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How to Hook Up 2 Amps with 1 Power Wire

Every now and then We get e-mails and comments from inexperienced car audio enthusiasts who like to rock out — really loud and hard. One recent one asked, “How can I hook up 2 amps with 1 power wire?”.

This might seem puzzling at first, but it’s actually not that hard at all. I mean, this really isn’t all that different from installing one single amplifier.

Actually, you can wire two amplifiers, or even multiple amps, in one car audio system, but it takes some extra work, time, and most importantly planning.

Essentially, the most crucial things you need to take into account when you wire in multiple amps are how you will deal with the power cable, how to properly ground each amp, and how to make the turn-on signal from your head turn on multiple amps simultaneously.

Can You Have Multiple Amps in One Car Audio System?

Absolutely. You can install any number or combination of amplifiers in a car audio setup as long as you wire them in properly. However, your electrical system must be up to the task.

If you add in too many amps, and they draw too much power, you may need to consider upgrading your stock electrical system. One of the most common symptoms of amplifier overloading the alternator is flickering or dimming headlight. This happens because your amp(s) is starving them, which leaves you with two basic solutions: downgrade your sound system, or upgrade your charging system.

As to whether it’s better to use multiple amps or one multi-channel amp to drive your speakers, that depends on a wide variety of factors including what you’re trying to achieve, your own personal preference, the amount of available space in your car, and most importantly your budget.

The most common reason to wire in multiple amps is to have one multi-channel amp powering your main speakers and a second mono channel amplifier powering a subwoofer.

If you decide to opt for multiple amps, the process of multi-amp wiring is relatively similar to single amp setups. You have a couple of options, but it’s of paramount importance to take the increased current draw into account.

How to Hook up 2 Amps With 1 Power Wire

As we’ve mentioned above, there are three essential elements you’ll be dealing with whether you’re wiring one or multiple amplifiers and those are:

  1. Power wire
  2. Ground wire
  3. Remote turn on wire

Down below, we’ll explain in detail how each of these wires should be attached when you’re installing a second amplifier in your car.

1. How to run the power wire

When it comes to amp power wire, you have two options: either run separate power cables for each amplifier, or run a single cable that feeds all of them. Depending on your setup, either one of these options may work out for the best.

Running a single power wire is the best way to go about it and is the most elegant solution. If you decide to opt for this option, ensure the power cable is thick enough to accommodate your amplifiers’ increased demand for electrical current or the amplifiers won’t operate properly or put out their rated power.

In other words, due to the fact that your power cable needs to accommodate the current draw from all of your amps simultaneously, it must be significantly larger in gauge than the recommended gauge for your individual amp. For example, if 8 gauge wire is the recommended size for your amplifiers, it’s highly recommended to use 4 gauge cable for your run to the battery in order to ensure proper current flow. The more demanding the audio system, the larger gauge wire you will need to use.

The best – and neatest – way to wire multiple amplifiers to a single power cable is to use a power distribution block. The latter is an economical and convenient way of distributing an electrical circuit from a single input source, to several devices in the branch circuit.

Using a distribution block will not only save you from the hassle of running multiple power cables through the firewall, but it’ll also allow for a clean installation.

A distribution block can also be fused, which is helpful in situations where amplifiers don’t come with built-in fuses.

2. How to run the ground wire

Rather than grounding each amplifier individually, use a ground distribution block to wire your amplifier’s grounds to a single connection point to prevent noise/interference in your set up, and to avoid ground loop issues.

In a mirror image of the power distribution block, each of your amplifier should be connected to the ground distribution block, which in turn should be connected to a good chassis or subframe ground that’s sanded down to bare metal; preferably within eighteen inches of the amplifiers’ location.

It must be noted that your amps’ ground wires must be the same exact size as the power wires. Moreover, the cable you run between the ground distribution block and the grounding spot must be of the same size as the cable running between the battery and power distribution block. This is to ensure smooth and proper current flow.

3. How to Run the Remote Turn-on Wire

A remote turn on wire is a Blue wire (typically with a white stripe) located on the back of the headunit. Its main function is to “tell” your amplifier to turn on whenever the head unit is powered on. Without the remote turn-on signal, your amplifier won’t turn on.

There’s a number of different ways to turn on a car amplifier without remote wire. However, using the turn on wire from the head unit is the best way to go about it. However, the problem is that sometimes a remote turn-on signal isn’t strong enough to to turn on multiple amps at once. A great workaround this issue is to connect the turn-on leads from your amps to a relay, which is triggered by your head unit. Using a 12v relay is really a slick way to turn on multiple separate amps at once.

P.S: Running multiple amplifiers off of one remote turn on lead should be avoided at all costs. This is because you can easily Kill that remote lead on your head unit when you’re pulling too much power through it.

 

A relay is an electromagnetic switch that uses a small electric current to trigger a much bigger one. In other words, it converts small electrical stimuli into larger electric currents.

In this case here, rather than receiving power from the head unit, the relay should be connected to another source of battery voltage — either from the fuse box or directly from the battery. This will effectively isolate the turn-on signal from the head unit from your amplifiers, which will allow your amps to turn on and hopefully avoid any issues with current overload.

4. What to Do About the Speaker wires

The last part of connecting multiple amplifiers to one source is attaching the head unit to your amp. This depends on the outputs on your head unit. If you have a head unit with multiple preamp outputs, then you can connect each set of outputs directly to one of your amps.

If your head unit doesn’t have multiple preamp outputs, then you’ll have to check your amplifiers. Some amplifiers are featured with RCA pass-through circuit, which allows you to connect multiple amplifier together. What this circuit does is that it allows the signal from a source component to travel through an intermediary component without alteration. In this case here, you can connect the pass-through outputs on your first amp to the preamp inputs on your second amplifier.

If neither the head unit has multiple preamp output, nor the amplifiers have the pass-through functionality, you’ll need to use Y adapters to split the signal between your amplifiers.

If your head unit doesn’t have any preamp output at all, you’ll either need amplifiers with speaker-level inputs or a line output converter to convert speaker-level output signal (high-level amplified signal) into RCA preamp-level signal (low level signal).

If you’ve followed all steps listed above, you should end up with something like in the diagram below:

Alex Brown

Hey There, my name is Alex Brown, I'm an LA-based sound engineer with over 10 years experience installing, troubleshooting, and repairing commercial, automotive, and household sound equipment. I've installed highly competitive car audio systems, and everything from navigation systems to full car stereo systems, remote starters, alarms and beyond. I enjoy creating solutions and simplifying everyday needs. I also love helping people get great sounding gear, thereby, saving the world from bad sound one customer at a time.

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