How to add an amplifier or subwoofer to a factory head unit?
Your factory head unit doesn't have RCA outputs? Discover how to use a High/Low converter to add an amplifier, a subwoofer or improve your audio system without necessarily replacing the head unit.
Keep the factory head unit and add an amplifier
Many modern cars have a perfectly
integrated head unit but without RCA outputs.
This does not mean that it is impossible to add
an amplifier or a subwoofer.
A High/Low converter, also called
a high-level to RCA converter or
LOC, allows in many cases to recover
the original audio signal.
head unit
outputs
Speakers
What is a High/Low converter used for?
An aftermarket head unit often has RCA outputs allowing you to send an audio signal directly to an amplifier.
On many factory head units, these RCA outputs are not available.
The converter picks up the audio signal normally sent to the vehicle's speakers.
The signal is adapted so that it can be sent to the RCA input of a compatible amplifier.
You can keep the factory head unit, the steering wheel controls and the vehicle integration, while adding additional amplification.
Identify the right speaker wires
Before connecting the High/Low, you need to identify the speaker outputs that you want to use.
You need to determine in particular:
- The left channel.
- The right channel.
- The positive (+) of each channel.
- The negative (−) of each channel.
Bad polarity between channels can cause
phase problems and especially a strong decrease
in low frequencies when the signals are summed.
Do not rely solely on the color of the cables:
use the vehicle's wiring diagram and appropriate
testing methods.
Where to pick up the audio signal?
Depending on the vehicle, the signal can be picked up in different places.
When the speaker outputs are directly accessible on the head unit harness.
It is sometimes easier to pick up the signal directly on a speaker's wiring.
The signal can also be picked up on an accessible part of the audio harness.
On some systems equipped with factory amplification, the signal can be picked up at the output of this amplifier if the equipment used is compatible.
Make sure you pick up a signal containing low frequencies
On a simple installation, the signal sent to the speakers can be wide enough to power a High/Low converter.
But on some modern vehicles, the outputs can be filtered individually.
A door speaker can, for example, receive a signal whose lowest frequencies are already attenuated.
If you pick up this signal for your subwoofer, your new amplifier will not be able to recreate the frequencies that are no longer present in the original signal.
Connect the High Level inputs
Once the right channels are identified, connect them to the high-level inputs of the converter.
The speaker outputs of many modern head units
do not work like a traditional audio ground.
Respect the wiring diagram of the converter
and that of the vehicle's audio system.
Does the High/Low converter need to be powered?
It depends entirely on the model used.
Passive High/Low
Some converters work without additional +12 V power. They use the high-level signal directly.
Active High/Low
Some models require a +12 V power supply and a ground to ensure conversion, signal detection or other functions.
Depending on the converter, the connection may require a permanent +12 V, an ignition-switched +12 V, a ground or other specific connections. Follow the diagram provided by the manufacturer.
What is the Remote output used for?
An amplifier generally has a REM or REMOTE terminal.
This connection is used to control its power-on.
head unit
12 V
Some active converters automatically detect the presence of the audio signal and then generate a Remote output to turn on the amplifier.
The exact operation depends on the model used.
Connect the RCA to the amplifier
Once the signal is converted, the RCA outputs of the High/Low can be connected to the RCA inputs of the amplifier.
RCA inputs
Use a properly shielded RCA cable and perform a clean installation to limit the risks of interference.
Set the converter level
Some converters have level settings allowing you to adapt their output voltage.
An output level that is too high can saturate the input
of the amplifier.
Conversely, a level that is too low can force
you to excessively increase the gain of the amplifier.
The level must be adapted to the input sensitivity of the amplifier and the characteristics of the converter.
A simple High/Low is not always enough
Modern audio systems can apply many treatments to the signal before sending it to the speakers.
- Factory equalization.
- Active filtering of the different speakers.
- Signal correction according to the volume.
- Low frequency reduction at high volume.
- Speaker delay.
- Load detection.
- External factory amplifier.
In these situations, a basic converter can work but give a disappointing audio result.
A specific interface or a DSP with high-level inputs can be a more suitable solution.
What is load simulation?
Some factory audio systems monitor the electrical presence of the speakers.
When a speaker is disconnected or the expected load is no longer detected, the system can change its operation or report an anomaly.
