I did read the thread that talks about routing the power from the engine bay for an amplifier. I was wondering if that is really necessary... could the power be fed from the rear accessory plug instead? That's a lot closer and assuming I won't use that plug for anything else, it should be sufficient - or is it? What is a drawback of using this outlet for this purpose?

Second thing: I also will need power for an MP3 jukebox that will reside in the trunk. Is it OK to use the same power source for that as for the subwoofer?

And the last one: since there is no remote turn-on signal coming from the stock head unit, how can the amp be turned on and off? If I would use the rear accessory plug, that is turned on with the ignition key's accessory setting if I'm not mistaken. That'd be OK with me (provided this doesn't result in some noise when the amp is turned on but I don't listen to music) - but would I not get some loud popping sound when the amp is turned on or off? I remember I had this problem once before... was really annoying.
Or is there a better solution for the turn-on signal?

Thanks for the ideas

 

HOLY CRAP dude....your talking about running an AMP...not a cigarette lighter....

NO...the supplied power from the accessory plug is not anywhere near efficient..

You need a straight feed from the battery, through a 30 amp fuse block, about at least a 10 AWG power and ground AT THE LEAST..and this is minimum for a 150-300 WATT system...

Never try to power an amp off of accessory like that...that has about enough awg wire to carry MAX 15 amps...

 

I wouldn't say it can't be done. I know the accessory port is not the best choice for power, but I wired my system that way based on input from another forum member that has been running this way for months with no problems (LRTRX8).

I have a small Class-D amp (350W), which is much more power efficient than older designs, and that accessory port is surprisingly fused at 20a (same as my Alpine Amp). I figured I would try that first, and if I poped a fuse I would bite the bullet and run it up to the battery. It was very simple to wire up that way- just a few feet of cable to get to the trunk, and it hides nicely under the center console. So far so good- I have taken it up pretty loud and it's handling it fine... time will tell I suppose.

(My Install thread:
https://www.rx8club.com/showthread.p...threadid=19906)

I think you just have to look at what kind of equipment you plan on running and decide from there...

-Sean

 

Why exactly? The accessory outlet has a 20 amp fuse as it was pointed out, and I really don't need more than maybe a 100 W amp... we are talking about a mono subwoofer amp only, not a 5-channel monster.

 

Sorry...i come from a Custom shop background and have installed and built many show cars and non-show cars throughout the SE and I'm just a stickler for doing it correctly...and planning for the future...

If you want to wire it up that way it will probably work out just fine for you...you just have to remember....your amp under load will be pulling a constant amperage across the 18awg wire that powers that accessory plug. If in the future you want to go with another setup say to power the Focals and a sub...there would be no way in hell you could get that to work from that small of a lead...100watt amp will work out just fine I suppose for the way you want to run it...I on the other would NEVER do it that way...to me that is lazy but again I'm a guy that does it the right way the first time so I don't have to go back and rip my car apart to do it all over....

 

I completely agree- if the application was for any more than a small mono sub, than this wouldn't be smart. I also agree that if I had to rip into the car at all for this that I would say screw it and do it the right way up to the battery.... however splicing into that acc jack took less than 10 minutes- just 4 scews to loosen the rear center comartment enough to lift it 1/4" and slide the wire in, pop-out the power jack from the front (very smart design by Mazda), and splice. It seems like that power wire was a little beefier than 18awg, too, but I could be wrong. I figure Mazda is planning on people running portable DVD/TV/game systems for back seat passengers (I have one of those DVD-in-a-bag things for the kids myself), which would explain the beefed up cig lighter circuit. I never thought I would say that I miss my Miata's trunk, since it was the size of a loaf of bread, but having the battery back there was really handy for stuff like this.

I'll be the first one to admit it was lazy, but it was also well below freezing in my garage... time was important : )

 

Thanks XeRo and G8rboy... yes, I agree, using the accessory plug for anything more than a small (100W or so) subwoofer amp is not a good idea. But my original question was exactly about that... I know that if I want to hook up an amp to power the speakers, I'll have to route the power from the battery. In that case, I'll need to rewire the speakers too, since I don't think that the stock wiring would work well with more power to the speakers than what the stock head unit can provide. Somebody correct me if I'm wrong...
So, for the sake of simplicity, having JUST the small sub amp running off the accessory power source should be OK I guess.
That keeps things simple until the bigger project (new amp for the other speakers, complete rewiring) happens.

Any ideas about the third question regarding the remote turn-on (or generally, how the sub amp should be turned on and off, without a loud "POP")?

