How To Wire A Computer Power Supply To A Car Amp

How to wire a computer power supply to a car amp featured image

There’s more than one way to power a car amp in your home. Even so, computer power supplies are easy to find and make a great option – if you know how.

In my detailed guide, I’ll show you how to wire a computer power supply to a car amp. I’ve also put together some great diagrams, tips, and more to help you enjoy your music with less hassle and fewer headaches.

Contents

Can a computer power supply run a car amp? What to know

Can a computer power supply run a car amp man thinking question

Yes, it’s possible to use a PC computer power supply for powering a car amp. 

There are a few things you’ll need to know though. For example, unless you’ve got a higher-power model supply you won’t be able to drive speakers with the same power you could when installed in a car.

Do you need to hook up the remote wire on your car amp?

Yes, a car amp won’t work without a +12V signal on the remote wire terminal. The amp’s internal power supply is controlled by this wire and acts as a shutoff control. Likewise, you’ll want to either turn the power supply on & off as I’ll show you or use the remote wire as a shut off in order to keep the amp from drawing power when not in use.

Computer power supplies also have a particular control wire you’ll need to connect in order to switch the supply on as I’ll show you.

Computer power supply current (amps) & power limits

Computer power supply 12V current rating examples

Examples of the current output (amps) for a typical 200W supply and a higher-power 700W supply. The current output will limit how much power you can get from a car amp.

Computer power supplies are available in a wide range of power output options, with 1500-200 watts being very common but others as large as 700W or more can be found (although they cost a bit more). This is important to know because the current limit of a power supply will limit how much power your car amp can produce.

That means you need to be aware that for higher-power amps you can’t expect to drive speakers with the full power output it’s rated at. The good news that unlike in cars, speakers used in your home use less power for the same volume because vehicle interiors are poor for sound and require more power for good results.

How to power a car amp with a computer power supply (diagram and details)

How to wire a computer power supply to a car amp diagram

Using an ATX (desktop computer) power supply for a car amp isn’t hard – in fact, you only need a few steps:

  • Power connections: Cut the +12V wires (yellow) and the same number of ground (black) wires. Strip the insulation to leave about 3/8″ to 1/2″ bare wire. Twist them together tightly or use a crimp connector (ring terminal, spade terminal, etc) and connect to the amp’s power & ground terminals, being sure not to leave any stray wire strands sticking out to cause a short-circuit.
  • Supply on control: PC supplies don’t turn on even if the on/off switch on the case is used. PC motherboard uses a control signal to the “supply on” wire pin. To do the same, you’ll need to find, cut, and jumper this control signal wire to a ground wire either directly or with an on/off switch if you like [See diagram]
  • Amp remote wire: There are several great ways to do this and I’ll cover them below.

Once you’ve connected the +12V and ground wiring then ground the “supply on” wire the supply should start up and your car amplifier should power on. There are some cases where you could have a problem, however.

NOTE: If you’re using a high amount of current be sure to use all or nearly all of the yellow +12V wires to connect to the amp. Just like with a car amp installation, you need enough wire conductors to supply higher current without losing voltage from insufficient wiring.

A note about some amps

Larger, very high power car amplifiers can sometimes draw a short current “spike” when they’re first connected to a power source after being disconnected. That’s because they contain large capacitors that, when first connected to power, momentarily draw a huge number of amps.

When this happens it’s possible it could trip the self-protect mode in your power supply. If that happens you can try starting the supply and then wait before turning on the remote wire. You can also leave the supply running when the remote wire is disconnected so the amp’s capacitors don’t discharge when the amp is turned off.

It’s possible you may need a more robust power supply if it happens but it’s not a problem most people should run across.

Remote wire options & examples

How to connect remote wire on car amp used in home diagram

The car amp “remote” terminal uses a low-current +12V input to start its power supply & related circuits. You’ve got a few different options you can use:

  1. Jumper wire:  When connecting the power and ground 12V connections, you can use a small jumper wire from the +12V battery terminal to the remote it so it’s on any time the amp has power. 18AWG or smaller wire is fine (you don’t need a large gauge wire).
  2. Jumper wire + switch: The same as #1 but to control it yourself you can add a simple inline switch on the remote wire. This is helpful if your power supply doesn’t have an on/off switch or you’d rather leave it running.
  3. Home stereo use – RCA converter with remote lead: If you’re connecting the amp to speaker outputs on your home stereo you can use a line level converter with a remote wire output. This will turn the amp on and off automatically with the stereo’s output.

