How-to guide

How To Hook Up A 4 Channel Amp To Front And Rear Speakers

Adding a 4 channel amp is a great idea. I’ve enjoyed powerful, crystal-clear sound in my vehicles for years using my own 4 channel amps.

But how do you hook them up?

In this guide I’ll show you how to hook up a 4 channel amp to front and rear speakers. After installing hundreds of amps in vehicles just like yours I’ll share with you the fundamental tips you need for great results.

And hey – don’t worry…in most cases you can do it yourself and get professional results on a budget!

Contents

Infographic – How to hook up a 4 channel amp (tips and general guide)

Hook up amp 4 channel amp front rear speakers infographic diagram


Basics first

If you’re reading this there’s a good chance you’re not familiar with installing an amp, connecting wiring, and other details related to hooking up a 4 channel amp in a vehicle.

Not everyone has installed car stereo equipment before so I’m going to be as thorough as possible and avoid making any assumptions about how much you know.

What is a 4 channel amp?

Holding Alpine MRV-F300 amp in my hand

Today’s 4 channel amps offer newer technology, better sound, and more compact size than in the old days. An excellent example is the Alpine MRV-F300 50W x 4 model. It uses Class D technology to run extremely cool and yet it’s small enough to fit under a car or truck seat. Very nice!

What a 4 channel car amplifier is may seem obvious at first but there’s a bit more to know Additionally, there are some interesting (and good) ways they differ from 2-channel amps.

In fact, there are actually a few benefits you’ll get using one 4 channel amp instead of 2 stereo ones to power your front and rear speakers.

A 4 channel amplifier is a stereo amplifier with 2 more channels built in to boost (amplify) weak input signals to a higher voltage signal. This drives speaker voice coils to move the speaker cone and produce sound.

4 channel amplifiers add more channels into a more compact and efficient design than separate amplifiers would have.

Additionally, they offer more flexibility, as most can be configured for “bridged” operation which can gives more power when you don’t need all 4 channels.

What is “bridging” an amp?

Bridged mode capability is a special design feature in which a “push-pull” set up is created: one channel (normally used for the left speaker) produces a signal that’s the opposite of the second channel (normally used for the right speaker).

This causes the speaker to receive a voltage audio waveform that is the difference of the two channels – resulting in more available power to speakers.

Essentially, bridged mode is a flexible way to get more power if you’re not driving 4 speakers. It means 2 channels are sharing the workload of one speaker between them and therefore and drive it with more power.

2 channel vs 4 channel amp diagram

2 channel vs 4 channel amp diagram

A 4 channel car amp is basically an expanded version of a 2-channel amp. However, because they’re built together and not 2 separate 2-channel amps, they’re more compact. This saves installation space and makes it easier too. Additionally, most can be bridged to use 2 channels (or 3, depending on your needs) so you’re not restricted to using them with only 4 speakers.

The benefits of using an amp to drive speakers

Whether you have a factory stereo or a great aftermarket (non-factory) one, adding an amplifier is one of the best decisions you can make.

In-dash stereos are very limited in how much power they can produce. They can’tt drive speakers with the same clarity and low distortion like a good amplifier can.

The maximum volume you’ll be able to get from your speakers will be pretty low, too.

There’s simply no way around it – most in-dash stereos are limited to about 15W-18W RMS of power for each speaker channel. That’s because they’re running directly from the +12V supply. Amplifiers are unique in that they take the +12V electrical supply and boost it to a higher voltage.

When a signal is boosted and sent out to your car’s speakers the voltage is much higher and the speaker can receive much more power.

That’s why tiny amplifiers are rarely worth bothering with – if there’s no special power supply inside, it’s simply not capable of producing much power.

Getting great sound

Powering speakers from an amp makes a big difference, and I’ve enjoyed excellent sound for years this way.

When an amplifier drives your vehicle’s speakers it’s often not even pushed to its limits. The sound produced at the speaker has lower distortion, doesn’t “bottom out” when heavy bass is played, and you can get a lot more volume, too!

Additionally, using an amplifier with built-in high-pass crossovers means you can block out lower-end bass that causes your speakers to distort and attempt to play music tones they’re not suited for.

The result is cleaner sound, less distortion, and great volume – you can crank your music even higher!

Just imagine driving down the road with the windows open and finally being able to blast the music you love. I’m confident you’ll love it as much as I do.

Things you’ll need

Image of a paper checklist being prepared with a marker

It only takes a few minutes to make a list of the parts, wire, tools, and other bits and pieces you’ll need. Planning ahead can mean the difference between getting your system going without major problems or having a frustrating time – or complete failure! I always get organized and get my items together before I start a job.

Planning ahead is very important. You don’t want to run out of wire or discover you don’t have the rights parts, for example. That will mean you can’t finish your project.

