A Close Look at Car Audio Line Output Converters

Line Output Converters

Car audio installations often involve managing voltages. Your vehicle’s electrical system must generate sufficient voltage to power your radio and amplifier. Amplifiers, on the other hand, require increased voltage to drive speakers. When adding an amplifier to a factory-installed audio system, a line output converter is typically needed to adjust the voltage and make it compatible with the new amplifier. In this article, we will delve into how these converters work and explore the various options available to simplify the process of upgrading your car audio system.

What Is a Line Output Converter?

These integration devices, known by several names such as high-to-low converters, speaker input adapters, or line level converters, have a straightforward purpose. They take an audio signal intended for a speaker and lower its voltage to connect it to the RCA preamp input on an amplifier or signal processor.

Amplifiers typically accept a maximum input voltage of 4 to 6 volts. Exceeding this voltage can lead to clipping and distortion. However, even a basic car radio can produce around 6.5 volts of output on the speaker wires, while a small amplifier can deliver 13.4 volts. In the case of a subwoofer amplifier integrated into a factory-installed audio system, the voltage can easily exceed 30 volts.

How Do Line Level Converters Work?

There are two common types of converters available. The first and more affordable option incorporates small audio transformers to reduce the voltage. These transformers have more turns on the input winding than the output, resulting in a 50-60% voltage reduction. These passive devices don’t require a power and ground connection to function.

The second type, and the most popular, includes circuitry that provides a low-impedance output to the new amplifier. These converters require a power, accessory, and ground connection. They can also act as line drivers to increase the output voltage compared to the input. If your source unit only provides a low voltage output, adding a line driver can boost it to improve the signal-to-noise ratio.

What To Consider When Shopping for a Line Output Converter

When looking for a quality line output converter, there are a few key factors to consider. Ensure that the converter can accept the voltage levels present on the speaker-level inputs and adjust them accordingly. Additionally, understanding the output impedance on the preamp side is crucial, with lower impedance being preferable.

The frequency response of the device is also important. Transformer-based converters might not pass deep bass or high-frequency audio information as effectively as active units. Look for a converter with a frequency response spec of at least 10 Hz to 40 kHz, with a tolerance of 1 dB.

Noise and distortion specifications should not be overlooked. Aim for a total harmonic distortion (THD) specification of no more than 0.05% and noise levels quieter than 110 dB.

Remote Turn-On Detection Features

Many line output converters offer an amplifier turn-on output signal. This feature is particularly useful when adding a subwoofer amplifier to a factory-installed sound system, as there may not be an easily accessible wire that goes to 12V when the radio turns on. These converters can monitor the speaker wires or input connections for voltage changes and activate the output accordingly. However, there can be instances where the unit is triggered falsely, such as when a car door is closed and momentarily pressurizes the interior, causing the speakers to produce a voltage spike.

Bonus Line Output Converter Features

Several line output converters come with additional features that enhance their functionality. For example, remote level control allows you to adjust the subwoofer volume relative to the rest of the system. Another popular feature is an equalizer, which can boost frequencies that may be attenuated in the factory source, resulting in improved bass extension and impact.

Some high-quality converters also include speaker load simulators. If you’re adding an amplifier to drive factory speakers, these simulators ensure the amplifier sees a proper load impedance.

Channels and Signal Summing

Line output converters are commonly used when adding a subwoofer amplifier to a factory-installed source unit. However, they are also suitable for adding amps to drive front and rear speakers. Some vehicles with branded audio systems can be easily upgraded using multi-channel line output converter interfaces. These converters can sum signals together from multiple inputs, but it’s essential to ensure that the audio signals are in phase. If the signals are out of phase, the frequency response of the audio signal can be compromised.


When planning to add an amplifier to your factory-installed audio system, a line output converter is often necessary. Ensuring a smooth connection between the amplifier and the audio system, line output converters play a vital role in improving the sound quality of your car’s audio. Consider the various features, voltage compatibility, and impedance of the converter to make an informed choice. Visit a specialty mobile enhancement retailer to explore compatible solutions and achieve exceptional sound in your vehicle.

Line Output Converters

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