HOW AND WHY YOU SHOULD TO ADD AN AMPLIFIER TO YOUR CAR STEREO

WHY?

Why would you want to add another amplifier to an aftermarket head unit that already has a very competent four channel amp built in? The main reason is to further improve the sound quality,by giving the speakers more power to work with when it’s needed,normally referred to as “dynamic headroom”,this is power that is kept in reserve to cope with those sudden transient bursts of musical information,something that the small integrated amplifier built into all modern car head units just can’t do.

Despite all the marvellous claims by the manufacturers about power outputs in the region of 60 watts/channel from a single box unit,this just is not possible with a supply of 12 volts.All decent outboard amps have a switching power supply inside them which can take the supply voltage up to 100 volts or more as needed by the output stages of very high powered amplifiers (1000s of watts or more),something which no car radio in a DIN sized box can do as there just isn’t enough room inside it.The theoretical maximum from 12 volts is in the region 30 watts RMS/channel,but 30 watts from an amp with a switching power supply will still sound lot better than 30 watts from an integrated BTL amp as found in all car stereos.

As mentioned previously and a common misconception when matching amp power output with speaker power ratings is that the speakers should be equal to or greater than the number of watts the amp can produce,this is actually the opposite to what is true.When you hear any type of distortion coming out of a speaker,this is bad as not only can it damage the speaker(s),it can also damage your hearing.This distortion either comes from the speaker being given too much power and has reached the limits of its travel (heard as a sort of “clacking” sound as the voice coil hits the back of the magnet) which as long as you actually catch it in time isn’t all that bad for the speaker,or normally from a head unit turned up too high with not enough power is the fuzzy distorted type of sound that hurts your ears (do a Google search on “tinnitus”),this happens when the amp runs out of power or headroom for the loud passages and clips the top off the waveform,hence the term “clipping”.If this is bad enough it can burn out the delicate voice coils of tweeters in a matter of seconds,by the time you’ve figured out what’s happening it will probably already be too late.

So to summarise,more power is better than not enough,you can never have too much power,but it will eventually get to a point where any more is pointless.A big amp with the gain turned all the way down will always sound a lot more relaxed and have the needed power in reserve than a small amp with the gain turned all the way up that will always be working flat out,and not have anything in reserve when it needs it.As a general rule of thumb,even the best component speakers won’t really need any more than about 100 watts RMS.

WHAT TYPE OF AMP DO I NEED?

• 2 CHANNEL     Can be used to drive just one pair of full range or component speakers,or front and rear speakers in parallel (you won’t have front/rear fade like this),or bridged to drive a subwoofer.This option is more versatile than a monoblock if you buy an amp just to run a sub which can only do just that,whereas a bridgeable two channel can be used for either purpose.
• 4 CHANNEL      Can be used to drive two pairs of full range or component speakers,and if your source unit has front and rear RCA ouputs then you can still have front/rear fade working.Or you could have front speakers and bridged onto a sub with the amp working in three channel mode and still be able to control the sub as before using the fader.
• 5 CHANNEL      Can be used to drive a whole system that has front and rear speakers and a subwoofer amplified,all in one neat box without all the extra wiring that is needed for multiple amp installations.
• MONOBLOCK     Can only be used to run a subwoofer as they only have a single channel,but will produce better controlled and more accurate bass than a bridged two channel amp.
• HIGH CURRENT    Normally used in competition systems,but in my opinion not of any real practical use in “normal” everyday systems.They will only have a low nominal power rating,typically 50 watts into 4 ohms,but will double their power rating each time you halve the load impedance and are stable a into much lower impedances than normal class B amps,so you could expect 100 watts into 2 ohms,200 watts into 1 ohm,400 watts into ½ ohm,and if you’re lucky 800 watts into ¼ ohm.So because of this they are only really of any use when loaded down as low as possible,there’d be no point paying up to £1000 for amp that only makes 50 watts/channel would there?

HOW MUCH POWER CAN I USE,OR DO I NEED?

