Amp ground?

[necros0819]

I need someone to point out to me where I can find the best grounding point for my amp.
The amp is in the rear of my 2007 Mazda 3 hatchback and I screwed it to the side on the plastic piece behind the rear seat.I hooked up my ground on the spare tire bolt the goes through the tire.So far so good but I just want to be sure.
Thanks

[mazdaskit]

Mine is a sedan but I used the rear seat belt bolt been like this over 5 years

[necros0819]

Ok thanks will look to see if that works out best.

[zoomahh]

Mine is a sedan but I used the rear seat belt bolt been like this over 5 years

/| /| This, And if you go with that ground point, as I did when I did my build, make sure the ground cable is as short as possible. Everything I've read and been told say to use the shortest you can. Makes for a better ground

[DLYDRVN]

This is a good mounting point, but your best bet for a solid ground is to use sandcloth or a fiberglass bristle burnishing tool to remove the paint under the bolt so the ring terminal makes complete metal to metal contact. I threw a little carbon conductive paste under mine, but that's optional.

As far as length goes, assuming the chassis is a near to a zero-resistance ground plane as is practical (it's not but, we can't do better...) then really, lets look at some numbers:

Ohms Per 1000ft:
8AWG - 0.6282
4AWG - 0.2485
2AWG - 0.1563
0AWG - 0.0983

Which means the resistance per foot of even 8AWG (About the smallest gauge you'd ever use for grounding) is around 0.000682ohms.

The difference between 1ft and 10ft can be ignored _ at the lengths we are using and assuming you've selected the correct AWG for the current you will be drawing_

Anyone who tells you differently is mistaken and doesn't understand basic electrical physics.

The biggest weak point in your system will always be your connections. Make sure your crimps are solid (solder if you like), and that any mating surfaces are free of paint and corrosion. Using carbon or silver conducting paste or any conductive corrosion inhibitor will get you much further ahead than worrying about how many feet your grounds are.




/| /| This, And if you go with that ground point, as I did when I did my build, make sure the ground cable is as short as possible. Everything I've read and been told say to use the shortest you can. Makes for a better ground

[zoomahh]

This is a good mounting point, but your best bet for a solid ground is to use sandcloth or a fiberglass bristle burnishing tool to remove the paint under the bolt so the ring terminal makes complete metal to metal contact. I threw a little carbon conductive paste under mine, but that's optional.

As far as length goes, assuming the chassis is a near to a zero-resistance ground plane as is practiycal (it's not but, we can't do better...) then really, lets look at some numbers:

Ohms Per 1000ft:
8AWG - 0.6282
4AWG - 0.2485
2AWG - 0.1563
0AWG - 0.0983

Which means the resistance per foot of even 8AWG (About the smallest gauge you'd ever use for grounding) is around 0.000682ohms.

The difference between 1ft and 10ft can be ignored _ at the lengths we are using and assuming you've selected the correct AWG for the current you will be drawing_

Anyone who tells you differently is mistaken and doesn't understand basic electrical physics.

The biggest weak point in your system will always be your connections. Make sure your crimps are solid (solder if you like), and that any mating surfaces are free of paint and corrosion. Using carbon or silver conducting paste or any conductive corrosion inhibitor will get you much further ahead than worrying about how many feet your grounds are.

Wow thanx for that info man...and your right I don't know squat about electronics except what I've always been told re; length of ground cable. Noone ever said any diff so I figured that was the rule.

As far as your comment about crimping goes...hmmm I'm having an irritating issue with my rear speakers not working properly. Sometimes it just comes on...then it cuts out.. And my connections are butt connections (crimped) I'm gonna look at that first chance I get...

My apologies to OP re; length of ground cable..was only going by what I was always told :p

Anyway B O T :)

[DLYDRVN]

Hey man, not directed at you at all! It was more a generalized statement ;-)

I just hate to see a lot of misinformation passed around thats stated as gospel (not what you did, you qualified your statement).

Just want to make sure I correct it if i can. And of course if I make errors, I like to research and figure out the right answer so that I don't become part of the problem ;-)




Wow thanx for that info man...and your right I don't squat about electronics except what I've always been told re; length of ground cable. Noone ever said any diff so I figured that was the rule.

As far as your comment about crimping goes...hmmm I'm having an irritating issue with my rear speakers not working properly. Sometimes it just comes on...then it cuts out.. And my connections are butt connections (crimped) I'm gonna look at that first chance I get...