If you’re using a toggle switch on the remote wire you can leave the AC/DC power supply plugged in. When the amp’s remote wire is off (disconnected) the amp will shut off and it won’t drain power.

Using a line level converter with remote wire output

Example of line level converter with remote wire output Axxess AX-ADCT2

An example line-level converter with remote wire output. You’ll need to connect these to 12V power and ground for the internal electronics to work. When the speaker level inputs detect a signal the remote wire output will produce +12V and turn on your amplifier. When the speaker signal is lost it will switch it off automatically.

Connecting a laptop, tablet, or smartphone to the amp for audio

Diagram for how to connect audio signal to a car amp used in your home

What’s great is how many options you have for getting an audio signal to your amp’s inputs. In fact, nearly any analog (non-digital) jack can be used from almost any device. Smartphones, tablets, and laptops can be used either by their headphone jack or via Bluetooth.

Just be aware that not all headphone or audio out jacks are created the same –  some work well and have good sound & volume while others can have low volume and “meh” sound quality. However, the good news that generally speaking they’ll work well and I’ve used this approach several times with no complaints.

Connecting your smartphone or tablet via Bluetooth

You also use an affordably-priced Bluetooth receiver for around $25 from places like Amazon. They offer a direct line output jack or RCA jacks to go into a home receiver and a car amp just as easily.

Be sure to get a decent brand as the generic/no-name brand models tend to have sound quality problems and can produce odd noises between music tracks playing on your phone, for example.

What if I have a laptop with no headphone jack?

Example of a USB to headphone audio adapter

You can use a cheap USB to stereo 3.5mm adapter to get a headphone sized jack to connect an audio signal to your amp. They’re really affordable (under $10 in some cases!) and are a good option if your laptop’s headphone jack is broken or none is available.

If you’re like many people and want to enjoy music, movies, or more from your laptop there’s a problem if you don’t have a line-out or headphone jack – or if it’s just not working. A great option is to use a USB audio adapter as it’ll provide a 3.5mm jack you can connect to your amp’s RCA inputs.

I’ve found some for under $10 available with both the older USB-A and the new USB-C connection as well.

How to connect a car amp to a home stereo

How to connect a car amp to a home stereo diagram

You can also connect your car amp to your home stereo if you like. There are 3 ways to do it:

  1. Home stereo with no RCA output jacks + car amp with speaker level inputs: It’s fairly common for home stereo amps and receivers not to have RCA jacks available to connect to. If your amp has built-in speaker level inputs these can be connected to either an unused pair of speaker terminals or alongside speaker terminals in use.
  2. Home stereo with no RCA output jacks + car amp with no speaker inputs: You’ll have no choice but to use a line level converter in this case. These are car stereo adapters that you connect to speaker wiring or speaker terminals. This will drop the signal down to a level compatible with the amp’s RCA inputs.
  3. Home stereo with full range RCA output jacks + car amp: This is the easiest way but not all home stereos have full-range RCA output jacks. Some only have subwoofer RCA output jacks which are bass-only outputs. Full-range RCA output jacks can be connected directly to the car amp’s RCA inputs.

Image showing examples of line level RCA converters

Line level connectors will let you connect a car amp with no speaker inputs to any home stereo. You can connect these to unused speaker terminals on the receiver or amp as well as in parallel with home speakers already in use.

Dealing with ground loop hum (noise)

Example of an RCA ground loop isolator

You can use a ground loop isolator to break the ground conductor in RCA cables but still carry the audio signal. Since the ground connection can carry the noisy signal that gets amplified this often eliminates ground loop noise.

One thing you might not count on running into is noise. Ground loop noise, which appears as a very annoying 60Hz “hum”, is somewhat common for home stereo equipment. Unfortunately, despite car amps being designed to eliminate it, it can still happen.

