (20Hz-200Hz), the second represents the mid-frequency (200-2000Hz), and the third LED represents the high frequency (2000Hz-20000Hz).

Once you’ve tapped into speaker wires and connected them to this adapter, different LEDs will illuminate depending on the speaker type. For example, if you’ve tapped into a midrange speaker and subwoofer, the mid and low-frequency LEDs will illuminate but the high-frequency LED will not.

To use this feature, you’ll have to turn the input gain down and the volume level up halfway. After this, you need to download the pink noise track using the link in the owner manual. Then, you’ll have to turn the amp gain up until these LEDs illuminate.

Speaking of the owner manual, 47KEYLOC doesn’t come with any physical manual. Instead, you’ll have to scan the QR code on the product box from your phone, and it’ll take you to the latest version of the owner manual.

Once you’ve connected all wires to their speakers, you can utilize 47KEYLOC’s built-in DSP to do several corrections (Factory EQ correction, time correction, frequency response correction, etc.) to the audio signals. For more info, check out the Kicker Test Tones.

Since it’s an active LOC, you need to send a remote signal to turn it on and off. For this purpose, there’s the DC offset that uses speaker wires to turn on and off. Furthermore, it has a remote turn-on output which you can use for the aftermarket amplifier to turn that amplifier on/off.

With that said, some people have reported that this feature is not perfect and the adapter can stay powered on for up to 10 minutes after the vehicle is shut off.

The other downsides I can think of here are the length installation process and the relatively high price. The second one is a big deal as you’d expect a LOC with this price to have 4 channels instead.

3. AudioControl LC7i: Best 6-Channel LOC

The LOCs we’ve discussed so far feature two channels. It means they’re more suitable for full-range factory audio systems.

But what if you have lots of components speakers installed in your vehicle. For such complex systems (featuring different tweeters, midrange speakers, and woofers) you’ll need something like AudioControl LC7i.

This is a 6-channel LOC which means it can take two +ve and -ve input in those channels from each of those three speakers types. Even if you’re using conventional front and rear speakers in your vehicle, you can plug their wires in 1-4 channels and have the last two reserved for a subwoofer.

Each of these channels comes with a dedicated output level knob. And there’s a dedicated LED to indicate when you reach the maximum level.

Being an active LOC, its output can be as high as 8.5V. This higher output allows you to set a lower gain for the aftermarket amplifier which, in turn, means less noise in the audio.

It comes with the GTO technology that turns the LOC on by sensing the speaker inputs. After this, you’ll have a run a remote wire from the LOC to your aftermarket amplifier to add this functionality to it.

Then, there’s AccuBass. It’s a well-known fact that factory speakers lack the performance you usually get with their aftermarket counterparts.

So, to protect these speakers from damage, the factory head units roll-off the bass whenever you increase the volume level. While this technique helps them to last longer, it removes the bass punch from your car music.

Using AccuBass, you can add that missing bass into your audio signals before sending them to your subwoofer.

Another noticeable feature is the channel summing.

In factory component speakers, the audio signal is already divided through a crossover and sent to respective speakers. It means when you’ll tap the speaker wires and bring that signal into the LOC channels it’ll be already divided into 2/3 parts. Using channel summing, you can combine these channels to get a strong full-range audio signal.

Lastly, there’s an optional AudioControl ACR-1 wired remote. This is an optional knob that allows you to adjust the bass output – similar to the one in Scosche LOC2SL.

As far as the downsides are concerned, there’s nothing actually. If I have to nitpick, then it would be the relatively higher price for a LOC. That’s why you should only go for it if you already have other high-end components in place.

Things to look for in a Line Output Converter

Now we’ll discuss some general factors to look for when buying a hi-lo adapter.

Specs

Some of the common specs to look for in a LOC are the voltage it can accept from speaker-level inputs, preamp-level output, and frequency response. The last one is important because some cheap LOCs don’t properly pass the signal if it’s too high or too low.

Active vs Passive LOC

The Line output converters are mainly divided into two types: Active and Passive.

Passive LOCs are generally cheaper but offer only the basic functions you can expect in a hi-lo converter. These types of LOCs are used if you’re using a factory audio system with no external amplifier.

On the other hand, we have active LOCs. These are advance LOCs that give you cleaner sound signals and come with many additional features such as bass restoration, channel summing, remote turn-on, de-equalization, etc.

Unlike passive LOCs, they do require 12V constant and ground wires to work.

These LOCs are usually used when you’re your factory audio system has a factory amplifier. And you’re taking the speaker-level signal from your factory amp to the aftermarket amp since these signals would be too powerful for passive LOCs to handle.

Internal vs External LOC

Some aftermarket amps come with a built-in LOC. While these amps can be considered, they give you much less room as far as customization goes.

Moreover, if you want to upgrade your amp in the future, you’ll have to get a new LOC anyway. Therefore, you should always go for a standalone LOC unless you don’t want any car audio upgrade for the next 2-3 years.

Additional Features

Some additional features you can expect in a high-end LOC are:

Bass Boost:

Factory head units tend to decrease the bass response as soon as you turn up the volume more than half. The reason behind this is the protection of factory speakers that can’t handle the deep bass properly.

But since don’t have any of such limitations in 3rd-party speakers, we don’t need a reduced bass. This is where the Bass Boost comes in handy as it adds the required amount of bass to the speaker-level signal.

Remote turn-on Capability:

Aftermarket amplifiers need a trigger to turn on and off. This is usually done through the remote turn-on wire.

But if you can’t use this wire for any reason, you should get a LOC with a built-in remote wire. All you need is to connect this wire to the remote input of your amplifier.

Channel Summing:

The summing function allows you to combine multiple input signals to the main channel output. It is typically most used when connecting to a factory system that has dedicated speakers for just the highs and mids. You can use the summing function to sum those signals to create a full range output.