It’s even worse when you have to drive around town searching for items or you’re not able to do anything after the stores close. Believe me, I’ve been there, and it’s terrible!

Notes about wire, tools, and a few other things

When it comes to installations, always plan to have more, rather than not enough, wire. This goes for speaker wire as well as RCA cables.

The amplifier kits I recommend have the right length for your amp installation, but speaker wire & RCA cables are another matter in this case.

What length and size speaker wire do I need?

wire of 16 ga speaker wire

There’s no need to spend an excessive amount of money on speaker wire. 18 gauge is enough for many installations, but 16 gauge is a great choice too, if the price is right. A great example is this AmazonBasics 100 foot roll. I recommend a 100 foot roll for many installations with a 4 channel amp (see why below).

Here’s an estimate of the worst-case scenario for the length of speaker wire required. I’ll use the example of installing an amp using speaker-level inputs, with the following typical installation:

  • Amp is located in the trunk
  • Speaker level signal connections near the radio (center console)
Let’s use roughly a 15′ length of distance from the radio to the amp. That’s a good estimate in my experience.

So we have:

  • Wire from radio to amp (signal wire): 4 channels x 15′ = 60 feet
  • Wire from amp to speaker wiring near radio: 4 channels x 15′ = 60 feet

Total estimated wire required: 120 feet.

That means you need 2 100 ft rolls of wire. Or at the least, 1 100 ft roll and 1 50 ft roll. If you’re planning to use a line-level adapter, expect to pick up a 100′ roll.

If your installation is using RCA jacks, expect a 100 ft roll also (4 channels x 15′ length estimate for the speaker wire from the amp).

What about RCA cables?

KNU Conceptz KCA-K4 4 gauge amp wiring kit RCA cables imageIf you’re installing a 4 channel amplifier and using RCA cable connections, you’ll need to buy a 2nd pair along with your amp wiring kit, as most only include a 2-channel cable.

For most installations I recommend 18′ length cables. That’s usually long enough for most vehicles and you should usually have enough length to hide the cables inside the interior and under the rear seat, etc.

There’s no reason to spend an excessive amount of money. Just pick up some good quality, well made cables. Even a pair like these value-priced ones will be fine in most cases.

Tools you’ll need.

Image showing example crimp tool and crimp connectorsCrimp tools are great for installing your amp and speaker wiring with professional results. If you’re doing your own installation, you can get by with an inexpensive tool like this Pros'Kit crimp tool. Crimp connectors are sold separately in many automotive parts stores or general stores and are very affordable.

I recommend a few tools. If you shop carefully, you can avoid getting ripped off on tool prices. When connecting speaker wiring to factory wiring, it’s easier to use crimp connectors than solder.

Never simply twist wire together and wrap it in electrical tape. Always use a reliable connection.

During warm weather electrical tape adhesive can fail and the tape can come off of wire. This exposes it to possible short circuits and potential damage to your radio or amp.

If you have access to a cordless drill, that’s fantastic! They’re great for drilling holes in the vehicle’s metal for mounting your amplifier or connecting the ground wire to bare metal.

I also recommend the following:

  • Wire cutters (some crimp tools have this built-in)
  • Roll of quality electrical tape
  • Wire ties (“zip ties”), 6″ length, bag of 100
  • A digital test meter for voltage measurement

Etekcity MSR-R500 digital test meter example

A test meter is often incredibly helpful when installing an amplifier. However, you don’t need to spend much money! A basic but good budget model like this one at Amazon will work great.

I recommend getting an affordable but good digital test meter to find a switched +12V wire for getting a remote-on signal to the amp.

They’re also extremely helpful when troubleshooting power problems when something isn’t working.

Shopping lists

Here’s a general but pretty accurate list of what you’ll need for connecting a 4 channel amp to front and rear speakers.

Installation types 1 or 2: Factory radio or no RCA connections

  1. 4 channel amplifier with speaker level inputs or amp and line-level adapter
  2. 120 feet or more speaker wire, 18 gauge or larger
  3. Amp wiring kit
  4. Crimp tool and butt (wire crimp) connectors (25 or more at least)
  5. Cutting pliers
  6. Electrical tape
  7. Wire ties, 6″, bag of 100
  8. Test meter

Installation type 3: RCA connections

  1. 4 channel amplifier with speaker level inputs or amp and line-level adapter
  2. 100 feet roll speaker wire, 18 gauge or larger
  3. Amp wiring kit
  4. Additional RCA cables, 18′ minimum
  5. Crimp tool and butt (wire crimp) connectors (25 or more at least)
  6. Cutting pliers
  7. Electrical tape
  8. Wire ties, 6″, bag of 100
  9. Test meter

Be sure to plan well and estimate the amount of speaker wire you’ll need. For the amp installation itself I strongly recommend using a pre-made amp wiring kit like you’ll find here in my amp kit buyer’s guide.