One thing you can do is to try using a small gauge wire and connect it between the grounds or metal casing of the car amp, the RCA cables, and the power supply. If the noise disappears you can connect the wire to those points as a solution.

Alternatively, a ground loop isolator can often get rid of it. Connected inline with the RCA cables, they work by physically disconnecting the RCA cable’s ground connection while still sending the audio signal. They’re not expensive, but it’s a good idea to shop carefully as the “el-cheapo” units don’t always carry the entire audio range well and can cause a loss of sound quality you can notice.

Additional reading and helpful guides

Don’t go just yet! Check out some of my other great articles:

You can also browse all of my info & how-to articles here.

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How To Connect & Power A Car Amp In Your Home + Diagrams

How to power a car amp in your home featured image

It might seem puzzling at first, but it’s actually not that hard to connect and power a car amp in your home.

In this detailed guide I’ll show you how along with detailed diagrams anyone can understand.

Here’s what you’ll learn:

  • Car amp power supplies: what voltage & current ratings you need
  • How to wire a computer power supply to an amp
  • How to connect a car amp to a home stereo, smartphone or tablet, or Bluetooth
  • Additional tips to make it easier & offer more options
Contents

First facts: Can I use a car amplifier in my house?

Can I use a car amplifier in my house man thinking image

Yes, it’s possible to use a car amplifier in your house. You can also connect a car amp to any home stereo, your smartphone, and more as an audio source.

There is a catch, though. Because car amps use a different power source than home stereos the biggest problem is getting them the power they need. Not only that, but they use a remote-on wire to turn the amp on & off to avoid draining a car battery – meaning that needs to be dealt with too.

Here’s a list of what we’ll need to cover:

  • Signal inputs: Not all home stereos have RCA line-level jacks, so if you’d like to connect an amp to your home stereo it may require a workaround I’ll show you. You can also connect a car amp to nearly any smartphone or external Bluetooth receiver.
  • Power source: Unlike home stereos powered by an alternating current (AC) electrical outlet, car amps work from a +12V direct current (DC) supply. You’ll need a +12V AC-DC power supply with enough current to run the amp. Not just any AC/DC 12V adapter will do – I’ll cover this below.
  • Turning the amp on/off (remote wire): Home stereos or other audio devices don’t have a remote wire output to switch your amp on and off. However, there are some easy ways to deal with this, too.

You also need to know that:

  • Unless you have all the parts already, you may need to spend a little bit of money to get what you need & get it working. The good news is that most of it is affordable and you can even make use of some power supplies like a computer DC supply you may left over.
  • Retail stores are pretty bad about not having the parts you may need, so you might want to plan ahead and order parts online. You can find many affordably priced parts on Amazon, eBay, and from electronic part suppliers.

Choosing a power supply for car amp use

Example of how to estimate car amp current used

You can estimate how much electrical current (amperage, “amps”) your amp will draw based on its maximum power given in watts RMS. However, the truth is that’s only if you need a lot of power. For casual listening you can get by with a lot less.

Basically, there are 2 ways to go about choosing a power supply for a car amp:

  1. Getting a “good enough” power supply if you’re not driving the amp hard (fine for casual listening)
  2. Estimating the amp’s current draw based on its power rating (useful for when you want serious amp power)

Of these, #1 makes it a lot simpler. You may be able to use a DC supply you’ve already got handy or a leftover computer power supply (sometimes called an ATX power supply).

What voltage does a car amp need?

Car amps normally work off of a range of voltages, not just 12 volts, although that’s used as a general reference. In fact, as a vehicle’s engine runs the alternator charges the battery and the voltage can range from near 12V to about 14.4V. 

For home use, choose a power supply with a DC output from 12V to 13.8V, with 12V being perfectly fine to use. When shopping most of the higher-current supplies you’ll see are 12V anyhow.

At around 11V or so car amps and other car stereo equipment may shut off so it’s important to have enough voltage available.

What size power supply do I need?

