Amp install - fuse and ground question

[mx5red]

I’m preparing to install an amp for dash/knee/sound bar speakers, and a small powered sub linked to the main amp.
I planned on running 4g power to the main amp (fused by the battery), a 600W 6 ch JBl, and splitting 8g power from that line to a small under seat powered sub.

I have two questions:
-Do I just need one fuse, close to the battery from the main 4g power feed? The sub also came with a fuse but it seems odd to split the main power and have another fuse on the line to the sub.
-it says to mount grounds from several amps to the same location, but I planned on mounting the main amp under the passenger seat, and the sub under the driver seat or behind the rear seat.
Is it a big deal to run the grounds from the two amps to two different locations?

Thanks

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[3ffi3nd]

Personally, I ran the power for 2 amps separate to battery, one for sub and another for other speakers. My main reason was the difference in power draw between the 2 amps. The sub amp pulls more and I did not want to chance extra power running to the smaller amp if something were to go wrong. As far as grounding, I think 2 different grounds would be fine, you want the smallest length to the ground. I suppose you could use a power distribution block if only running one line to battery then you would have a fuse on each line.

 

[Radio Guy]

Several ways of looking at fusing. Its main purpose is to protect the vehicle wiring in case of a short but some electronics can fail and draw less current than the fuse rating and sit there cooking and smoking for awhile. Probably best to fuse each amp with the factory rated fuse amperage.

As for grounding its always best to use one common ground point for all audio electronics to avoid ground loops which can magnify alternator whine and other noise. Will the amps interface with existing audio equipment in the truck? If so you might find where the OEM stuff is grounded and consider that point for your new install. That will keep everything near the same ground potential.

The 4ga wire sounds good, I ran that under the back seat of my truck but for high power ham radio stuff. The larger wire can be noticed mostly in the deep bass where lots of power is used, otherwise music is dynamic and rarely a constant tone drawing a constant amount of current from the battery so any big current demand is going to be very brief.

Its common to supplement the bass amp with a huge capacitor to provide lots of instantaneous reserve current for music peaks and capacitor values of 5 to 15 Farads is not uncommon these days. Just be careful with big caps as they need to be slowly charged to your vehicle operating voltage before inserting in the circuit and they must be disconnected when you take the truck in for service.

 

[trloh]

I am working on running amp wire as well and wondering if someone can confirm before I cause issues.

I am coming off the battery to cross over to the easily removed plug near the brake booster. I found that there is a wire loom conduit at the top of the firewall that runs all the way left and right. Inside are some twisted wires.

So the question is will having a 4 gauge 12 volt amp power wire in this area cause issues with some of these wire functions? Any interference

likely to occur? I do not know much about Can-bus and assume that is going on in this loom area.

Thanks

 

[Radio Guy]

I don't believe your power wiring in that channel will interfere with anything and I don't think any wires in that channel will interfere with your sound equipment. I would be cautious running antenna cables carrying receive signals or high power transmit signals bundled with the other wires. I've run some low power 14ga 12v wiring in that channel with no problems.

I am working on running amp wire as well and wondering if someone can confirm before I cause issues.

I am coming off the battery to cross over to the easily removed plug near the brake booster. I found that there is a wire loom conduit at the top of the firewall that runs all the way left and right. Inside are some twisted wires.

So the question is will having a 4 gauge 12 volt amp power wire in this area cause issues with some of these wire functions? Any interference

likely to occur? I do not know much about Can-bus and assume that is going on in this loom area.

Thanks

 

[red/green hawk]

I just added an amp and powered sub. You need 2 fuses IMO. 2 different items drawing power. You can get a multi-fuse fuse box for something like this.
https://www.crutchfield.com/p_142DUDB4/EFX-Delta-Quad-Fused-Distribution-Block.html

 

[red/green hawk]

-it says to mount grounds from several amps to the same location, but I planned on mounting the main amp under the passenger seat, and the sub under the driver seat or behind the rear seat.
Is it a big deal to run the grounds from the two amps to two different locations?