First of all I need to dispel a common urban myth,the cars battery has only one main purpose and that is to start the engine,along with a few other minor functions such as keeping the memory backed up on the radio,central locking,alarm etc,once the engine is running the alternator supplies EVERY LITTLE BIT OF POWER TO RUN THE CAR,the battery does absolutely nothing at this time apart from sitting there looking slightly glum and being charged.
The point to this is that adding a second battery in the boot,or putting a bigger battery in the front of the car WILL NOT GIVE ANY MORE POWER TO THE STEREO SYSTEM,in fact the rear mounted battery could make things worse as it is now another load for your already very hard working alternator to keep charged.All you can do if you don’t have enough current to keep everything properly fed is to fit a bigger alternator,generally about 170 amps is about as big as you can get,although there are some truck ones that go to over 200 amps.

The amount of power you can get out of any amplifier is limited by just how much you can put in,and in the case of 12 volt in-car equipment the power supply is the alternator with a maximum output of 120 amps in Golfs and Boras.A quick bit of maths shows that even if we could allow all of the output of the alternator to run the cars stereo system (we should normally set aside about a third to power the car) (Power = current X voltage),and as we will probably be using 50% efficient class B amps,that gives us 120 X 14 = 1680 watts of input,or 840 watts output once all the rest of it has been turned into heat.

It really doesn’t matter if we do have a nice personally signed certificate with our amp that says it has been tested at 3,150 watts,this figure will only be nothing less than a dream without the worlds best power supply,and in our cars sadly we don’t have this.

WHAT DOES ALL THE JARGON MEAN?

• CLASS A     This specifies how the power supply and output stage of the amp works,it is the least efficient of all the designs and as such is really only suitable for small power outputs,but is generally regarded as being the most accurate or “musical” of all.
• CLASS B     This is the most commonly used of all the amplifier types because it is a lot more efficient than class A,meaning that much higher power outputs can be easily achieved.This design produces more distortion than class A does,and is less linear in its operation,meaning that the output doesn’t always faithfully follow exactly what the input does.
• CLASS D    The most efficient of all the designs that uses a digitally switched power supply that gives an amp that is a lot smaller than its equivalent class B and also generates a lot less heat,but was always considered to be not as musical giving bass that lacks any real bite or “oomph”.The newest generation of class Ds are considered to be the next evolution of in-car amplifiers that may soon replace all the other more traditional types,examples of these are the Alpine PDX,Pioneer PRS and the JL Audio HD range due to be with us this summer (2008) that promise to push class Ds up the next level.
• EFFICIENCY    This is a measure of how good the amplifier is at converting it’s input power into output power,class A are only about 35% efficient (we need about 1400 watts of input to produce 500 watts of output),class B are about 50% efficient (1000 watts in for 500 watts out),and class D are reckoned to give up to 90% efficiency,so that 500 watts will now only need about 550 watts of input,so less strain on your cars charging system.
• CROSSOVER      Most good amps will now have some sort of crossover built in,if it has two or more channels it should have either a Low Pass Filter (LPF) which cuts off the midrange and above to send just bass to sub which ideally should be variable between about 50Hz and 150Hz,and a High Pass Filter (HPF) that cuts off the bass to the full range channels,ideally variable from about 50Hz up to maybe 200Hz.Not always needed now as more lower priced head units now also come with crossovers built in.
• PROTECTION CIRCUIT     This refers to the built in device that switches the amp off if it detects a short circuit or a short to earth on the speaker wires,or if the amp should overheat,indicated either by the power on light changing colour or another one lighting up instead.
• OUTPUT POWER        RMS (Root Mean Square) and peak are the only two true power ratings that actually mean anything.
  Peak = RMS X 1.414,so 100 watts RMS also exists at the same time as 141 watts peak
  RMS = Peak X 0.707,so 100 watts peak also exists at the same time as 71 watts RMS
• IMPEDANCE     The range of loads that can be safely connected to the amp,normally they are optimized for use at 4 ohms,and will in theory double their power every time you halve the load impedance,although most will only work down to 2 ohms. 
• FREQUENCY RESPONSE       Normally from about 10Hz up to 30KHz or more,slight differences are of academic interest and won’t be audible.
• DISTORTION         Anything less than 1% isn’t audible,so there is no point choosing an amp with 0.000001% over one that has “only” 0.00001 %,in fact some sorts of distortion are good,but these simple figures can’t really tell us anything useful.
• S/N RATIO         The signal to noise ratio needs to be as big as possible to ensure that the background hiss generated by all electronic circuits is as far below the level of the signal as possible,any good amp should be at least 70dB or more,the best will be over 100dB.
• GAIN CONTROL      This is actually a misnomer as it doesn’t alter the gain of the amp,it should always be called and used as an input sensitivity control (or level),and NOT as a volume control.Typically it should go down to about 0.5 volts and as high as possible to match up with the ever increasing trend for high output head units,5 volts or more being not uncommon nowadays.