You’ll also need to get a 2nd pair of RCA cables. I recommend 18 ft length or more. Don’t spend too much money, but do get decent quality ones.

How to get a signal to your amp

Image of an aftermarket car stereo outputs labeled

Image of an aftermarket (non-factory) stereo showing the RCA jacks and speaker output wiring. Either one can be used for getting a signal to an amp, but RCA jacks offer a better option. They’re normally lower distortion and allow using plug-in RCA cables. If those aren’t available, either an amp with speaker-level inputs or a line level (speaker level) adapter can be used.

In order to install a 4 channel amp and drive all 4 speakers, in many cases the biggest obstacle is getting a signal to the amp. Once that’s done, the rest is usually a standard amp installation.

There are 3 basic ways to get a signal to your 4 channel amplifier:

  1. Connect speaker outputs to your amp’s speaker level inputs
  2. Connect a line-level adapter to the radio then use RCA cables to the amp
  3. Connect your radio to the amp using RCA cables directly
NOTE: I won’t be covering factory sound systems that are “premium” and have a factory amplifier. Those such as Bose, JBL, and Mark Levinson, often found in luxury vehicles or special-edition models, are much more complex and harder to deal with.

In that case my advice is to speak with a good installation shop first and do your research.

If you feel that factory amplified systems should be here as well, send me a message or comment and let me know.

In a few cases adapters are available to connect an amp to a factory amplified system’s audio wiring, but it’s often difficult or there are obstacles you won’t find until you get started.

One of the reasons why is that factory amplified systems often have non-standard wiring connections for the audio path and are prone to bad noise problems if you connect an amplifier without the proper adapter or wiring.

Which type of connection do I need?

If you have a radio with RCA jacks, skip on down to the next section.

However, if you have a stereo with no RCA jacks (which is always the case for factory-installed stereos) you’ll have to buy one of the following:

  • A “line level” converter
  • An amplifier with speaker-level (“high level”) inputs

1. Line level converters

PAC LP7-4 4 channel line level converter

Line-level converters like this PAC LP7-4 4-channel model are designed to take speaker-outputs from a stereo with no RCA jacks and adapt them to RCA jacks. Using this, you can run RCA cables to your amplifier.

Line level converters are designed to allow connecting to an amplifier’s RCA inputs by converting speaker outputs from a stereo to a low-level signal an amp can use.

It’s very important to buy a quality, well-designed line-level adapter for avoid noise, poor sound quality, and other problems. Don’t get the cheapest – instead, get a name brand model you can rely one (like the one above).

2. Speaker level inputs

Car amplifier speaker level input example
Amplifiers with high-level (speaker-level) inputs like this one allow connecting to speaker wiring for a signal source. This avoids having to buy a separate adapter.

Speaker level inputs are common on many 4 channel amplifiers. These amps contain electronics that scale down speaker wiring signals to a lower signal safe for the amplifier’s input circuitry.

They’re simple to connect: normally it’s just a matter of connecting both positive (+) and negative (-) wiring for each speaker channel on a small wiring harness included. This then plugs into the speaker level input connector.

4 channel amp speaker level harness example

A typical speaker-level input harness for a 4 channel amp. The wires are color coded to make installation easier. White = left front, gray = right front, green = left rear, and purple = right rear.

While it can save money (you won’t need a line-level adapter in this case) I often recommend that people consider buying a line-level converter anyway.

This allows an easier upgrade for your stereo later, which is very common for people to do. Using the line-level converter now will allow you to run RCA cables to your 4 channel amp to be used later if you buy a better stereo (which will include RCA jacks, almost always).

3. RCA jack (line-level) connections

RCA jacks offer a clean, lower-noise connection than speaker-level adapters do, but honestly it’s not noticeable to the average person. RCA cables (line-level connections) are the preferred way to connect a signal to your amp if you have that option.

RCA jacks on the rear of a Pioneer head unit. This is the ideal way to connect your amplifier’s signal inputs, if available. For a 4 channel amplifier you’ll need 2 stereo RCA cables to do so. White represents the left channel white red represents the right. These are standard colors for audio outputs for both car and home stereo.

If your stereo has RCA jacks, then congratulations. Things just got a bit easier – and potentially better sounding, too!

You’ll need 2 stereo RCA male-to-male cables (4 audio channels total) to run from the radio to your 4 channel amp. That’s 4 signal channels: left & right front and left & right rear.

4 channel amp signal connection diagram

Here’s a helpful diagram showing the most common connections you’ll need to make one of the 3 most common cases I mentioned earlier:

  1. Connecting to your amp’s speaker level inputs
  2. Using a line-level converter
  3. Connecting your amp to the radio’s RCA jacks

4 channel amp signal connection diagram

You can also click here to view the .pdf document for print or download.