High/Low converters or specific interfaces
offer load management or simulation
adapted to certain factory systems.
This function is not, however, necessary
on all vehicles.
Add only a subwoofer
You simply want to boost the bass without changing the rest of the installation?
head unit
signal
amplifier
The High/Low does not replace the amplifier's
power supply wiring.
The amplifier must have a power supply,
ground, and fuse protection
correctly sized for the installation.
Does your amplifier already have a High Level input?
Before buying a converter, check the connections available on your amplifier.
Many modern amplifiers have high-level inputs built-in.
input
Speakers
If the amplifier directly accepts the level and type of signal delivered by the vehicle, the speaker signal can be connected directly to its High Level input.
High/Low or DSP?
To simply add a subwoofer to a standard setup, a good High/Low converter may be sufficient.
On a more complex factory setup, a DSP with high-level inputs can offer many more possibilities.
- Management of multiple factory channels.
- Precise level adjustment.
- Equalization.
- Active filters.
- Time delay management.
- Better integration of a complete audio system.
The most common mistakes
Incorrect polarity between channels can cause phase problems and a significant loss of bass.
On some vehicles, a speaker signal may already be heavily filtered.
Setting the High/Low level to maximum can cause signal saturation.
An active converter must be powered according to its manufacturer's instructions.
Do not automatically consider speaker negatives as a vehicle ground.
First check if your amplifier already has a compatible High Level input.
Checks before finishing the installation
- Check left and right polarities.
- Check that the chosen signal contains the necessary frequencies.
- Check the converter's power supply if it is active.
- Check the Remote's operation.
- Check the RCA cables.
- Set the output level correctly.
- Check for the absence of interference.
- Check that the amplifier turns on and off normally.
Key steps to remember
Check if your amplifier already has a High Level input.
Correctly identify the left and right speaker outputs of the factory installation.
Strictly respect the + and − polarities.
Check that the captured signal contains the frequencies necessary for your installation.
Connect the High Level inputs according to the converter's documentation.
Power the converter only if its operation requires it.
Connect the RCA and Remote to the amplifier when the converter has these outputs.
Correctly set the High/Low level and the amplifier's gain.
Frequently asked questions about High/Low converters
What is a High/Low converter?
It is a device that allows you to capture a high-level signal from a speaker output in order to obtain a signal compatible with the input of an amplifier, generally via RCA.
Can I install an amp without changing my factory radio?
Yes. Depending on the installation, you can use a High/Low converter or directly the amplifier's High Level inputs when they are compatible.
Can I add only a subwoofer?
Yes. It is possible to keep the factory audio system and add a mono amplifier with a subwoofer.
Do all High/Lows need a +12 V?
No. Some converters are passive while others are active and require power. Consult the documentation of the model used.
What is the High/Low Remote for?
On models that offer this function, the Remote output allows you to control the turning on and off of the amplifier.
Why do I have almost no bass after connecting?
Several causes are possible: incorrect polarity, filtered factory signal, inappropriate channel summation, bad converter setting or the vehicle's factory audio processing.
Can I capture the signal directly from a speaker?
Yes in many installations, provided that the signal is compatible and contains the necessary frequencies.
Can a DSP replace a High/Low?
Yes, if the DSP has compatible high-level inputs. For complex factory systems, this solution can offer more adjustment and integration possibilities.
You are not obliged to replace your factory radio
The absence of RCA outputs does not necessarily prevent you from adding an amplifier or a subwoofer.
A High/Low converter in many cases allows you to capture the factory speaker signal and send it to an amplifier.
Factory radio → speaker signal → High/Low → RCA → amplifier → subwoofer or speakers.
On recent vehicles or complex factory audio installations you must, however, take into account filtering, equalization, load detection and the vehicle's electronic architecture.
This guide presents the general principle
of installing a High/Low converter.
Connections can vary considerably
depending on the vehicle, the radio, the amplifier
and the converter used.
Always consult the technical documentation
of the equipment and the vehicle's electrical diagram
before making the connections.
Would you like to add a subwoofer or amp to your factory radio?
Don't know which High/Low converter,
amplifier or DSP to choose?
Sound Auto Concept can advise you
according to your vehicle and your installation.
Sound Auto Concept
1 Rue de la Manufacture Semely, 34120 Pézenas
09.85.13.66.35
fabrication@soundautoconcept.com