When it comes to wiring up an aftermarket amplifier for a car stereo system installation, there are a number of roads that can be taken in regard to approach. It’s all dependent on the gear being installed, the types of connectors available on the equipment, and the overall goals of the system itself.
Most middle to high level styles of mobile audio system installs utilize an amp’s RCA ports for what is arguably the cleanest-sounding connection from the system’s head unit (radio/receiver) to the amp itself, but there are scenarios which demand a different solution be found, specifically with head unit has no RCA outputs on the back. With that being said, we’re going to take a look at how to hook up an amp without RCA jacks.
Ultimately, there are three ways to deal with this install dilemma:
- Speaker wire to RCA adapter
- High-level inputs on an amp
- Line output converters.
Each come with their own set of advantages and challenges, like everything else, but worry not – the following information is going to clear up any misconceptions about either approach.
#1 Speaker Wire to RCA Adapter
To begin with, it can’t be stressed enough just how important an outboard power amplifier is in a mobile audio system. For those who have never experienced car stereo beyond the limits of their vehicle’s factory setup, the difference is staggering – from the jaw-dropping dynamic range offered by an amp’s high-current power to the raw muscle that drives thumping subwoofers in the trunk, amplifiers provide the visceral horsepower required to make music truly come to life.
This is to say nothing about the way a good amp will overcome that annoying road noise in many makes of cars and trucks, which can be especially irritating if the windows of the vehicle are down and the car or truck is at highway speeds.
But what many novices in the car audio world fail to realize is that a vehicle’s factory radio can in fact be used with an outboard amp – it just takes some creativity and knowledge of the necessary accessories to hook it all up. An amp can help you get the most from your factory system, especially when it comes to larger vehicles like vans or full-size SUVs, where it can be especially challenging to achieve a clean, powerful sound.
This is where we get into our first solution – adapter cable from speaker wires to RCA plug.
If your amp can accept a high level input on the RCA’s (see specifications your amplifier) you can hook this adapter up to your car’s rear speaker wire harness and then plug into your amp’s RCA cable input.
Best adapters you can buy:
#2 High-Level (or Speaker-Level) Inputs on Amplifiers
The second option is a high-level inputs, sometimes referred to as speaker-level inputs.
What is a High-Level Input on a Car Amp?
Because factory radios don’t have dedicated outputs for amplifiers (“RCA” or “preamp outputs”), most outboard power amps come with high-level inputs, which enable you to tap into the factory speaker wires for signal flow. They’re referred to as high-level inputs because the voltage level is significantly higher than that of a standard preamp output connection.
Regardless, these inputs convert the high-voltage to a version the amplifier can handle. Once connected, the result is clean, well-defined sound, with high-level inputs coming standard on a variety of two and four channel amps, as well as mono (one channel) subwoofer amplifiers.
How to Wire a High-Level Input on an Amp
The installation of an amplifier using high-level inputs isn’t much different from the procedure used when wiring one with preamp outputs. Before anything is even attempted, it is always advised that you disconnect the negative terminal from your battery to protect against a possible short circuit.
Working from your vehicle’s passenger cabin, you will run the red power wire from your amp kit through your vehicle’s firewall, route it to the battery and connect it to the fuse holder. Mount the fuse holder and secure the connections to the head unit and battery; this procedure will yield your power. At this point you’ll also route your red (power) and blue (turn-on) wires under door panels (or seats) to your amplifier.
Now that your power is tapped, it’s time to get into receiving an actual audio signal. For each speaker (or subwoofer) that you plan to drive with an amp, strip back a small part of your vehicle’s color-coded left and right speaker wires, then splice in the wires that lead to your amp (crimp or solder, and secure the connection for optimum performance).
If your amp is being installed in your car’s trunk, it’s a relatively short path to the rear deck speakers or a subwoofer, so reaching the amp shouldn’t be a problem. Driving front seat speakers will require you to run wiring under a door jamb or the floor carpeting to reach the speakers. Similarly, if your amp is mounted under the front seat, the front speakers will be easier to reach than the rear ones.
#3 Line Output Converters (LOC)
The third option for putting together a system without RCA jacks comes in the form of a line output converter, a device used by many installers who have customers that don’t want to get rid of any aspect of their factory stereo – they simply want to add amplifiers and subwoofers.
What is a Line Out Converter?
This RCA adapter for stock radio that converts the high-voltage, speaker-level signal to a preamp-level signal that’s acceptable to a power amp. An “LOC,” as they have come to be known, consists of a transformer and a high-voltage resistor, and connects to your amp using a standard RCA patch cable. The transformer of this device should be grounded, with most line output converters coming with a wire for that exact purpose.
LOCs also usually come with an adjustable gain feature, so the output feeding an amp can be tweaked to a certain extent (this is good for ensuring subwoofers aren’t overdriven when balancing an amp’s output trim levels).
What Does an LOC Do?
As we touched on in the above section, an LOC converts the high-voltage, speaker-level signal to a preamp signal that a power amp can use. This is especially helpful when installing a two channel or mono amplifier to an existing factory radio (or even some aftermarket systems).
Most LOCs feature up to four volts output and signal-sensing turn on with the ability to drive a relay; some also include convenient remote-mountable volume controls for precise adjustment over subwoofer amplifier level from the driver’s seat.
Some best LOC you can buy:
How to Hook Up a Line Out Converter
The first thing you’ll need to do is hunt down the leads connecting your vehicle’s factory installed radio and amplifier to the speakers. From our experience, these wires are located just behind the head unit. From there, you will use wire strippers to strip away one-inch of the wires’ insulation – from each wire – so that the right channel of the LOC can be attached to the right speaker and the left channel of the LOC can be attached to the left speaker.
Now, the next step is to solder the converter’s wires to the speaker wires and then seal that connection with either electrical tape or a heat shrink method. The LOC must then be secured to your vehicle at some attachment point before inserting RCA cables into it and running those to your amp.
The final steps involve balancing some levels so that everything sounds as clean as possible. This begins with adjusting your amplifier’s gains to a midway setting, and then turning on your radio so that you can adjust the volume to what you feel is a comfortable listening level. Slip the working end of a small screwdriver into the adjustment detents of the amp and adjust those gains until you sense distortion is creeping in, then turn the gains down until it disappears.
Finally, go back to your head unit and turn the volume up to ensure no distortion is being emitted by the amplifier. If you hear distortion, adjust the gains on the converter and amp in response.
Either way, a simple line out converter or an amp’s high-level input will get your system banging away pretty quickly, provided you’re willing to strip a few wires first.
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