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What is a speaker to line level converter?

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line and speaker level

An amp can be used with a factory head unit if it has speaker level inputs or you use a line level converter.

Image courtesy of Jordanhill School D&T Dept, via Flickr (Creative Commons 2.0)
Question: What is a speaker to line level converter?

I want to upgrade my car audio system, but I have one of those factory head units that’s all tied into everything from the heater and a/c to nav system, so I’d like to leave it in place if possible. I’ve heard that can be a problem when it comes to installing an amplifier, which I’d really like to be able to do. Someone told me that the only way to connect an amp to a factory stereo is to use something called a “speaker to line level converter.” What exactly is a speaker to line level converter, and will something like that work with the sort of upgrades I want to make?

Answer:

First of all, you’re not alone in your desire to beef up your car audio setup without touching your factory head unit. This has become more of an issue in recent years, due to highly integrated infotainment systems, but there have always been people who just prefer the look or feel of a factory head unit.

You’re also on the right track as far as potential upgrades are concerned. Premium speakers can help out a lot, even without upgrading anything else, but adding an amp will give you a lot more power to drive those speakers.

Before you go out and buy anything, you’ll want to make sure that your factory system doesn’t already have an amplifier. Most don’t, but if yours does, it will simplify matters a lot, since you may be able to just swap out the under-powered factory amp for one that better suits your needs.

Even if your factory system doesn’t have an amp, there’s also a chance that your factory head unit came with preamp outputs. This isn’t an extremely common thing, but it is worth checking out to potentially save yourself some time and effort. If it does have preamp outputs, then you’re good to go.

Speaker Level Vs. Line Level

In most cases, factory car stereos don’t have external amps, and factory head units don’t include preamp outputs. The most common situation for a factory car stereo system involves a head unit with a built-in power amp and speaker level outputs. This is also the most common design for aftermarket head units, but a lot of those also include preamp outputs.

In order to understand the difference between speaker level and line level signals, it’s important to remember the fact that your head unit has a built-in power amp. If it didn’t, it wouldn’t be able to drive your speakers at all, because the un-amplified audio signal is simply too weak. That un-amplified, analog audio signal is known as a “line level” signal. After it is passed through an amplifier, whether it’s an internal or external amp, it becomes a more powerful signal known as a “speaker level” signal.

Most amplifiers only have line level inputs, so they can only be used with head units that provide line-level outputs. However, some amps have speaker level inputs. If you want to add an amp to a car audio system without replacing the head unit, and you haven’t already bought the amp, then that’s the easiest solution. Installing this type of amp is a simple matter of connecting your head units speaker outputs to the speaker level inputs on the amp, and then connecting the amp itself to your speakers.

Using a Speaker to Line Level Converter

The other option is to use a speaker to line level converter. In simple terms, these devices lower the power of the speaker outputs to a point where it is similar to the power level of an actual line level output. That allows you to essentially connect the speaker level signal without overloading your amp (which is designed to amplify a weak line level signal.) This isn’t the same thing as having actual preamp outputs, but it does allow you to use a factory head unit with virtually any power amplifier.

If you want a lot of flexibility with the amp you buy, or you want to retain the option to upgrade your head unit (without buying a new amp), then a speaker to line level converter is a better idea than an amp that has speaker level inputs.

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