HOW DO I INSTALL IT?

• POSITIVE POWER CABLE   The part of the system that you need to get right more than anything else,and the one that I see causing more problems than any other after RCA leads. 
  The connection is normally made directly to the positive terminal (except for VERY high powered systems where it would go directly to an uprated alternator),the photo below shows how I normally connect it in these cars by drilling a hole through the busbar from the positive terminal to the fusebox,and then putting a 6mm nut and bolt through to hold it SECURELY in place (the tightness of all these connections cannot be stressed enough).

If you have the later type of fusebox with a length of red insulated cable instead of the busbar connecting it to the +ve battery terminal,then you can bolt it straight on to the terminal.
You can screw the fuseholder to the metal strap that clamps the battery down as I’ve done,but make sure you use very short screws,and undoing the clamp and lifting it clear of the battery would be a very good idea.
You can run the power cable through the black plastic trunking as shown below that runs towards the back of the car (the lid unclips,you will need to remove the airbox and MAF on most cars),and then out of the hole in the back of it.

You will need to pull the soundproofing back to see the main grommet on the nearside of the firewall,it will have a number of spare nipples that will need to have the end cut off one of them (they are tough,so this will need some effort).

It may be easier with two people to get the cable into the car,one on the outside to keep pushing it through,the other one will need to put his/her head in a position to be able to see into the gap between the heater and the inside of the firewall,a lot easier if you have no air con or climate control as the gap is wider,more difficult if like me you have manual air con as the gap is smaller.A pair of very long nosed pliers will be the best way to fish it out once it becomes visible,it may need lots of pushing it in and pulling it out again until eventually it will go in the direction you want it to.

Once inside the car you will need to unclip the inner sill plastic trim (easy to do without breaking anything as the clips are metal),then the kick panel plastic trim also with the same clips,the B pillar trim if you have a five door also unclips,and if you have a three door then you only have to lift the back seat,the seatbelt could also do with being unbolted if you really want to do the job properly.

The photo below shows the channel pressed into the inner sill that the power cable can be run along,leaving no embarrassing bulges.

• FUSEHOLDER ………Mounted as shown above,or if not as close to the battery as possible,sound off rules normally ask for 18 inches or less.
  I would recommend never to use the AGU type of fuseholder that has the cylindrical glass fuses for two reasons,the first one being that almost all the fuses are made very cheaply in the far east and have a habit of the solder connection breaking between the inside of the end cap and the fuse link itself,leading to a high resistance,which can generate enough heat to melt the fuseholder.They also never make a very good connection between the fuse and the holder simply because of very poor tolerances when they are made,again the result being that they get very hot,the contacts lose their springiness and fail to grip the fuse anymore.
  The ANL type of fuseholder is much better,the ANL fuse as shown below is made of one continuous piece of metal,and is bolted firmly into its holder,so there is no chance of there ever being a bad contact.
  These fuses are available with current ratings from 80 amps up to 300 amps,but normally in cars with stock charging systems it’s unlikely you’d ever need one bigger than 80 or 100 amps.

• CRIMP CONNECTORS ……If you don’t have the proper tool to crimp the big terminals (such as 4 SWG size) then don’t try to do it in a vice or with Mole grips,if you do try it this way,afterwards grip the terminal firmly in a vice and pull the wire as hard as you can,if there is ANY movement at all then it would be better to solder them.
  If you do solder them make sure you get lots of localised heat around just the terminal,and get it as hot as possible without melting too much insulation,you must be able to see the solder flowing in and around the strands of the wire,if you don’t get it hot enough you’ll only get the clear flux around the wire which can cause a high resistance connection which is not good.
  If you don’t have enough heat to solder or enough pressure to crimp,then a compression style connector as shown below would be better,but again make sure it is REALLY tight.just doing it by hand won’t be good enough,a vice and a spanner or similar would be better.

