How to Wire High Level Input on Amp

Audio amplifiers for cars come in many different configurations. One of the functions of an amplifier is to accept a signal from one source like your radio and improve the sound quality and speaker level input to give you a better listening experience.

Now, there are a few ways to make this happen and one of them is to connect more than one amplifier to get the desired outputs. Here’s how you can do that by using low and high-level inputs either exclusively or in combination.

If you are not sure about how to wire high-level input on an amp, here’s a look.

What Is a High-Level Input on a Car Amp?

If you didn’t know it already, a high-level input is just another way of saying you will use the speaker wire lead behind the radio instead of RCA cables and connect them to the amplifier. This is how you get an input signal to the amp.

Now, a lot of factor radios don’t come with RCA jacks which makes it very difficult to install an amp in an audio system. So, manufacturers came up with a solution that requires you to use high-level input so that their products can be connected and played in the newer cars.

Now, we will tell you how to hook up an amp without RCA jacks but if you have a pair of them, it’s not a problem. Let’s take a look at the connections and how you need to wire them for the output you desire.

Which Type of Connection Do I Need?

Typically, factory audio systems that have high-level inputs do not sound nearly as good as low-level input connections. This is true even when you use aftermarket stereo systems.

But not many people pay attention to this because the output does not seem as different. They can even degrade the signal if the connections are not made properly.

This is also because high-level input systems need you to make changes to the wiring of the car. Instead, a lot of people just use RCA cables. This is not a bad way to go because, in the end, it does give you flexibility in terms of installation irrespective of the type of system you are dealing with. Here are the popular choices to wire high-level input on an amplifier.

1.     Use a Line Output Converter

A line output converter or an LOC has a high-voltage resistor and a transformer. It connects to the amplifier using an RCA patch cable. You need to ground the transformer of the device with LOC cables meant for this purpose.

The line output converter also has an RCA adapter for amp which connects to the stock radio and takes the speaker-level input signal coming in at high voltage and converts it into a preamp-level signal that brings it to an acceptable power range for the amplifier at hand.

A line output converter also has a feature that lets you adjust the gain so that the output is tweaked. This makes sure that the subwoofer is not overworked when it is balancing the output trim level of the amplifier.

If you want the amplifier to accept the high-level input directly, you can use a high-to-low converter and that is what an LOC is for. This is a popular choice because the connection uses RCA cables which provide an input signal directly to the amp.

Using a line output converter makes it easy to control the different signals coming in from various channels to the radio. Here’s how you can wire it.

  • Step 1: Disconnect the negative terminal of the battery to make sure there are no electrical problems like short circuits or blown fuses.
  • Step 2: You need to locate the wire that connects to the LOC. For this, you will need to take out the factory head unit. It is best to check out the user manual to be able to do this safely because you might have to remove a few screws to take off the panels.
  • Step 3: Take a look at the high input amp wiring diagram along with the diagram for the stereo output wires. Learn about the connections and the wiring on your LOC. This will make it easy for you to connect the wires to the corresponding terminals.
  • Step 4: Remove about an inch of the insulation of the LOC wire and the stereo wire. Now connect the LOC’s front left to the stereo wire’s side. And do the same with the front right wires too.
  • Step 5: Cover the connection with electrical tape and make sure the wires are secure together. Plug in the RCA cables from the LOC to the amplifier.
  • Step 6: Connect the battery, switch on the stereo and test the amplifier and speakers.

2.   Use RCA Cables

When you are dealing with a 4-channel amp and have chosen RCA cables to wire it, you will need to buy a second pair and an amp wiring kit, if you don’t have them already. Note that the kit is likely to have a cable for a 2-channel amp which you might need.

Before you start the process, make sure you have:

  • 100-feet speaker wire that is 18 gauge or more
  • Butt connector and crimp tool
  • Electrical tape
  • Cutting pliers
  • 6-inch wire ties
  • Testing meter

Typically, for these kinds of installations, you need to have 18’ cables. The idea is for the cable to be long enough to suit most cars. If the cable is longer than you need it to be, you can always hide it under the back seat or make a similar adjustment. But not much you can do if it is shorter. Now, for the process. Here’s how it goes.

  • Step 1: Connect the four RCA cables to the outputs in the front and the rear. If you are using a line-level converter, the same logic applies.
  • Step 2: The RCA cables sometimes have markings that tell you which is left and which is right. In some cables, the color of the cable is used to tell the difference, in which case, the cables in the lighter color or white are the left channel.
  • Step 3: Once you connect the RCA cables, you must mark them for future reference. Place a tape on one of them or use a marker.

And you are good to go. Switch on your radio and speakers and test out the amplifier.

Use Speaker Wire

Another way of wiring high-level input on an amplifier is to use the speaker wires. Using this method, you will be using the power coming from the harness of the factory radio to get an output from the speakers.

These wires are behind the radio which means you will have to remove them carefully to access them. Here’s how you connect them.

  • Step 1: Identify the wires that are meant for the speaker of your choice. Sometimes, you can tell the difference because the positive wires are in solid color and the negative ones have a stripe of another color on them.
  • Step 2: Cut the insulation of each wire to about an inch. Connect the wire from the radio to a wire that needs to go to the amplifier’s input end.
  • Step 3: Connect the wire that is connected to your speakers to the wire that is connected to the amplifier’s output.

Switch on the radio and speakers and test your amplifier.


Q: Is It Better to Use High-Level Inputs on Amp?

A: A lot of amplifiers these days work well with high-level inputs in the 10-volt range. So, you can connect the speaker with the existing radio’s connections and plug it into the amp. This makes installation easy and gives you better output too.

Q: What Is the Difference between High and Low Input on Amp?

A: High-level inputs come in handy if you want to connect a factory radio to an amplifier that doesn’t come with RCA connectors. This takes the signal from the speaker and sends it to the amp as the input.

Low-level inputs, on the other hand, use RCA cables to connect the audio source with an amp. Factory radios usually don’t have these inputs.

Q: Do RCA Cables Go to Input or Output on Amp?

A: RCA cables usually go into the input socket of the amplifier. For this, you need to connect the red cable to the amp’s red input socket and you’re done. Play a track and see if the connections are in place.

Wrapping Up

A lot of people like to leave the factory radio in place. But if you are looking for an upgrade that involves integrating an amplifier into the audio system so that your speakers have more power, you need preamp outputs that make the connections possible.

Many factory radios don’t come with these connections, so you need other ways to make it happen. Of the three options we have discussed in this piece, using an LOC is the most affordable.

Last Updated on November 20, 2021 by Danny Reid