Two questions:
1) What are the benefits + disadvantages of a single 5 line amp vs a 4 line and a seperate amp for the sub?
2) How many pre-out lines is best for going into amps? The more the better? Or is one 4V pre-out line enough to sound good?

(The reason I ask the second question is that I have a iPod and the Alpines look good for that, but I don't know if I can get away with the $230 hu or if it's really worth the $330 one for more pre our lines...)

 

I have a 5 channel amp, if I had to do it over, I'd get a 2 channel for the front doors, mono sub for the rear and not have anything in the rear doors. Since I have the 5 channel, I might put some decent speakers in the rear (possibly for some midbass) or I'll just bridge the outputs to the 2 fronts, haven't decided yet but am leaning towards bridging it. I'm going to get a deck with 3 sets of pre-amp outputs since I'm running everything through the amp anyhow. I'd like to get an I-pod as well, have been looking at the Alpine decks too. As far as pre-amp output voltage, I think (I'm not an expert) you need to check to see what your amp can take.

 

ummm... you can or should be able to bridge 4 of the 5 channels.

so you end up with a 3 channel amp. the 4 channels bridge into 2 channels, but twice the power.

say you have this:

4x100 + 1x200 watt amp.

you take the 4x100 part and make it into a 2x200. use that to power a kick *** pair of speakers for the fronts and it will rock.

 

That's the question I need to decide the answer to (whether I want to do it or not).

Edited for clarification

 

1 five channel amp usually has less power than two amps but it is also more expensive. I would get two amps if I had the money and I'd also get at least a 1 farad capacitor.
A stereo with a 4volt preout should also have more features than the stereo without it. The 4volt preout will make the system sound better and help eliminate any engine whine as well.
It basically all comes down to the money and how much you're willing to spend.

 

1. usually costs and space saving.

costs since there is one chassis and sometimes just one power supply to power the entire amp.

and since 2 amps are sharing just about everything, it might come in a shape were it is smaller if 2 of the same amps (from the same company) are used.


2. number of pre-amp outputs mean you can fade from front to rear and balance from left to right. otherwise, you are still ending up with a 2 channel (stereo) system.

but if you just have one amp, those other pre-amp outputs wont be used.

now, the reason 4 volt outputs are a good thing is that in general, you want to crank the volume or output setting of the device that has the highest SIGnAL TO NOISE (S/N) RATIO numbers as high as possible. while keeping the device the with the lowest S/N number as low/soft as possible.

take for example, a good head unit that has a S/n ratio of 110 dB S/N. and then take a semi good one that has a S/N of around 80 dB.

if you take the 2 heads and connect them one at a time to a system, and set their volume (or gain) to 70% of their max output (measured and confirmed), the one with 80 dB will have more noise on the system.

now if take the opposite and have 2 diff amps. one has 100 dB (a good one) vs one that is around 60, you will hear that the good one will have less noise than the second one.

what does this have to do with 4 volt outputs?

well a few years ago, the normal output was around 2 volts. so with 4 volts, you can essentially double the output amount while still keeping the same amount of S/N noise going through the system.

normally, when i setup my systems, i crank the hed unit volume to around 3/4s up and i turn down the gains on the amps. then i play something i would normally listen too. i start to turn the gains on the amps, meanwhile, listening for distortion to come on. usually, this is when the part of the song is the loudest.

if you take the 2 head unit test, you'll notice the the gain on the amp is about half of that from the 4 volt to the 2 volt one.

now remember this is in theory. in the real world, it may not be an actual 50% increase, but there is a diff.

and since the amp is the "noiser" component in the signal chain, keeping the gain (or volume) down on it, is the way to go...

confused yet?

 

Thanks for the input everyone... now I have a lot to think about while I'm saving up some cash...

 

If you're a NOOB to car audio any additions to your sound system will be great for you.

Idivinag breaks it down for you very thoroughly and technically, and also precise.
But honestly unless you have experience in car audio or are an installer, you really wouldn't notice these differences.

Just make sure you get a good amp(s). It is a nice place to start in building your system even if you can't afford to change the head unit yet. Remember, you could always use the stocker with a high lo convertor.