• POWER DISTRIBUTION BLOCKS(PDB)……If you have more than one amp then the proper way to get power to all of them would be with a power distribution block,it will have one or more large sized inputs and normally four or more smaller outputs,it is ok to use smaller gauge wire for the short runs to the amps as the voltage drop will be a lot less than the long run from the front to the back of the car,if your main power cable is 4 SWG,then 8 SWG from the PDB to the amps is fine.
  I don’t think it’s necessary to use fused PDBs as all amps now have their own fuses in them,and the extra voltage drop across them can only make things worse.

• EARTH CABLE…….With multiple amp earths you could either use PDBs as above with one thick cable in and thinner ones out (4 and 8 SWG again),or earth the amps individually but all in the same place.One of the seatbelt mounting bolts would be good as it will make contact through the thread of the bolt and captive nut,or even better would be to drill a hole through a solid part of the chassis,sand or grind the paint away to reveal bare metal,and finally put a bolt and locknut through and do them up as tight as possible.
  It always amazes me how many installers use the fattest power cable they can,and neglect the ground cable in favour of any old bit of speaker cable they have lying around,and then clamp it under a plastic nut that holds the rear light cluster in place.

DON’T FORGET THE EARTH CABLE IS A RETURN FOR ALL THE POWER THAT FEEDS THE AMPS,THEREFORE THEY CARRY JUST AS MUCH CURRENT.

• RCA CABLES……..Need to be kept as far away as possible from the main power cable (they can cross but musn’t run parallel).No amount of screening will stop them picking up interference if they’re too close to ANY source of electrical noise,£50 triple screened will be just as useless as £10 ones with moulded on plastic plugs,the only thing that will stop the noise is distance from the source.
  To achieve this they need to be run down along the right hand side of the car,starting obviously at the back of the head unit.The panels above the drivers knees and feet can be removed by undoing the Torx T20 screws to get the cables across to the kick panel,which will need the bonnet pull removing to get behind it.
  Insert a flat bladed screwdriver in where shown,and lever towards the back of the car,the retaining clip should fall out and drop down behind the panel.

The rest of it will be the same as for the power cable along the other side of the car,I always run one more cable than I actually need so I don’t have to strip the car down again should one of them go faulty.

• REMOTE SWITCHING WIRE……..Connected to the blue or blue/white wire in the loom at the back of your head unit,but make sure you read the instructions as with some the wire will only be powered when the radio is on (the aerial wire) and one on all sources.This will be connected to the “REM” or “SW” terminal on the amp(s) and can be thin wire as they only need a very small amount of current to switch them on,and will normally be run with the RCA cables,but can just as easily go with the power cable.

ALL THE WIRING IS IN THE BOOT,WHAT NEXT?

• CONNECTING THE WIRING TO THE AMP……Whenever you connect electrical items that can draw any appreciable power you should always connect the ground or earth cable first,the power,remote and RCAs somewhere in between,and the very last job to do is to put the fuse in.
  Don’t forget that any half decent amp will have capacitors in that will start charging as soon as you give the amp 12 volts,so expect a spark as the fuse goes in.
• PRE FINAL INSTALLATION CHECKS……..It is always a good idea to test the amp at this stage before you screw it down just in case………….
• WHERE CAN I MOUNT IT?.......Because heat rises ideally it should face upwards with an unobstructed airflow around it (especially large bass amps that can get too hot too touch).If not and they have to be mounted on the back of the seat,if possible the fins on the heatsink should run vertically to help the heat to escape.Under no circumstances should amps ever be mounted upside down as the heat will be trapped inside the heatsink and it will overheat and hopefully switch itself off,if you do have to mount them this way or in an enclosed space such as an amp rack,then you must have fans to draw air across them,but don’t forget one has to blow and one has to suck,not both of them doing the same thing.
• FIXING IT DOWN……….Don’t use the amp as a template unless you want drill chuck marks on your heatsink,instead stick a couple of strips of carpet (gaffer/duck/duct) tape under where the screw holes will be,mark through onto the tape with any handy pointed tool,move the amp and drill the holes,and finally screw it down.
• SET THE GAINS……..Didn’t I say not to call them gains? Anyway turn the amp level controls down to minimum (anti-clockwise),turn your head unit up to about ¾ of it’s maximum volume,and then slowly increase the level on the amp (s) until the sound is as loud as it will go without distortion.
  This is a good compromise as it gives you a bit of extra headroom for any quiet tracks,too high and you’re more likely to hear unwanted noise.