Car amp DC power supply examples

Powering a car amp in home requires a power supply with a decent amp rating. Standard wall adapters won’t work as they’re very weak (0.5 to 1A, usually). You can find bigger power supplies like a 5 amp model for under $15 if you shop smart. Desktop computer ATX power supplies are cheap, easy to find, and range in power ratings up to 500W or even more.

Quick tip: Computer power supplies can offer 15 amps or even more current output making them a great solution. They’re available in a variety of power ratings such as 150W to 500W or more.  A good ATX power supply will have enough power output for the average person.

Option #1: Getting a “good enough” power supply for casual listening

When not driving an amp & speakers hard, I recommend at least a 2.5A supply for small amps (under 50W/channel). For 4 channels, I’d get a 5A or bigger. If you’d like to have more power, consider getting 15A or above.

You can find a 5A supply for under $15-$20 if you shop around. 10A and 15A supplies are fairly popular so they’re usually under $30-$35 dollars or so. When it comes to much bigger supplies that will let you drive a subwoofer with heavy bass things tend to get expensive. Very high current power supplies are around $100 and above for 30 amps or more.

However, one of the best options is to use a desktop computer power supply (“ATX” power supply) as they’re easy to find and have pretty good power output.

Option #2: Estimating amp current needed for higher power use

If you’re planning to use a car amp to drive speakers hard you’ll need a lot of amperage which you can estimate pretty closely We also need to take into account wasted power to come up with a final number. (All amps waste some power as heat and draw some additional current for that reason)

  • Class D car amplifiers are more efficient and therefore waste less power (and draw less current) than standard class A/B amps.
  • If you’re not sure what class your amp is, it’s probably class A/B. Class D amps normally say so on the amp itself, the box, or sales info. Class A/B types have been so popular for years that it’s a pretty safe assumption.

You can estimate amp current based on the maximum RMS power of the amp. Don’t use “peak” or “maximum” watt power ratings as these are misleading. We need to use the continuous power (RMS) the amp really delivers.

As class D car amps are around 85% efficient and A/B amps are around 65% or so efficient we can use that to estimate the total current an amp would need.

Class D amp example:

Estimate amps used by a 50W RMS x 4 amp:

  1. 4 x 50W = 200W total. (200W/12V) = 16.7A.
  2. Take into account power waste: 16.7A/.85 = 19.6A
Class A/B amp example:

Estimate current used by a 150W RMS x 2 amp:

  1. 2 x 150W = 300W total. (300W/12V) = 25A.
  2. Take into account power waste: 25A/.65 = 38.4A

As you see, to run a car amp at full power you’ll need a pretty big power supply! However, most people don’t so it’s usually a lot less hassle (and less money) to use one of the other supplies I showed examples of.

How to wire a computer power supply to a car amp

How to wire a computer power supply to a car amp diagram

Using an ATX (desktop computer) power supply for a car amp isn’t hard usually. It’s a matter of a few steps:

  • Power connections: Cut several ground wires (black) and +12V wires (yellow) and strip them for about 3/8″ to 1/2″ bare wire. Twist them together tightly or use a crimp connector (ring terminal, spade terminal, etc) and connect to the amp’s power & ground terminals.
  • Supply on control: PC supplies don’t automatically come on even if the side switch is on. Normally a mother board uses a control signal to the “supply on” wire pin. As shown in the diagram above, you’ll need to jumper the wire by cutting it, stripping it, and either connecting to a ground wire permanently or you can use a toggle switch.
  • Amp remote on: As there are several good options for this, I’ll cover this in more detail below. 

Once you’ve connect the supply on wire to a ground wire the power supply should start and your car amp should work. Note that in some cases, it is possible to have a problem.

Huge, high-power car amplifiers can sometimes have a short current “spike” they draw when first connected to power. In some cases, this can trip the self-protect mode in power supplies. If that happens you can try starting the supply first and then give the remote wire power after a moment.

It’s possible you may need a more robust power supply if that happens as well. This shouldn’t be an issue most of the time, though.

