How to Properly Hook Up a Car Amplifier Inside the House




Introduction: How to Properly Hook Up a Car Amplifier Inside the House

About: My name is Alen and i study electronics engineering. I love to make anything that needs electricity, hack and mod things or building anything AWESOME...

Hello everybody, recently i bought car amplifier for repair and decided that im gonna replace my Sony XM-4020 that i have been running as my subwoofer amplifier for a year now. I took this opportunity to write instructable on how to properly hook car amplifier for use inside of your house (connected to mains voltage) and what you should be careful about.

There are many reasons why you would want to use car amplifier, but if you can choose between proper 120v-240v amplifier and car amplifier i would suggest you to pick house amp, its power supply is well designed and you will get proper power output out of it. Car amplifiers are mostly rated at 14,4V and lower impedances (1 or 2 ohm for example) while some home amplifiers can only go as low as 4 ohms. Since you will be running it off 12V power supply (more about that in further steps) you might not get as stable power as you would in your car.

If you however still choose car amplifier then continue reading as i will try to provide as many information about it as i can.

I've been running car amplifiers in my room for 6 years or so, it used to be hard to get proper amplifier and if u were like me you probably had spare ATX power suplies so you could save a few bucks on that. These days it's much cheaper and easier to just get 24V chip amp from ebay and have decent setup. Even designing and building your own, internet is full of schematics that are just waiting to be built.

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Step 1: Choose Your Warrior

If you already have amplifier you can just skip this step.
If you still haven't got one and you are thinking about buying it there are few things to consider.
Mainly when choosing amplifier you are gonna choose between Class AB and Class D designs. Most people are using class AB on mids and highs (midrange speakers and tweeters) while going for class D on subwoofers. Reasons for this are that class AB has better sound characteristics. There is a lot of discussion about this so i'm not gonna go there, but main difference between them is power consumption. While class D has excellent efficiency of +80%, class AB might be only about 50-60% which means they will also heat up alot more. This is thing to consider when choosing PSU and desired output power. If you have smaller amplifier (less than 250W) it may not be problem since even with 50% efficiency it would only draw 500W, however if you have bigger amplifier it would draw insane amounts of power so you will need bigger and more expensive power supply.

On last 2 pictures you can see difference between GZTA 4.120mk2 (class AB) and GZTA 1.2000mk2 (class D). Both amps were set to 20V output (about 100W to 4ohm dummy load), class AB is drawing 17.6A (230W at 13V) and class D is drawing 11.8A (150W at 13V). This means that by using same power supply (next step) you can get more power with class D amp.

Step 2: Choose Your PSU

Since you have your amplifier, you need 12V power supply to power it up.
PC ATX and Server power supplies offer a lot of power and they can be cheaper than other solutions. Only downside is they provide only 12V and not 14,4V. This means you are gonna get a bit less power than your amplifier is rated at (some are rated at 12V and at 14,4V, some only at 14.4V). Other alternative is to get 12V power supply for LEDs or other things. These have small potentiometer so you can adjust voltage a bit higher, usually from 11-14V.

PC ATX usually requires green wire to be connected to negative terminal to power on. You can use simple switch to short them together. You will also need to cut off connectors and bundle together all 12V wires and Ground.

Modifying ATX power supply for 14V output can be done if you have some electronic knowledge, but if you dont then you shouldn't be opening one. They contain capacitors that are charged up to mains voltage and can be deadly. For this reason i'm not gonna go further, if you are good with it you wont have any problems with it since its as easy as changing few resistors.

Modified ATX (PC PSU) for car amplifier - 14V output

Testing My Modified ATX PSU

How much power?

Now we come to a part where difference between AB and D class comes in play.

Add together power of all channels, for example if your amplifier is 2x250W you get 500W, if you have monoblock 1x500W or just bridge 2 channels use power that its rated at. Good rule of thumb is to multiply that by 1.5 for class AB and 1.2 for class D. So your 500W amplifier actually draws 750W if its class AB or 600W if its class D. Add about 50W of headroom to that. Divide that by 12V and you roughly need current of 67A for class AB or 55A for class D. Check if your rating is a bit higher than your fuses on your amplifier. If you go under it, it may not be enough to blow fuses which could lead to damage of your wires, power supply or even burn them down. Now you see why its better to get class D for higher amounts of power, that's 200W difference for 500W amplifier.

Step 3: Wiring

Use max current rating of your power supply to choose your wire gauge. Its always better to get as big wire as you can connect to your power input that is as short as possible and then use longer wires to your speaker. With higher power amplifiers its good to also include fuse that is recommended with your power wire.

Use online charts to roughly calculate your wire gauge, but its always better to get bigger gauge as they will have less drop in voltage with higher current draws.

I included diagrams for connecting psu to amplifier but if you have any questions just ask me in comments since your setup might be a bit different.