That’s about it for choosing and installing amps,if you need to know anything more on this subject don’t as me as I copy and pasted it all from Wikipedia.

Chris.

This guide is fantastic and has dramatically improved my understanding with my install.

Adjusting the gain has made a great difference in getting read of the distortion.

Ill be honest i just put it straight to max when i first put it in

And an added bonus is i actually feel better knowing that its all done properly.

Thanks,

Craig

 Invaluable advice, thanks alot mate!

mods, this should be a sticky?

Agree- Sticky please!

I will be using this guide this weekend - fingers crossed !

Great post imagewerx.

Like the quote "you can never have too much power". Reminded me of reading about someone blowing out their rear window.

You know too much my friend, hat off to you. Now i know i will definatley not be able to tackle this one myself.

shammy:

You know too much my friend, hat off to you. Now i know i will definatley not be able to tackle this one myself.

Aaaawwww go on,give it a go it's almost all plug-and-play,lots of people who've never done it before have done it and learnt more about their car in the process.

Chris.

 I'd absolutley love to give it a go but i honestly jsut think I'll mess up more than I'll achieve. Just bought a two channel amp and some components aswell

Is it worth adding in a sizing guide for the power cable?

It's pulling out all the trim/seats to run cables that I'm scared of lol. Hamfisted get like me I'm bound to crack & break some of it lol.

What a brilliant write-up though

Roger Irrelevant:

It's pulling out all the trim/seats to run cables that I'm scared of lol. Hamfisted get like me I'm bound to crack & break some of it lol.

What a brilliant write-up though

 

Ta everso,but apart from Volvo's,this era of VAG cars are some of the easiest to take apart and put back together of any cars ever made.

A good tip when taking any plastic trim off in this weather (it's cold in case you didn't know) is to gently warm it up with a hair dryer or heat gun firts on it's lowest setting,very cold plastic can get to be VERY brittle even on relatively new cars.and if you don't take cars apart every day you don't have the feel for just how hard you can pull a piece of plastic before it becomes two pieces of plastic.

The sill trims and anything you need to remove to run cables is so flexible it can almost be bent double when it's not cold,trust me the job is a lot easier than most people think.

Chris.

 Chris, How do you take the front seat out or is that not neccesary?

Thanks

Dont need to take front seat out. THe runners along the doors just pop up with 2 screws behind the B pillar trim.

 Thanks buddy

Ill take a few pics of when I come to put my components in for removing the trim.

I only took the seat out to take the photo,but isn't it also nice to vacuum clean all those little nooks and crannies that hide chips,M&M's and domino's?

Chris.

Does anyone have pics of their systems where they have used a vibe active wiring kit? Im really looking for what it looks like around the battery really with their fuse! Also any reccomendations on where to put the remote if you have one that controls the volume and crossover? I was almost thinking of putting it up in one of the unused sections by where the hazard lights button is, or possibly in the armrest for a more stealth operation? What have other people doen? After this thread, Im almost ready to do it, but going to wait till I have an extra pair of hands to help me. Cheers

 I put my remote under the arm rest so i could easily reach it without opening it while driving

Aaaaahh! Thats a good idea, hadnt thought of that, very out of the way, and I might not have the remote when I do the main install, so wouldnt really want to tear everything up all over again, and that could go straight down the middle into the back! Nice One!

 i ran my cable down by the passenger seat out of sight and up the door pillar where the passenger seat belt is, and ran it under the door trims into the boot, and btw it doesnt catch on the handbrake, or anything for that matter, the leather was worn before hand!

Seb

Right, Im having trouble getting the bonnet pull off so that I can get the wire behind the kick panel. I did what it says on the guide at the top of this page, but it wouldnt work, I assume it is the little black plastic part behind the bonnet pull that is attached to a wire. I spent about 20 mins trying to do it, and then took a break for the rest of the day, and am going to try and tackle it again tomorrow!

One other question. Is it necessary to take the head unit out to put the remote, and RCA cables in? Or can you get to it by taking the second layer of black plastic that is along the side of it? What is the best way to do this?

Any help is greatly appreciated, and I did get the left side of the car (power cable, fuse, and ground) done today, now I just need to get the right hand side of the car done!

Thank you!