Remote wire options for turning the car amp on

How to connect remote wire on car amp used in home diagram

A car amp’s remote-on input uses a low-current +12V signal that starts its internal power circuitry. There are several good ways to do this:

  1. Jumper the remote on terminal:  When wiring the power and ground 12V connections, you can use a small jumper wire from the +12V terminal to the remote terminal so it’s on any time the amp has power. 18AWG or smaller wire is fine.
  2. Jumper wire + switch: Basically the same, but you can also use a simple inline switch on the remote wire to turn it on/off yourself.
  3. Home stereo use – RCA converter with remote lead: If you’re connecting an amp to speaker outputs you can use a line level converter with a built-in remote wire output. They’ll automatically turn the amp on or off with an input signal present.

If you’re using a toggle switch on the remote wire you can leave the AC/DC power supply plugged in. When the amp’s remote wire is off (disconnected) the amp will shut off and won’t drain power.

RCA adapters with remote wire output

Example of line level converter with remote wire output Axxess AX-ADCT2

Example of a line-level converter with a remote wire output feature. When the speaker level inputs have a signal and it creates a +12V remote on signal. When no signal is detected, the remote wire will go to zero volts and turn the amplifier off. Unlike a regular converter, these need +12V and ground connections to work.

How to connect a home stereo, smartphone, or other audio sources to an amp

What’s great is how many options you have for getting an audio signal to your amp’s inputs. In fact, nearly any analog (non-digital) jack can be used from almost any device. I’ll cover some of the main ones here:

  • Smartphones, tablets, and laptops can be used either by their headphone jack or via Bluetooth (see below)
  • Any home stereo receiver or amp can be used – even vintage ones!

How to connect a smartphone or other device to a car amp (diagram & options)

Diagram for how to connect audio signal to a car amp used in your home

Be aware that headphone jacks can be a good or bad audio source depending on your particular device. Even though they’re usually not quite as good as RCA outputs/AUX output jacks, I’ve had pretty good experiences doing using this with brand name smartphones or tablets.

In fact, I use this method to test a car amp at home.

You also use an affordably-priced Bluetooth receiver for around $25 from places like Amazon. They offer a direct line output jack or RCA jacks for this very reason.

Be sure to get a decent brand as the generic/no-name brand models tend to have sound quality problems and can produce odd noises between music tracks playing on your phone, for example.

How to connect a car amp to a home stereo (diagram & options)

How to connect a car amp to a home stereo diagram

The way you connect your car amp depends on both your home stereo and your car amp’s features. You’ll end up with one of 3 situations:

  1. Home stereo with no RCA output jacks + car amp with speaker level inputs: It’s actually fairly common for home stereos and home theater receivers to have no full-range RCA audio-out jacks. In this case, if your car amp has speaker level inputs built-in these can be connected to an unused pair of speaker terminals or alongside speaker terminals in use. The amp’s speaker level inputs will scale down the speaker signal to a much lower signal the amp needs.
  2. Home stereo with no RCA output jacks + car amp with RCA jacks only: In this case, you’ll have no choice but to use a line level converter used for car audio. Just like in #1 above, these are connected just like speakers to speaker terminals alone or alongside connected speakers.
  3. Home stereo with full range RCA output jacks + car amp: This is the easiest way by far. Unforunatley, not that many home stereos have full-range RCA output jacks. Some only have subwoofer RCA output jacks which are bass-only outputs. Full-range RCA output jacks can be connected directly to the car amp’s RCA inputs, but subwoofer RCA jacks won’t work for full-range music since they only pass bass.

What is a line level (RCA) converter and how do they work?

Image showing examples of line level RCA converters

Shown here are two good examples of speaker level converters: a 2 channel model and a 4 channel model. Both take a higher voltage speaker level signal and reduce it greatly to a low voltage suitable for the amp’s input section.

Line level converters (also called RCA speaker level adapters) are small adapters that reduce the higher-voltage signals from speaker outputs to a much lower voltage (“line level”) used by a car amp’s RCA jack inputs. They can be connected directly to a ratio, amp, or at a speaker and provide RCA jack connections.

They’re really useful because they make it possible to connect an amplifier to a signal source that you otherwise can’t.

What to do if you have ground loop noise (humming)

Example of an RCA ground loop isolator

A ground loop isolator you can use to “break” (isolate, disconnect) an amp’s RCA ground connections from that of an audio source to eliminate the electrical path that causes ground loop noise.