My apologies to OP re; length of ground cable..was only going by what I was always told :p

Anyway B O T :)

[DLYDRVN]

Double check those speaker crimps too. Properly done crimping is as good as a solder joint. Poorly done crimps are a recipe for disaster. Make sure you use appropriately sized, quality butt crimps, and a good crimping tool appropriate for insulated crimps. Also make sure your crimp tool is perpendicular to the joint in the crimp sleeve. If the crimp crushed the sleeve sideways it'll totally loosen up over time.

I like using the transparent insulated crimps so there's no mistaking where the joint is located.

[zoomahh]

Now I'm REALLY gonna check my crimp connections :P

[Dave_The_BMXER]

Hmm. Didn't know the length thing was essentially an urban legend.

[DLYDRVN]

Don't get me wrong, it's not like it's a bad idea. I mean sure keep them as short as is convenient, but really there are far greater issues in your power delivery system, let alone the entire audio system to be focused on.

I suppose the argument could be made for higher potential for ground loops or noise, but I'd need to see some data on that before I'd go out of my way to worry.

[SomeGuy]

Eh, you can do better than the chassis for a ground if you want....run dual lines for both positive and negative to the back. The resistance of straight copper wire will be less than the chassis and also remove a bit more potential for noise.

[DLYDRVN]

Actually the cross sectional area of the car chassis is effectively larger than any practical wire gauge you could run, and assuming your chassis connections are good and solid provides a much lower resistance than a second run of wire (as close to 0ohms as possible).

But more critically because running a second line to the battery for your amps would remove the amps from the common ground plane that everything else in the car (deck, processors etc...) you've now created a second ground reference and your potential for noise goes way way up.

If you wanted to be _super_ anal, I suppose you could isolate and star ground all of your audio gear, but the performance advantage (if any) wouldn't be worth the effort and cost involved.

Even if the car chassis resistance _were_ higher, it's far more important from a noise perspective that everything have a common ground reference than paths of varying resistance, even if those resistances were less.


Eh, you can do better than the chassis for a ground if you want....run dual lines for both positive and negative to the back. The resistance of straight copper wire will be less than the chassis and also remove a bit more potential for noise.

[SomeGuy]

Depends on the chassis, I remember one or two back when I was installing that the rear portions (trunk and such) had piss poor grounding ability and we couldn't find anything suitable, dodge neon comes to mind. We ended up doing a second battery in the rear along with dual runs of 0 gauge.

Also, a lot of stuff in the engine bay is grounded to various points (not direct to the ground point of the battery on the chassis) so running a second run back actually doesn't hurt noise as far as I've seen. Like why else would the big 3 work so well, you're adding additional ground points to strengthen circuits that through the chassis are weak.

That said, common grounding of the entire audio system would be preferable, so tieing in the head unit and all amps to that ground run would be ideal.

[DLYDRVN]

Ill grant that depending on the design of the car or condition of the chassis that you could have a difficult time getting a solid ground, but I suspect that's the exception, not the rule.

A big 3 upgrade adds additional or larger ground points to the chassis, not the battery. Thbattery to chassis ground is one of those 3. The idea is to add additional flow to the common ground plane (the chassis) because the stock wiring and ground connections are usually insufficient to handle the extra current flow in medium to large sized audio installs. But you're still increasing the integrity and capacity of the grounds _to the chassis_ which is still being used as the common ground plane.

Moving off a commmon ground and running a wire straight to the battery isn't a guarantee of more noise, but it's definitely increasing the possibility.


A fully isolated star grounded audio system back to the battery would be perfect, I agree, but a fair amount of extra effort for probably minimal gain. All else being equal, the chassis acts as the centre of the 'star', with a single connection to system/battery negative.

I hope I'm not being contrary. It's just that I design and implement grounding systems for audio circuits in my business, so I have some experience with bad and good ground implementations and the results of such. Just imagine we're having this conversation in your garage post install ;)

I think overall my point is just that in the grand scheme of your audio system, worrying about star grounding, length of grounds etc... Is a minor detail. There's are so many other big things that should be focused on first that will have a far greater effect (connection and termination integrity, proper cable sizing, big 3, gain staging...) that to me I'd just make a solid ground to a convenient point and move on :)

[SomeGuy]

Riddle me this then...the negative battery terminal has a short 1 foot or so wire direct to the chassis, so what difference does running another conductor to the battery rather than chassis make in terms of a ground? To me it is the same ground. I'd also expect that running a heavy copper conductor to the trunk would do better than random sheet metal, plastics, composites, etc attached together with spot welds. I think it would be an interesting experiment to measure the difference in resistance.

I suppose best of both worlds would be to tie the extra ground run back to the chassis in the trunk with a distro block?

It's an interesting discussion :) not arguing...and my car audio knowledge is extremely rusty, I haven't done installs in years.