How to Wire Multiple Amps in Your Car

You can wire multiple amps in one car audio system

Wiring in one amplifier can be complicated enough, especially when dealing with a factory car stereo. The situation gets more complex when you add multiple amplifiers to the equation. You can wire two amplifiers or multiple amps in one car audio system, but it takes extra planning.

The main factors that you need to consider when you wire in two or more amps are how you will deal with the power cable, grounding each amp, and whether or not the remote turn-on signal from your head unit is strong enough to split between multiple amps.

Can You Have Multiple Amps in One Car Audio System?

The short answer is that you can use any number or combination of power amps in a car audio setup as long as you wire them in properly. The main proviso is that the charging system has to be able to provide enough juice in the first place. If you add in too many amps and they draw too much power, you may need to upgrade your alternator or install a stiffening cap.

Whether it’s better to use one multi-channel amp or multiple amps to power your various speakers depends on factors like the amount of available space, the results you’re looking for, the amplifier classes you use, and personal preference.

The most common reason to wire in multiple amps is to have one for your main speakers and a second amplifier for a subwoofer.

If you decide to go with multiple amps, the process of multi-amp wiring is similar to single amp setups. You have a couple of options, but it’s important to take the increased current draw into account in any case.

Multiple Amp Wiring

Regardless of the number of power amps you use in your car audio system, you must stick to wiring best practices.

In terms of amp wiring, that means getting your power straight from the battery. With that in mind, you can either run separate power cables for each amp or a single cable that feeds all of them. Depending on your particular setup, either one of these options may work out for the best.

In most cases, a single power cable is the most elegant solution. If you decide to go with that option, it’s good to use the thickest gauge power cable that will work in your application.

Because your power cable needs to handle the current draw from all of your amps at once, it needs to be significantly larger in gauge than what your individual amps specs outline. For instance, if an eight gauge cable is sufficient for your amps, you may want to use a four gauge cable to run to the battery.

The best way to wire multiple amps to a single power cable is to use a power distribution block. That allows you to use a single cable for most of the run, including the crucial portion that passes through the firewall, and then use shorter individual cables to connect to each amplifier. A distribution block can also be fused, which is helpful if your amps don’t include built-in fuses.

Amp Ground Wiring

Rather than grounding your amps individually, you should also use a distribution block to provide the ground connection.

In a mirror image of the power distribution block, you should connect the individual amps to the ground distribution block, which should be connected to a good chassis ground. You can use the same ground block for your other audio components, which is also a good way to avoid ground loop issues.

Multiple Amp Remote Turn-on Wiring

In some cases, you may find that a single remote turn-on lead cannot handle the current draw demanded by multiple amps. One way to work around this issue is to connect the turn-on leads from your amps to a relay triggered by your head unit.

Wiring suggestion for two amps with a relay for the remote turn-on

Rather than receiving power from the head unit, the relay should be hooked up to another battery voltage source — either from the fuse box or directly from the battery. That will effectively isolate the turn-on signal from the head unit from the multiple amps, hopefully allowing you to avoid any issues with current overload.

Amp Wiring: Head Unit and Speakers

The way you wire your head unit to your amp will depend on the outputs on your head unit. If your head unit has multiple preamp outputs, you can connect each set of outputs directly to one of your amps.

If your head unit doesn't have multiple preamp outputs, you’ll have to check your amps. In some cases, internal amp wiring includes preamp pass-through functionality, allowing you to connect multiple amps. In that case, you can connect the pass-through outputs on your first amp to the preamp inputs on your second amplifier, and so on.

If your head unit doesn’t have multiple preamp outputs and your amps don’t have pass-through functionality, you’ll need to use Y adapters to split the signal between your amps.

The amp wiring situation can be more complicated if your head unit doesn’t have any preamp outputs. You’ll use speaker wire to connect your head unit to your amps, and you’ll either need power amps with speaker-level inputs or a line output converter to provide you with line-level inputs for your amps.

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