Sadly, noise can be a BIG headache when it comes to car amps despite them being designed to prevent it. The same is true that home stereos, too: anything that carries a signal and has a ground connection can create a “ground loop” that gets picked up by the amp and then turned into a very annoying noise you easily hear.

What causes ground loop noise?

Ground loop noise happens when there’s a slightly different potential (a slight difference in voltage) between the ground connections in an amp, stereo, and other components. Despite everything you try, sometimes it’s nearly impossible to eliminate.

In that case, you can try a simple RCA cable ground loop isolator which often solves it. Note that you shouldn’t try to get the cheapest you find because they can negatively affect sound quality.

You can find a good one for $10-$25 or above depending on the brand and features.

Related helpful articles

Don’t leave just yet! There are many more great articles here to help you learn more:

Got questions or comments?

Just reach out via my Contact page or leave a comment/question below. Thanks for reading!

How To Connect A Car Amp To A Home Stereo (With Diagrams)

How to connect a car amp to home stereo featured image

Using a car amp…at home? It’s not such a crazy idea after all! While it’s true that it’s not super easy, it’s really not all that hard and you can do it.

In this article, I’ll explain how to connect a car amp to a home stereo with clear diagrams anyone can understand. I’ll also show you all the little things you need to know before you try so you avoid disappointment & headaches.

Contents

First things first: Can a car amplifier be used at home?

Can a car amp be used at home man thinking

The good news is that YES, one way or another, you can definitely connect a car amp to a home stereo.

However, since car amps use a different power source the single biggest challenge is getting enough power to them. They also use a remote-on wire to turn the amp on & off so it doesn’t draw power and kill your battery when installed in a car.

Fortunately, these (and other) problems are fairly easy to deal with. Here’s a list of what you’ll run into when using a car amp at home:

  • Signal inputs: Not all home stereos have RCA line-level jacks, so this may require a workaround to connect to your amp’s audio inputs. Some amps make this pretty easy, however. (This isn’t much of a problem as you’ll see from my diagrams below)
  • Power source: Unlike home stereos that are powered from alternating current (AC), car amps work from a +12V direct current (DC) supply. You’ll need a +12V AC-DC power supply with enough current to run the amp. Not just any AC/DC 12V adapter will do as you’ll see later.
  • Turning the amp on/off: This is actually really easy! You can simply disconnect your DC power supply and let the amp shut off or use a simple switch to turn the amp on and off. I’ll show you how to wire the car amp so it can turn on.

The bad news is that unless you have the parts you need already, you’ll probably have to spend a little bit of money to get it working well.  The good news is that most of what you need can be found and bought new or used but you may need to order some online.

Sadly, retail stores are usually poorly stocked when it comes to power supplies that you can use for a car amp indoors. You’ll have much better luck online at places like Amazon or electronic parts suppliers.

How to use car amp with a home stereo + diagram

How to connect a car amp to a home stereo diagram

The way you’ll connect your car amp depends on both your home stereo and your car amp’s features as I mentioned earlier. You’ll end up with one of 3 situations:

  1. Home stereo with no RCA output jacks + car amp with speaker level inputs: It’s actually fairly common for home stereos and home theater receivers to have no full-range RCA jacks you can connect to the amp. In this case, if you’ve got a car amp with speaker level inputs these can be connected to either an unused pair of speaker terminals or alongside speaker terminals in use. The amp’s speaker level inputs will scale down the speaker inputs to a low signal it can use.
  2. Home stereo with no RCA output jacks + car amp with RCA jack inputs only: In this case, you’ll have no choice but to use a line level converter commonly used for car audio. Just like in #1 above, these are connected just like speakers to unused speaker terminals or alongside an existing speaker set. This will drop the signal down to a very low level that’s used by the amp’s RCA inputs. Note: I strongly recommend getting a decent quality model converter with adjustable outputs for best results.
  3. Home stereo with full range RCA output jacks + car amp: This is the easiest way by far, but not all home stereos have full-range RCA output jacks. Some only have subwoofer RCA output jacks which are bass-only outputs. Full-range RCA output jacks can be connected directly to the car amp’s RCA inputs.