Connecting and running signal wiring

Speaker-level connections

As mentioned above and as shown in the diagrams, if you’re using speaker-level outputs to get a signal from the radio, you’ll need to connect wire. Ideally you’ll do so near close to the radio, then run the wire together as a bundle.

You can bundle speaker wire together with wire ties to keep it neat and make the installation easier.

Estimate the length of speaker wire you need to reach the amp (or line level converter) for each audio channel. To do so, run a length of wire from the radio to where the amp will be installed, then allow a little extra and enough length to run around curves and interior part.

Cut 7 more lengths of wire, for a total of 8:

  • 4 channels (4 pairs of wire) going to the amp’s speaker level inputs
  • 4 channels from the amp to the radio’s factory speaker wiring

Image of car stereo wires crimped

I recommend connecting to speaker-level outputs using crimp connectors and a crimp tool for a reliable, solid connection. Blue connectors are normally the right size for 18-16 gauge wire.

Factory stereo color codes

If you have a factory stereo, you’ll need to find the wiring colors for find the speaker wiring.

A great resource for that is The12Volt.com, where you’ll find wiring diagrams for your vehicle and color codes listed.

Making connections

Image of factory stereo wiring harness

After removing the radio you’ll find connectors like this for the factory stereo wiring harness. You’ll need to separate the speaker wires, cut them, and attach wiring to run to the amp.

Remove the radio and disconnect the factory wiring plugs or aftermarket radio’s wiring harness.

Cut the speaker wires, leaving enough length to move the wire and to have enough length to connect to the wire freely.

Strip a small part on both the stereo’s speaker wire and your amp speaker wiring. If using a line-level adapter, connect to the stereo’s speaker output side. Then connect the 4 pairs of wire to the speaker wiring in the harness.

Insert the stripped wire (about 1/4″ of bare wire) into the connectors and crimp them carefully using a crimp tool if you have one. Alternately, you can twist together wire, solder it, and carefully wrap it with electrical tape or use heat shrink tubing for insulation.

If using speaker level inputs on your amp, also connect 4 pairs of wire to the output of the stereo.

Wire bundle with zip ties example

To make a neater, more professional installation, bundle the speaker wiring similar to this using wire (“zip”) ties. I recommend using 6″ ties which often are sold in packs of 100.

Once all wiring is connected, bundle it up using wire ties or, optionally, a little bit of electrical tape wrapped around. In both cases spacing out wire ties or tape about ever 1 or 1.5 along the length of the wire works well.

Connecting RCA cables

Example of connecting RCA cables to rear of a car stereo

Connecting RCA cables to an aftermarket (non-original) stereo for running to an amplifier.

If you’re using a line-level converter or have a stereo with RCA jacks, connect all 4 cables plugs to the front and rear outputs.

RCA cables are sometimes marked with left and right symbols (“L” and “R”). In some cases, white, clear, or some lighter color can be used to represent the left channel.

Connect the cables consistently so you’ll be able to recognize which one is which. If the front and rear RCA cables are the same, you might want to mark front and rear using some masking tape and a marker or pen.

Connect the remote-on amp wire

Don’t forget the remote wire! Amp wiring kits include a small wire that’s used to connect the amp so that it switches on and off with the accessory position of the ignition switch.

Locate a +12V wire that has power when the ignition is switched to “ACC” or similar, but turns off with the key. You may also have good luck finding an existing wire color from vehicle wiring diagrams I mentioned earlier or from a Google search.

I recommend checking the wiring even if you have already located it online, just to be sure.

Before re-installing the radio connect this wire and run it along side the speaker wiring.

How to connect a 2 ch. car stereo to a 4 channel amp

Diagram showing a 2 channel car stereo connected to a 4 channel amp

You can connect a head unit car stereo with only 2 channels (left and right) to a 4 channel amp easily. Ordinarily all you need is 2 RCA Y adapter cables. The head unit’s left channel RCA jack should be connected to the left front and left rear amp inputs. Likewise for the right channel. If using speaker level inputs on the amp, use the connections shown above. NOTE: Use only ONE of the two connections above! Never connect both types at the same time! Speaker-level outputs will damage RCA connections.

If your head unit (car stereo) only has 2 RCA jacks or two pairs of speaker outputs, that’s not a problem.

As shown in the above diagram, you can connect 2 channels to a 4 channel amp using either the speaker level inputs wired in parallel or by using simple RCA adapter cables.

RCA y adapter cable image

All you need is a decent pair (a total of 2) female to male RCA “Y” adapters like these low-cost ones from Amazon.

The sound quality will be exactly the same. Today’s amps are designed in such a way that there’s no harm in using a Y adapter to connect the amp. The amplifier will receive exactly the same signal, with the same quality, in the front channels as well as the rear.

The only drawback is there won’t be a front to rear fader control like with head units with 4 channels of outputs.