You can use switch between REM and Positive input to turn on inputs, however best would be to use DPDT switch and use one side to short REM to Positive and other one to short Negative to Green (PS_ON) wire on your ATX PSU. This way your PSU would turn on at the same time as your amplifier. Alternatively you can use simple SPDT switch to short Negative to Green (PS_ON) and just put jumper on REM and Positive input.

Ground is not same as Earth on your PSU so don't connect Ground to PSU case! Case of your amplifier is negative or ground terminal but PSU is earth, shorting them out will cause ELCB or other breakers to break.

For audio input you need RCAs. Simple 3.5mm to RCA will do the trick if you want to connect it to your pc or laptop. If you already have receiver or other device that has RCA output then you need male to male RCA cable. You can get them in any bigger shop or even online.

If you have bass knob it simply goes inline with your RCAs.

Step 4: Batteries?

If you have high power amplifier and simple PSU wont get you enough power you could consider getting 12V batteries. Don't get open types since they can produce a lot of hydrogen while charging which is not good considering you are going to have them in your room.
SLA or Gel types are good for this since they are mostly closed and have better discharge capabilities (deep discharge). This would require a bit different approach since you will need to get 14V-15V (0.5V drop from diode) from your power supply and add diode in series. Diode should be high power, rated at least few amps more than your max charge current, high power bridge rectifier could also work since higher current ones can be screwed to heatsink. You will need to put switch on mains input of your PSU if it doesn't have one since overcharging lead acid batteries is never a good idea.

As safety precaution you will need to add fuses since they can provide much higher currents (up to 200A for single 10Ah battery!) for shorter periods which means it can definitely burn even higher gauge wires.

Unless you are doing something crazy just skip this step, in my opinion it isn't worth it for daily listening at normal levels.

Step 5: Setting Your Gain, Matching Power

If you wired everything correctly, you can turn on your amplifier now.
See, that was easy. Now comes the tricky part, since all setups are not equal, you might get less or more power than advertised. Setting gains isn't that hard if you have SMD DD-1 or oscilloscope. Turn every filter, bass boost and gain down and turn bass knob or volume knob all the way up and leave your audio source at about 50%. Get 40Hz test tone for subwoofer amplifier, or 1kHz for full-range amplifier. Its safest to tune it at 0dB since that way you can't clip output signal even if you listen to rebassed or bass boosted music. If you dont listen to those types you can get -3dB or -6dB but you might clip it with some music. Hook your audio source to amplifier, play test tone and turn the volume up. Your audio source might clip so firstly checking outputs with DD-1 or oscilloscope should reveal any distortion or clipping, if everything is ok you can raise your gain until waveform starts looking distorted (as on pic 2) or clipping LED lights up on DD-1. This should be done while your speakers are hooked up and using few test tones. Since your speaker has impedance which varies by frequency you are playing it at, its always best to play different tones to see if amplifier distorts.

I don't have SMD DD-1 or oscilloscope, what should i do?
Well you can do this by ear but it wont be as accurate. Simply do everything as described before, but when you raise volume up listen to change in sound. It's hard to describe it but you will notice that your speaker will change sound when it starts to distort. Again make sure you do this at multiple frequencies to ensure output is completely clean.

EXO made a good tutorial about that, so if i'm not clear enough watch this video or ask me in comments.

How To Set Amplifier Gains & Get MAXIMUM Output w/ NO Clipping

Step 6: Problems?

My amplifier makes much more power than my speakers can handle, will that be problem?

Some speakers can handle more power than rated without getting damaged, some may not. To ensure you are not getting more power to them, use nominal impedance rating and ohms law to determine how high should voltage on output be. For example if you have 4 ohm speaker that can handle only 100W, play test tone and raise gain until you get 20V on outputs and make sure waveform isn't distorted since clipping hurts speakers more than getting too much power to them.

My power supply shuts off when raising gain, what could be the problem?

Getting power supply from china or suspicious sellers might not mean you will get exactly what you wanted, your power supply might not output as much current as it states on it. Try measuring voltage on outputs of your PSU, if it drops too much it may trigger undervoltage protection to prevent any damage.

My amplifier gets into protection when raising gain, what could be the problem?

First make sure your amplifier is stable at impedance of your speakers. Dont run 1 or 2 ohm speakers on amplifier that doesn't say its stable at those impedances. Check voltage on power inputs of your amplifier, if it drops under 10-11V it may trigger undervoltage protection on your amplifier. Some amplifiers have multiple colors of LEDs to indicate so check your manual.

I'm gonna expand this list so comment if you have problems.

