Wiring up amps...

Use as thin a cable as possible, then watch your car go up in flames...

I'd wire it up with a sufficient safety margin, ie work out the power draw of the amp, add at least 25% and wire for that.

I'd also put in an additional fuse at the battery end to prevent the magic smoke escaping from the rest of the car just in case.

That was pretty much my thinking. 25A fuse on the amp, use 35A rated wire with a 25A fuse. All the wikkid soundz boyz seem to insist that you need something capable of running 200A...

To some extent it depends on the design of the unit - an amp needs a good low impedance supply to give its best. If it has vast smoothing/reservoir capacitors and the cable run is short the cable needn't be so large as otherwise. Best to wire direct to the battery too.

If you are running big amps then they like welding cable as you can get it cheaper than the stuff ICE stores sell and it's nice and flexible but if you are looking at an amp for a normal car it's a little overkill.

Thats cos they're running stuff badged at 1000W or more so need at least 100A per amp.

Love to know how the makers get their output figure. One amp I repaired couldn't do anything near its claimed output into a resistive load with

13.8v supply. It was a claimed 100w one - but actually struggled to do 25 genuine watts. Which is just as well as car speakers can't handle the power they claim to either. ;-)

They usually claim a peak power for a start, and I'll bet it's very short duration peak at that. Still reckon it's bullshit though.

Well, one common trick is to drive it into clipping, effectively giving you a square-wave out (for a nominal sine input). RMS of a square is twice that of a sine of same amplitude. Of course, you can't listen to it like that, but if all you care about is a power rating...

In the case of speakers, there's nothing in law to say what type of power you quote as long as its accurate so they quote peak power which basically means it'll do what they say at one specific frequency for the minimal possible duration before it blows itself to bits.

And then there's the old peak to peak vs RMS fiasco.

Depends what you're driving. Make sure the cable will handle at least double the power rating of the amp, and make the runs as short as possible. Not only have you got heating to deal with but voltage sag due to resistive effects will screw the sound quality if you're not running big enough gauge cable. Similar problems with the speaker cable, especially if running 2 ohm.

Couldn't stress the above enough either - nothing like a stray 12v cable to really screw your day.

Like my alternator???

25A fuse, 50A cable. Really.

TBH I was indulging in hyperbole when I mentioned welding cable. They do all seem to use something about that thickness (0 awg is the daddy!), whatever amp they're running...