After connecting the stereo to the amp, you’ll need to adjust the rear gain to set the volume level for the rear speakers as needed for the proper volume depending on the stereo’s signal strength.

Installing the amp

Product image of Belva BAK82 amp wiring kitAn amp wiring kit like this one will make installing your 4 channel amp much easier. A good-quality one like this Belva 8-gauge complete kit includes not just wiring but much more. You’ll also need to pick up a 2nd pair of RCA cables (if using them) and enough speaker wire.

Your amplifier needs a good solid metal connection to ground and you’ll need to run the positive battery wire to the engine compartment. Your amp wiring kit will also include a fuse holder that should be installed near the battery as well (most kits include instructions, by the way).

You’ll also need to connect the amp’s speaker outputs to the wire you ran from the radio.

As it also applies to 4 channels amps, for the amplifier installation you can follow my guides here:

Here’s a basic diagram as well to help:

How to install a 4 channel amp diagram

Setting up your amp

Alpine MRV-F300 4 channel amp end viewOnce installed, you should set up your amp’s gain levels and crossovers for best sound. In this image you can see the adjustable crossovers for both front and rear channels. Turn on the high-pass crossovers and adjust to a setting close to 50-60Hz, to allow good bass for music but block low-end bass that distorts.

Once installed, you’ll need to set up your amp’s gain levels and crossovers, if available. Most sold today have that. (See my recommendations at the end for some great models)

Gain control is the amount of signal amplification the amplifier performs. Ideally, with a good input signal it can be kept low to reduce any hiss or noise that can appear when it’s turned up high.

Here’s a great rule of thumb for how to adjust the gain for this type of system:

  1. Turn down gain controls on the amp
  2. Turn the stereo’s volume to 2/3 of maximum
  3. Slowly raise the gain controls until the volume is enough

When finished you should have enough volume available from the stereo but noise should be minimal. You’ll still need to tweak it a bit if volume is too high or too low.

Setting the crossover

As I mentioned at the beginning of this guide, using high-pass crossovers will allow more volume with less distortion and will help protect the speakers from heavy bass.

For both front and rear channels turn on the high-pass feature and, if an adjustable dial is available, set it near 50 to 60Hz. Some models don’t offer an adjustable frequency for the cutoff, but are likely preset to a good level.

Test and tweak

Once installed, test and tweak your amplifier as needed. A great way to mount your 4 channel amp is by using a board mounted to the car, covered with speaker box carpet or other material.

Play some music you’re very familiar with and adjust things like bass, treble, and the fader as needed. Using music you’re very familiar with (of high quality) means you’ll be able to notice any problems with the sound fairly easily.

If you don’t already have one, you might consider later upgrading to a head unit with built-in equalizer (EQ) functions to help tailor the sound.

Summary and recommended products

Hopefully you’ve found this post helpful. Hooking up a 4 channel amp to your front and rear speakers takes some work and time, but it’s a great way to get sound you’ll love.

Considering buying an amplifier? You can find some great 4 channel amps (including the Alpine MRV-F300 pictured here) in my 4 channel amp buyer’s guide.

You’ll also need a good amp wiring kit – I’ve got a good amp kit buyer’s guide here.

If you find anything missing or have suggestions, just leave a comment below or send me a message!

22 Comments
  1. Thanks for your great write up. I only have 1 pair of rca outputs on my HU. Can I just use 2 pairs of y splitters to send the RCA signal to 4 channels or will I lose some quality?

    • Hi there, Taylor! I appreciate your comment and the question, too. It’s a good question!

      Yes, you can use 2 Y RCA cable adapters to send 2 RCA outputs from the head unit to 4 inputs on an amp. The amp is designed in a way that it won’t matter, and it won’t hurt anything.

      The signal quality should be basically exactly the same (unchanged) for all 4 inputs to the amp.

      You’ll just need to use the gain on channels 3 & 4 to set it like a fader when getting it set up. I would set the front pair first correctly and then worry about setting the rear channel levels.

      Thanks!
      Marty

  2. So going off what you’re saying it seems like you run your speaker wire out put from amp back to behind stereo and then connect the to the wire harness which then is using the stock factory speaker wire to feed the speakers in doors. Do you find any difference in avoiding the factory speaker wires to speakers? Meaning run new speaker wire from amp directly to each speaker. I was going to run with 16g this way, directly from amp to each speaker. If I do it your way and run from amp to behind head unit and use the factory wire from behind head unit to speakers will I lose any sound quality or power?

    I’m not sure what size the factory speaker wire is running throughout the vehicle.

    Installing in a 2001 Ford ranger XLT extended cab

    Here’s my product information-
    -I’m using two sets of RCA
    – 4 guage power supply
    -Jbl GX862 speakers
    -Jbl GX-a604 amp
    -Pioneer DEH-6000BT head unit

    • Recently installed a pioneer avh 211ex as well as all new speakers to a 4 channel amp wired with rca cables. We’ve tried everything and can’t get any sound to the speakers anything we’re missing? If you need more info let me know. All help is appreciated.