How to connect the remote-on wire on a car amp

How to connect remote wire on car amp used in home diagram

In all cases, you’ll also need to wire the amp with power and a remote-on wire so it can turn on. You can do this one of several ways:

  • Jumper the remote on terminal:  When wiring the power and ground 12V connections, you can use a small jumper wire from the +12V terminal to the remote terminal so it’s on any time the amp has power.
  • Just a jumper wire + switch: Basically the same, but you can also duplicate how a car stereo’s remote on wire works by using a simple inline switch on the remote wire to turn it on/off yourself.

If you’re using a switch you can leave the AC/DC power supply plugged in if you like. When the amp’s remote wire loses its +12V signal, the amp will switch off internally and draw zero power.

Example of line level converter with remote wire output Axxess AX-ADCT2

QUICK TIP: To make things even easier, you can use a line level converter with a built-in remote wire output feature which will automatically turn the amp on or off with the speaker input signal.

Note that these do need a power and ground connection.

What is a line level/RCA converter and how do they work?

Image showing examples of line level RCA converters

Shown here are two quality examples of line level/RCA speaker level converters: a 2 channel RCA output model and a 4 channel RCA output model.

Line level converters (also called RCA speaker level adapters) are small electronic devices that connect to speaker outputs from an amp or receiver and scale down the higher-voltage signal to a low level (“line level”). The outputs are RCA jacks which can then be connected to an amplifier or subwoofer with RCA jacks.

They’re extremely handy in the car stereo world because they make it possible to connect a stereo without RCA outputs to any amplifier or powered subwoofer. We can also use them for home stereos, too.

How much do line level converters cost?

While you can get the el-cheapo ones for under $10, I don’t recommend those. Expect to spend around $15-25 or so for a good one. No need to spend too much these days as there are lots of good values out there.

What voltage & size DC power supply do I need for a car amp?

Example of how to estimate car amp current used

You can get a rough estimate of the maximum amount of electrical current you’ll need for a car amp using its maximum RMS power as shown here. However, if you’re not using an amp to its full capability you can get buy with a smaller (and less expensive) power supply.

What voltage does a car amp need?

Car amplifiers, when installed in a vehicle, work off of a voltage range as the engine runs. Although we say cars & trucks use a 12V supply, in reality, a car amp is designed to work from somewhere around 11V to 14.4V or so as the alternator in your vehicle raises or lowers it’s output while charging the battery.

Therefore you can use a power supply with a DC output similar to this, but I recommend 12V to 13.8V. Most power supplies you can buy are one of these.

What size power supply do I need?

Car amp DC power supply examples

You’ll need a power supply with a decent amperage (A) rating. Regular wall adapters won’t work as they’re very weak (0.5 to 1 amps or so). You can find 5A supplies for under $15 depending on where you shop. Desktop computer “ATX” power supplies are affordable and available in power ranges up to 500W or more. They’re easy to find but need a certain wiring connection in order to turn on.

In order to figure out how big of a DC power supply you need, you might want to calculate roughly the amount of current your amp will draw at full power. Once we know that, we can take into account wasted power that all amps use up and come up with a fairly accurate number.

Just so you know, class D car amplifiers are more efficient and therefore waste less power (and draw less current) than standard class A/B amps.

If you’re not sure what class your amp is, if it’s a class D amp it’s usually stated on the box or the amp itself. Class A/B amps often don’t state it anywhere. (Many new amps are class D so I wanted to take that into account)

Estimating amp current

You can estimate amp current based on the maximum RMS power of the amp. Don’t use “peak” or “maximum” watts as these don’t reflect the actual continuous power a car amp puts out.

As class D car amps are around 85% efficient and A/B amps are around 65% or so efficient we can use that to estimate the total current an amp would need.