Thanks

There are 2 factory grounds underneath the front passenger seat.
As Radio Guy (his wisdom helped me a lot in my install) pointed out if you don't ground all at the same point you will probably get alternator whine. A ground loop isolator off the head unit fixed my issue if you can't find the head unit ground.

 

[mx5red]

There are 2 factory grounds underneath the front passenger seat.
As Radio Guy (his wisdom helped me a lot in my install) pointed out if you don't ground all at the same point you will probably get alternator whine. A ground loop isolator off the head unit fixed my issue if you can't find the head unit ground.

Thank you for the reply.
I was running some wires today and did mount grounds for both amps at the same place under the passenger seat… I did not know I had to take the head unit into account also
I’m assuming the head unit ground is buried behind the dash?
Part of the bonus of the setup I’m trying is that I don’t have to take the dash apart, though I know it’s a little bit lazy/cheating.

 

[red/green hawk]

Thank you for the reply.
I was running some wires today and did mount grounds for both amps at the same place under the passenger seat… I did not know I had to take the head unit into account also
I’m assuming the head unit ground is buried behind the dash?
Part of the bonus of the setup I’m trying is that I don’t have to take the dash apart, though I know it’s a little bit lazy/cheating.

It's not being lazy, it's smart. But taking the dash apart really isn't that bad of an endeavor. Are you keeping the factory head unit?

 

[mx5red]

It's not being lazy, it's smart. But taking the dash apart really isn't that bad of an endeavor. Are you keeping the factory head unit?

Yea planned on keeping 8.4” radio. My “upgrades” just messed things up and snowballed into adding an amp. I really didn’t plan on doing all this, but I couldn’t go back to stock after cutting up the sound bar and spend more time removing the metra knee pods.

 

[red/green hawk]

Yea planned on keeping 8.4” radio. My “upgrades” just messed things up and snowballed into adding an amp. I really didn’t plan on doing all this, but I couldn’t go back to stock after cutting up the sound bar and spend more time removing the metra knee pods.

Factory head units and speakers have an impedance of 2 ohms. Most aftermarket stuff is 4 ohms. You need an amp rated for 4 ohms to maximize speaker potential. It's going to sound so much better!

 

[Radio Guy]

I measured the factory 4" speakers removed from my truck with premium Alpine upgrade and at 1KHz they are 5.5 ohms. The impedance rises some to about 6.5 ohms above about 5Khz.

Using 2 ohm speakers in a mobile environment would be a mistake requiring larger gauge speaker wire and unusual specs on the amplifier. The stock speakers would be a good match to an amplifier rated to drive 4 to 8 ohms.

Factory head units and speakers have an impedance of 2 ohms. Most aftermarket stuff is 4 ohms. You need an amp rated for 4 ohms to maximize speaker potential. It's going to sound so much better!

 

[kd1yt]

I measured the factory 4" speakers removed from my truck with premium Alpine upgrade and at 1KHz they are 5.5 ohms. The impedance rises some to about 6.5 ohms above about 5Khz.

Using 2 ohm speakers in a mobile environment would be a mistake requiring larger gauge speaker wire and unusual specs on the amplifier. The stock speakers would be a good match to an amplifier rated to drive 4 to 8 ohms.

Agreed-

I've seen photos of the top dash factory 3.5 speakers labeled as 8 ohms, but they also have high-pass/ 'bass blocker' capacitors (basically a very rudimentary but effective crossover at 6dB/ octave), so the 3.5's are only "showing up" [in the load presented to the amp] at higher frequencies. The rising impedance of the 4" [described by Radio Guy] creates its own rudimentary crossover reducing how much power it takes in and makes use of at higher frequencies- so it's mostly "showing up" [in the load presented to the amp] at lower frequencies. So it's not like 4 ohms in parallel with 4 ohms, it's probably more like a net 3-4 ohm overall load per channel, which is pretty ordinary for car audio.

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