      • Hi Miller. As some details are missing, I’m assuming you’re trying to set up a system like the following:

        AVH 211EX -> [RCA cables] -> Amp -> speakers (directly wired). If that’s not the case please let me know.

        I would verify the amp is working ok by using a test speaker wired to it directly and also connect your phone or other audio source directly with a headphone to RCA cable adapter. That way you can be 100% the amplifier is fine.

        If that works, then connect the AVH211EX to another amp or home stereo (outside the vehicle) to verify the RCA signals are working. They should be, as that’s not a problem I’ve seen much.

        Also, be sure to make sure that audio outputs aren’t disabled in the menu settings. Check your manual. Some head units offer the option to turn off the speaker outputs or RCA outputs.

        Are you using the speaker outputs?

        What we would normally do in a case like this is do a “bench test”: Remove the stereo and amp and test each one separately with a separate ratio or speaker we know for sure works to see which one isn’t working as expected.

        Without more details those are my best suggestions.

        Good luck!

        Marty

    • Hello, Chris! Thanks for visiting the site & for the comment.

      Usually factory speaker wiring is around 18-20 gauge or so, which is fine for this kind of system. Yep, you can just run the speaker wire from the amp to the factory wiring. Ideally you can use a harness adapter to avoid having to cut the factory wiring.

      In this case you won’t lose any sound quality or power. It’s when you get to much higher power ranges that it makes a difference.

      That looks like some nice items you’ve picked up so I’m sure you’ll enjoy them. One comment I do have is that the 4 gauge power supply is larger than you need for that amp. If it’s not already installed and you haven’t run the wire yet, I’d use 8 gauge.

      That’s a bit easier to deal with especially when going through the firewall. Also, 4 ga. wire may not fit well on the power terminals on that amp.

      I hope this helps!

      Marty

  3. Great info!
    I have a mrv-v500 5 channel amp hooked up and 2 subs. I’m using a jl fix 86 processor because I did not want to change my head unit so I kept it factory. If I want to change my head unit, using the rca out puts from head unit to amp is my best choose right? Also I’m guessing I would have to remove the processor since it would be a aftermarket head unit.

    • Hello, Julio! Glad to hear from you. I’m glad you like the content.

      Yes, if you change the head unit, using the RCA connections would deliver the best sound. However, the good news is that you won’t need to get rid of the FiX-86. It will accept a wide range of input levels and should work with RCA (line-level) inputs.

      However, you’ll need to use some RCA to bare wire adapters or cut cables to connect it, according to what I saw in the owner’s manual. There should be some items you can find that will do the trick.

      If you can’t find any let me know and I’ll look one up for you.

  4. Hi, i have pair of focal 165 vrs (60rms) running through hertz he-4 (75watts rms x 4 at 4 ohm) and the speakers sounds bad no bass. I have connected them on channel A and have sub on channel b bridged. Any idea why they dont sound good. What possible i have done wrong ? Btw i run 16g wire from amp to front hu wiring harness then using factory wiring. (Audi a3 8p). Thanks!

    • Hi Pawel. You don’t mention what stereo you’re using and a few other details like that, so I’ll answer the best I can based on what you wrote.

      1. Are you using the high-pass crossover function on the front speakers? If so, switch it off and see the result.

      2. How did the factory speakers sound? Was there good bass for those? If yes, that leads me to believe it’s either installation related or the speakers won’t perform well in the doors as they are now.

      3. You need to be 100% sure that there’s nothing in the factory speaker wiring that could be causing an issue. To verify this, temporarily use some speaker wire to bypass the factory wiring you’re currently using. If that changes the sound, there’s likely some type of crossover component in the factory system causing the problem.

      Unfortunately, not all speakers will sound good in all car doors. If there’s not a decent enclosure (if there are bad air leaks, etc) poor bass happens. In that case it’s installation-related and you’ll need to try to seal off the doors where the speakers are installed.

      Don’t worry about the speaker wiring size – that’s not going to cause poor bass response.

      Hopefully this helps. 🙂

  5. Nice site – I’ve got a related but slightly different question that you may be able to address. I have a 4 channel amp (JBL GX-A604 435W) that I haven’t connected yet, a total of four JBL Stadium GTO 620 speakers in the doors, and a pair of JBL Stadium GTO 750T tweeters in the dash, for a total of six speakers. I’m currently using the factory wiring with an aftermarket head unit and everything sounds OK.

    This is a temporary situation – I bought the amp with the intention of running new speaker wire and RCA cables for signal and connecting all the speakers. Easy enough, right? I had planned on just hooking up the two front door speakers to the tweeters in parallel (two channels) and then hooking up the rear door speakers to the other two channels.