Class D amp example:

Estimating the current used by a 50W RMS x 4 amp, all 4 channels used:

  1. 4 x 50W = 200W total. (200W/12V) = 16.7A.
  2. Take into account power waste: 16.7A/.85 = 19.6A
Class A/B amp example:

Estimating the current used by a 150W RMS x 2 amp, both channels used:

  1. 2 x 150W = 300W total. (300W/12V) = 25A.
  2. Take into account power waste: 25A/.65 = 38.4A

As you can see, to run a car amp at full power you’ll need a pretty big power supply! However, the good news is that it’s only if you really want to drive the amp at full capacity. For lower-power, casual listening, we can get by with a smaller (and thankfully, cheaper) power supply.

Realistic power ratings you’ll need

For just listening to music with decent volume, I recommend at least a 2.5A supply for small amps (under 50W/channel). For 4 channels or higher power ones, I’d get a 5 amp or bigger. If you’d like to have more power, consider getting 15A or above.

You can find a 5A supply for under $15-$20 if you shop carefully. 10A and 15A supplies are fairly popular so they’re usually really affordable, too. However, when it comes to much bigger supplies that will let you drive a subwoofer with heavy bass, for example, those can be expensive: $100 and above.

Connecting 2 RCA stereo outputs to a 4 channel amp

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

What if you’ve got a 4 channel amp? No problem! You’ll still use the same methods shown earlier but you’ll need to jumper either the speaker level inputs or the RCA inputs using “Y” connections to get a signal to the rear channels too.

Most car amps with front & rear speaker level inputs can be wired to 2 speaker input pairs as shown in the diagram here. When using RCA connections, you can pick up a pair of inexpensive female-to-male Y adapters to split the signal from 2 into 4 connections. (Don’t spend too much on Y adapters as you can use a decent pair of cheap ones just fine)

QUICK TIP: Some car amps have a 2/4 channel input switch built in for this purpose. In that case, setting it to the “2ch” position will supply a signal to all 4 channels. For some amps this only applies to the RCA inputs so be sure to check your owner’s manual.

Can I use 8 ohm speakers with a car amp?

4 ohm vs 8 ohm speaker power comparison graph

This graph shows what happens when you use an 8 ohm speaker in the place of a 4 ohm one. The 8 ohm speaker will work – however, it comes with a price. Since the 8 ohm speaker isn’t matched to the 4 ohm car amp, it can only receive up to 1/2 the power output and has a lower maximum volume than a 4 ohm speaker would.

Using 8 ohm home speakers in place of 4 ohm ones with your car amp won’t hurt anything. There’s a catch, however. They’ll only develop 1/2 the power of a 4 ohm speaker meaning lower maximum volume is possible.

For example, if you were to use some home stereo 8 ohm speakers instead of 4 ohm speakers, you’d notice the volume would be a bit lower than when using 4 ohm ones. That’s because a speaker needs more and more power output to increase the volume more and more; also 8 ohm speakers allow only 1/2 the same amount of electrical current to flow vs 4 ohms.

Car amplifiers & car head units don’t have a high voltage supply like home stereos and home amplifiers do. That means they’re designed to use lower impedance (lower resistance) speakers to develop the same amount of power by letting more current flow.

As long as you’re aware of this it’s ok, because they’ll still sound and play fine – you just can’t get the same power and as much volume when you crank it up vs using 4 ohm speakers.

I have a hum (ground loop noise) from the amp. What can I do?

Example of an RCA ground loop isolator

Example of a ground loop isolator you can use to break the ground conductor connection in RCA cables to eliminate ground loop noise.

Unfortunately, noise is a problem with car amps despite them being designed to prevent it. It’s also true that home stereos and amps are known to sometimes create “ground loops” between different electronic components via the RCA cables.

Ground loop noise happens when there’s a slightly different potential (electrical voltage point) between the grounds of an amp, stereo, and other components. Despite everything you try, sometimes it’s nearly impossible to eliminate.

In that case, you can use a ground loop isolator to connect inline in the RCA cables. This usually does the trick. Note that you shouldn’t try to get the cheapest you find because they can negatively affect sound quality.

You can find a good one for $10-$25 or above depending on the brand and features. The good news is that they’re super easy to use: just connect them to the RCA cables and you’re done!

More great articles you’ll love

There’s lots more great stuff to see! Here are some excellent articles that have helped many others, too:

Let me know what you think!

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