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    11 Discussions

    The Great Western Alder
    The Great Western Alder

    Question 4 weeks ago on Step 5

    I have 2 DD Audio DMF1600 amps powering 4 Klipsch speakers. I wired my speakers to get 4ohm load on the amps which gets me 800w per amp

    My PSU is

    The issue I'm getting, is some square wave coming through somewhere. A very noticeable hum that increases with volume. I bought a ground loop isolator for my RCA connections and it helped some, but I still get a loud 40hz range hum that'll shake my room when I go 3db above reference level. I'm using a Denon avr-x4500h reciever, and only have RCAs from the AVRs pre outs hooked up to the 2amps. My entire purpose to the big power is to get as far above reference level as I can with clear sound.

    Should I try wiring my power supply through a deep cycle RV battery I have kicking around? I can tune my stereo and consider myself knowledgeable, I helped my friend get his Bryston setup going, but this car/home audio Frankenstereo I'm building is a new territory for me lol. Any advice would be much appreciated


    Answer 27 days ago

    Are you sure it's square wave? It sounds like it could be ground loop issue. I tried many things to do but with some amps it's just really hard to get rid of it. One thing that helped me the most was isolating ground (earth) connection on psu.
    You could try different psu (or battery in this case) to see if that removes the hum, but make sure that your battery can output enough current. It could be your PSU that is causing interference and this you will know with this test. Can you hear hum without anything connected to the audio inputs? Does your receiver output clean audio signal?

    The Great Western Alder
    The Great Western Alder

    Reply 21 days ago

    I do appreciate the reply! I've isolated the problem. I get a slight buzzing from my AVR outputs, but the RCA ground loop isolator solved that. I wired everything through my deep cycle battery, but only ended up using that as a ground. I'm both impressed and disappointed with the setup. It's as loud as I want but in hindsight I wish I checked my amplifiers THD lol. It gets super loud but cloudy, that's just the THD sadly. One day I'll get Brystons 😎. I left you a link of my frankenstereo btw. Peace my friend 👍


    10 months ago

    If you want to make a true well made power source for testing car audio amps and preamps at home. Or for using car audio in your home, then I would suggest using a 100 watt solar panel mounted on your roof or outside a window in the sun close by where you will be listening. And a solar battery charge controller hooked up to a 100 amp hour deep cycle battery. You can find the solar panel & charger controller for around $125 on eBay. And also the deep cycle battery 100ah for around $200.

    Together you will have all the power you need to build a home triamped or biamped car audio system. The only downside is toward evening the battery will no longer be charged by the sun and will no longer have unlimited reserve power, like during daylight since it is not receiving solar charge during darkness.
    So you will have to setup a 110v battery charger for the night and early morning hours to keep battery topped off. So doesn't drain more than half it's capacity.

    Solar charging is inaudible while you listen to music, but using a 110v battery charger, you will hear transformer hum in the audio. So best to use your car audio system for music during daylight and not more than 2 hours after sundown.


    Reply 9 months ago

    For testing 12V battery and 5A psu should be more than enough (which is what i use), for listening however you would need way more than 100W panel, class AB amps can draw 20-30W just by sitting idle, my 2kW ground zero amplifier draws 20W at idle and it's class D. If you have 2 amps (one for sub, one for mids-higs) that would draw as much as panel would put out during cloudy day.
    100Ah battery would help with high current draw but SMPS PSU is best option, or high current 12V charger like CTEK makes but those are really expensive.


    Question 10 months ago

    hi, i a'm thinking about car sub and car class d amp in home, can't i just use a car battery, and constant trickle charge, i can see, this seems complicated, or just a higher amp a/cxd/c converter like 50-60 amps at a 300 watt car amp, to power my sub, signal directly from sub out on receiver


    Answer 10 months ago

    50-60A psu should work fine with 300W class D amp. As a good rule of thumb you should get psu that can produce same or higher current than fuses can take (usually 30-40A on 300W amp).
    Car batteries are usually made just to start car and not really for discharging them completely so if you would go that route you should use deep cycle battery. Constant trickle charge is not good, with open batteries it will produce a lot of hydrogen and that won't be good if you use it indoors, SLA on the other hand might lose some of acid (due to evaporation) and since they are closed you can't add it (you can but it's a bit more complicated).


    10 months ago

    Would a 6x9" speakers with an 8" sub through the amp and two pc power supplies work? As I ideally don't want to use a battery for the extra power.


    Reply 10 months ago

    Depending on power of amplifier and power supplies.
    You can always turn down gain on amplifier.


    Question 11 months ago

    In step 4, are you saying you are able to connect the PSU 12v wire directly to the car battery? Then from there, go to the car amp? Isn't there concerns about overcharge or heat?


    Answer 11 months ago

    You should use diode like shown on schematics and explained in step 4 since you can burn some PSUs by feeding 12V to their output.
    There is a chance of overcharging your batteries if you have PSU that can deliver more than 14V so it's good idea to use switch to turn off psu, in case you are listening at higher levels you are gonna ask for a lot of current from battery so there is very small chance of actually overcharging battery. Alternative is to set PSU to 13-13.5V since this is safe voltage to let your battery sit at or even get charge controller.