    The problem is that all six speakers are 2ohm, and while the amp is also 2ohm, it’s my understanding that connecting in parallel would drop that down to a total of 1 ohm, or wiring in series (which is a bit more complicated in tight spaces) would increase it to 4ohm and may reduce sound. Am I overthinking this or is this a problem?

    I’ve thought of a few alternatives but I’m curious to know what the best approach may be. One idea I had was to just leave the dash tweeters on the factory wiring and let them get a signal / power that way, while using the RCA output to the amp to drive the four door speakers on each of the four signals. Not sure if that would even work, or if it would introduce problems with delay or something else. What’s the best approach to get the most sound out of the 6 speakers? Thanks!

    • Hi MJ and thanks for dropping by! I took a look at your speakers & etc. (thanks for providing enough detail, it makes a huge difference!)

      So there’s not a “perfect” way to approach this, but I can think of 2 solutions at this moment. As you might expect, both have pros and cons. And to answer your question, yes using speakers in parallel does drop the total speaker load the amp will see. It will be 2 ohms/2 in this case, or about 1 ohm, which is too low for an amp.

      Here are 2 ideas:

      1. You can use both the tweeters and the GTO 620 speakers on the front channels by adding inline (series) power resistors, 1 per speaker. By doing so you’ll be able to raise each speaker’s total impedance load (resistance) to 4 ohms. Therefore if we do this for both the tweeter and GTO620 speaker on each channel, when wired in parallel the amp will get a safe 2 ohms load.

      You can see an example of the wiring set up in section #3 in my wiring diagram here: Wiring diagram for adding inline resistors for adding more speakers safely.

      In this case you’ll 1.5 ohm resistors with a 35W (or higher) rating. You’ll need 4 total. The trade off here is that while it lets you use 4 speakers on the front 2 amp channels, the resistors will consume a good portion of the available power. So it’s wasting power, basically.

      2. (Ideal solution) You could get a 2nd amplifier just for the additional 2 GTO 620 speakers. There are many good budget 2 channel amps that would be great for this. While it’s not always fun wiring a 2nd amp, you’ll get more control over the gain/volume for the tweeters and front speakers by using the JBL just for them, then use the 2nd small amp for the rear speakers.

      Note: While you can use the tweeters directly from the head unit, the power output & volume after a certain point won’t match that of the amp. Head units are very limited in power they can provide (15-18W usually). There won’t be an issue with delay, though.

      You could use a very compact class D 2 or 4-channel amp for the rear speakers for example. If it were me, for the best sound quality and ability to adjust the sound I’d go with option #2.

      My advice would be if you’re strongly considering using the tweeters with the factory wiring, try that temporarily to see what you think.

      Then go with one of the other 2 options if that doesn’t make you happy. Personally I would use #2 from the get-go as it’s a sure thing.

      I hope this helps! 🙂

      • Thanks, big help! If you can drop a few links for compact amps that would pair well I’d be happy to click through.

        That sounds reasonable if I can fit everything – I’ve got a compact sub under the passenger seat so I’m trying to fit anything under the driver’s, space is limited.

        I’m assuming I’d need to re-run something like a 0/1 power cable from the battery to the block and split it out via distribution block to three 8 gauge power cables for the existing amps, and then find a single ground point to tie in all three… And the grounding is another question. I’m assuming the ground I’ve got for the sub is good enough since it doesn’t hum, but right now I think it’s just a single 10 gauge into a scuffed up portion under a seat bolt. Think I’d need to use a distribution block for the grounds too, or can stuff like this be grounded individually in a car without too much worry for ground loop noise?

        Again, very happy to take any links if you have recommendations. I’m thinking I’ll end up having to pull out both front seats this time after all.

        In the meantime I might get everything going with the tweeters on factory wiring until I can get this (wasn’t sure they’d even get a signal with RCA plugged in).

        Also, I found that with my car (Impreza) I can run cables through the rubber door boots without disconnecting anything but trim, by using a heavy duty 3 foot long zip tie with the tip bent up slightly like a ski and the other end snipped off, and a little windex for lube. MUCH faster technique than most guides I’ve read.

        Thanks!

        • Hi MJ. Sorry for the delay as I was having Wi-Fi problems last night. There’s a lot to cover here so I’ll try to keep it organized.

          1. Here are 2 very good amps that are both good values and compact:

          Alpine MRV-F300 4 channel amp (bridgeable). It’s fairly compact, and sounds very good. It’s also just a good value.
          Alpine KTP-455U micro amp 4 ch./bridgeable. This is a super-compact amp (a tiny 7-7/8″W x 1-1/2″H x 2-9/16″D) and can fit in a LOT of small spaces. It’s 45W x 4 or 90W x 2 & also has a high-pass crossover option.