Getting the bonnet pull off really is as simple as I've already explained,the cable is attached to the hub that is left behind when you take the lever off,not really anything more I can say to explain it any better.

Take the headunit and the cubby hole out,push it back in while guiding the wires in with your other hand,put the cubby hole back in.

Chris.

 Chris i gave it a go, and it's not going to badly i just can't seem to get the power through, I've taken the glove compartment out and the other bits of trim, but ir's just not happening, any tips?

Thanks

trogolodyte:

Right, Im having trouble getting the bonnet pull off so that I can get the wire behind the kick panel. I did what it says on the guide at the top of this page, but it wouldnt work, I assume it is the little black plastic part behind the bonnet pull that is attached to a wire. I spent about 20 mins trying to do it, and then took a break for the rest of the day, and am going to try and tackle it again tomorrow!

I had the same problem as you when I did mine, despite also reading guides and posts on it. The little part you describe above with the cable directly attached should not come off - if you manage to lever that off then you've broken it!
What you're doing wrong is trying to lever *behind* the bonnet pull - ie you've been looking for something behind the whole bonnet pull, which roughly lined up with the arrow in Chris' photo; that is what I spent ages trying to do too. This will never work because the clip actually slots *inside* the bonnet pull, in line with Chris' arrow, behind the front face of the bonnet pull. It's a plastic circlip at one end and it levers out with very little effort, so if you're using a lot of force then you've not found the right place. You'll need to have the bonnet pull in the 'open' position in order to have enough space to pull the clip all the way out.

Once I finally sussed it out I felt rather sheepish at how easy it was vs how long I'd been struggling, I was like "Ahh, so *that's* what he meant, doh!". I took some photos whilst I had the handle off, in case anyone else would struggle due to having the same thought process as me! They were only quick camera-phone efforts so I'm not sure how well they came out, I'll go hunt them down and update this post...

[edit]... here you go. Sorry about the shocking lack of focus on the first two, hopefully all should be clear though once you see these, even if the photos aren't:

Hope that helps

Bump, Someone must have some tips about getting the power cable through?

Thanks for any help

Use the large grommit behind the plastic ducting to the right of the engine bay.  Comes out behind the glovebox.

 Yeah, I've used that. Completley removed the glovebox and other parts of plastic trim, is there something i missing?, i just can't see where it comes through on the inside of the car. Thanks

 Great Guide Chris!

One point, what about the installation of a Speaker to Phono convertor? Could help those with stock HU's.

Joe

shammy:

 Yeah, I've used that. Completley removed the glovebox and other parts of plastic trim, is there something i missing?, i just can't see where it comes through on the inside of the car. Thanks

 

The grommet is hidden behind sound deadening if your looking from the inside out. Look for a large loom that is around 3cm in diameter that comes out of the material. This is where the grommet is located. To get through it get a wire coat hanger or small screwdriver and poke around CAREFULLY near the loom to create a hole.

Joe

shammy:

 Chris i gave it a go, and it's not going to badly i just can't seem to get the power through, I've taken the glove compartment out and the other bits of trim, but ir's just not happening, any tips?

Thanks

To get it through, get a coat hanger or similar through, tape the power cable to the coat hangar using duct tape and then use some sort of silicone spray such as windows cleaner or WD40 to give some lubrication of the power cable on the rubber grommet, and carefully pull it thorugh. Tape it tightly so the spray does not get under the tapes surface causing it to slip. Persist, you will get there in the end.

Joe

Joe90k:

 Great Guide Chris!

One point, what about the installation of a Speaker to Phono convertor? Could help those with stock HU's.

Joe

HOW VERY DARE YOU!!!! The children of satan in one of my how to's? Actually probably only distant cousins,but why would you need them if all stock head units have pre-amp level outputs?

Chris.

Are we talking only golfs? or all cars? Confused....

Joe

Well how about saying about the use of a PC3-11 then instead?

Why do you hate speaker to phono's so much then? Whats wrong with them...

Joe

Joe90k:

Well how about saying about the use of a PC3-11 then instead?

Why do you hate speaker to phono's so much then? Whats wrong with them...

Joe

This was intended more as a guide for installing amps in mk.4 Golfs and Boras specifically,where such a thing would never be needed,and I don't hate them,I was LOLing without the LOL.

Chris.