Thanks.

 

Since the acc port we've been discussing is switched on the ignition already, I just made a little loopback wire from the Power connector to the remote connector on my amp (you can see the little red loop) in my pics. I was expecting the POP sound, but it's fortunately not doing it... I've never had a digital amp- perhaps that is damping the sound?

-Sean

 

you can easily wire this to any accessory that is powered once you turn the key to Accessory on your ignition. Easiest way is to get a volt meter and open your fuse block and test what you think will be an accessory function..then splice into that wire for your remote turn on...if you properly ground you shouldn't run into any "pop" when you turn your key.

To answer your ? regarding rewiring...it's best to do this especially since your running a higher end brand (Focal) that requires some nice clean power...When replacing the entire speaker set I ALWAYS replace the factory wiring just because I rather have the better stuff running to the "better" speakers...the same goes with home audio...without getting into the technical aspect of it all cause I'm not long winded like Rotarygod...the best guage wire will give you the best signal resulting in the best sound, as long as it's in line with the power requirements of your supplied power output and the speakers, I.E. 12awg wire won't make a damn bit of difference if your running factory HU and factory paper cones...but as in our case throw some Focal comps in the front and push them with a 150wt amp and you run some 12-14awg shielded wire...that will sound AWESOME!!!

 

I'll be a little long winded here but anything important is worth saying alot about.

Why is there never enough time to do it right the first time but always enough time to do it over again? I'm going to shout this...

RUN A NEW WIRE FROM THE BATTERY TO ANY YES ANY AMPLIFIER YOU INSTALL IN THE VEHICLE REGARDLESS OF POWER OUTPUT!!!

A 20 amp fuse won't just burn out once 20 amps pass through it. You may actually pass 80 amps through it for a fraction of a second. The amperage rating on a fuse is based on this amount over a certain amount of time. Yes a high amount will pop it immediately but this isn't good for a small wire either. You can actually melt a fuse without blowing it and you could do the same thing to a small wire. This is much more likely to happen on the small platic fuses rather than the glass fuses. To do something because it is "easier" or "temporary" isn't a good excuse. It is really only going to be temporary until it malfunctions. The basic excuses will still apply such as "why should I redo it if it is working good now?". Spend the extra 20 minutes on it and run a wire from the engine bay. It is simple and very easy. There are many much more difficult cars out there to run a wire through and I've already shown you where to do it. What more do you want? From personal experience, I once wired up an amp to a small wire tied into the fuse panel. This was back before I got into the industry BTW. The amp worked fine. It was only 150 watts and I had it running to a 30 amp fuse. The small wire under the carpet got so hot that it physically melted. There was tons of smoke and I thought the vehicle was on fire. The wire melted clear through, burning the carpet padding and carpet as well. It also left the charcoal smell in the vehicle for a long time. The fuse never blew! Don't use the fuse size or it's easy excuse. You'll pay for it later.

Just tap into a switched power wire for the amp turn on wire. If you get a pop sound you may need to use a diode to supress the noise.

 

like I said...i wasn't going to get into the whole thing...i got tired of trying to tell people that came to my shop to ask for 'installation help" because they didn't want to pay for my installation charges but they always argued back and forth about the same thing here..."why do I have to run a battery lead when it's just a 150wt amp..." quality always outshines quantity....i just wanna be the "i told you so" guy when you do fry that nice piece of plastic that surrounds the accessory plug...

funny...rotarygod...i did the same thing my first alarm install...i ran a lead wire for testing and with it plugged into the wrong place i had that sucker glowing red hot and melted all the insulation off of it....thank god i didn;t fry something in the car....

 

It may be easy - for you :D - not necessarily for a novice like me. It will definitely take me way more than20 minutes...
But I get the idea - and will take the recommendation from you and XeRo. I'll run the power from the battery (even though I'm not exactly comfortable with drilling a hole into the firewall :p).

But I understand that's the proper way to do it. Thanks again.

 

Rotarygod- i don't doubt any of the potential problems with this setup... you certainly have more experience than I, but until you've worked on a car when it's zero degrees out and 20 in your garage- I'll stand by my "excuse" of being easy and temporary.

I looked at the thread at
https://www.rx8club.com/showthread.p...threadid=16217

...and will likely do this when the weather is more bearable, but I really don't think you can call that an extra 20 minutes of effort to pull the rear seat, glove box, drill, reassemble, etc.

Anyway, I appreciate your feedback and the threads you've done on this topic- it's helped me quite a bit.

-Sean