          The KTP-455U won’t need very large power wire so that’s another plus. Both amps are class D so they’re around 84% efficient and won’t draw as much current/you can use a smaller wire gauge typically.

          2. Yes, ideally it’s best to at least ground the amps to a single point, although even if you try to do things “perfectly” you can still get ground loop noise. It happens.

          I would say since you’re going to use distribution blocks anyway, just run the amps to the ground block and then out with a single ground wire to a good ground point such as:

          • Seatbelt bolt location (brass/finished bare metal bolt to the body)
          • Another clean metal bolt or screw on the body
          • By using a self-tapping metal screw and cordless drill (my preferred option as it’s fast, easy, and works basically 100% of the time). This also lets you find many places closer which is important if the ground wire is short. Often times many in wiring kits are 3-5 ft long etc.

          In all cases I would use a good quality crimp ring terminal on the ground wire. Amp wiring kits include these and make installation a lot easier.

          3. You won’t need to spend a ton on wire or terminal blocks. In your case I think you’d be fine using 4 or 2 gauge in and 8 gauge out.

          You can do it this way to save costs:

          • Get a good quality amp kit like this one, to run to the dist. blocks: KnuConceptz 4 gauge kit
          • Get enough additional power, ground, and remote wire to go each amp. You can buy this by the foot or on rolls reasonably priced.
          • Some good quality/good value dist blocks are these here: InstallGear 4/8/10 ga. blocks

          4. That’s a good idea about running your wire in the doors! Good thinking. You can also straighten a thin coat hanger and bend the end in a round loop so it won’t snag and use that, too. 🙂

          Have a good Saturday!

  6. I have a Sony MEX N4200BT so do I run the rca cables from the radio to the amp and use some speaker wire from the speakers that’s in the doors to the amp? I ran the power from the cars batter to the amp and the ground from the chassis of the car to the amp just wanted to know about the speakers and I got the remote turn on wire ran from the aftermarket deck to the amp just was wondering how do I get the speakers to the amp because I’m new at this?

    • Hi Donzel. Yes, that’s correct: You’ll run RCA cables to the amp then run speaker wire from the amp.

      However, it’s MUCH easier to just run the speaker wire from the amp to the factory speaker wiring where the original radio was. This works if you don’t have a factory amped system.

      Usually what works best is using a stereo harness adapter to connect power for your Sony, then just connect the amp’s speaker wiring to the harness adapter’s speaker wiring (they’re labeled and color-coded so you’ll know which wire is which).

      Really it should be very straightforward in most cases. Just be sure to plan for getting enough speaker wire. I would measure the length from where you’ll put the amp to the center of the dash, then multiply x 4 to find out how much.

      Usually you’ll want to round up a bit to be sure you don’t come up short just in case.

  7. current 4 channel amps do not the list the output of the channel i.e., RF/LF, RR/LR. Besides trail and error is there anyway to know which output is driven by which input?

    • Hi Mike. That’s odd that your amp doesn’t have its outputs marked, but I’ve seen that before.

      Generally it’s inputs #1/2 = Left front, right front, and inputs #3/4 = Left rear, right rear if the RCAs are numbered. Otherwise, yes it’s trial and error if you don’t still have the owner’s manual with the speaker connection diagram in it.

  8. You have a very nice write up, very easy to understand. I was wondering if you could help me out with my situation. I have a 2006 Tahoe Z71 with Bose and Onstar. I’ve replaced the headunit with a Pioneer and the Pac Radio Pro 5 wiring harness, added two 12’s and an amp, and replaced door speakers with some NVX coaxials. Everything has been fine. However, I still wanted to add more power to the door speakers. So, I ran new speaker wire through all the doors directly from the speakers to the 4 channel amp. I add power and ground distribution blocks. After everything was finished and cut on the subs are working fine and the only speakers working are the tweeters in the A and D pillars, which I did not touch. So I’m lead to believe it must have something to do with the Bose amp or something similar. Any suggestions or places to point me in the right direction?

    • Hi Kayla & I’m glad you like the article!

      I’m not 100% clear on your installation and problem. Did you keep the Bose amp originally and replaced the door speakers…then added the 4 channel amp/wired directly to the doors later?

      The first thing I would do is to make sure the 4 channel amp is working right. If you’ve wired it directly to the new (NVX) door speakers correctly and the amp is ok, there shouldn’t be a problem.

      I would disconnect the door speaker wiring from the amp and use a test speaker right at it to check it. Also check to make 100% sure you have a good ground, +12V, and remote connection. If that’s all good then check the wiring to the speakers & make sure you get close to 4 ohms for each pair of speaker wire.

      It sounds like you’re just wanting to bypass the Bose system and drive the door speakers directly. That shouldn’t be a problem if the amp is ok and wiring is good.

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