Thread: Is the amp at fault?

Originally Posted by Tim Lake

I did scrape off the paint yes.

Will, my amps and the crossover are all in the boot (trunk to you US guys) but the PC is in the front under the passenger seat, as is the carnetix unit.
Should I try to run all the earths to 1 distro block or just the amps and x-over (and what fuse ampage)?

Last night I disconnected the RCAs going to the component amp but it was still noisy so I guess the PC is not causing the problem anyway. The head unit earths direct to the battery (which I did a while ago when I thought it was the problem).

Have you tried gong directly from the PC to the amp that is not noisy? If there is no noise, add in the crossover, no noise - add on the 2nd amp. Keep on going until you get the noise again. This will help you determine which is at fault.

Lets ground all the stuff in the trunk to one good ground. There are distribution blocks that dont have fuses. Some call it a ground distribution block. Use that.

Lets try grounding everything up front to one point. You can ground it all to the battery if the cable is thick enough but i want to see all the ground wires come together into one main ground wire. Otherwise just ground it all at a spot midway between your radio and PC. Make sure its a fantastic ground!!!

Originally Posted by Shadow

Because long ground wires pick up more noise than short ones.

Please explain to me how long ground wires pick up more noise than short ones?

Gladly. RF interference is exactly like a radio transmission and a longer wire acts like a longer antenna to pick that up more. Also, a longer wire has a much higher chance of being accidentally run next to a power wire and picking up noise from that.

Originally Posted by Shadow

Gladly. RF interference is exactly like a radio transmission and a longer wire acts like a longer antenna to pick that up more. Also, a longer wire has a much higher chance of being accidentally run next to a power wire and picking up noise from that.

Did you read this: Induced noise/Ground loop trouble shooting guide.

Agreed, a longer wire acts as an antenna. This is an issue when it's part of the input section, i.e. RCAs due to the low voltage and noise floor.

RF is not an issue when it comes to length of your ground wire. A ground wire itself will NOT pick up the type of noise we are talking about here or we would have to insulate the whole entire vehicle (Its a massive ground wire).

The length of a ground wire does come into effect when we talk about ground potential between multiple components. Having a long ground on one amplifer and a short on another MAY cause the amplifier to find a less resistive path for grounding via the interconnects. This will cause a ground loop.

I will bet you that i could use a 15' ground wire and not have a ground loop, and guarantee that EMI will not be an issue (unless i wind it into a coil). I just have to make sure that none of the other components in the system have an easier path to ground.

Shadow, again, you have knowledge of the over-arching guidelines but your explanation for them is off. The rule of thumb for short ground wires is simply to avoid ground loops and not RF interference.

Originally Posted by Tim Lake

Is this the kind of thing I want?
http://www.caraudiodirect.co.uk/prod...oducts_id=4753

I already have the head unit grounding along a very good competition wire (left over from the original install) to the battery so should I splice in the computer and carnetix earths to it?
Then ground the amps and crossover via a distro block.

Thats a massive block!!! Sure that will work. There are cheaper ones that will work just as well.

Yes, try your suggestion of grounding the front to that one cable and the rears to the block. This is not an exact science where i can say it will or not work. I cant see the vehicle You have to try and see.

Originally Posted by parksgm

Will, it seems that given the range of crappy grounding jobs out there, quite a few more people would have issues with alternative grounds through interconnects (and other low resistance pathways) than actually do. I'm guessing that amps must have built-in current limiting circuits on their RCA inputs to prevent just that sort of thing from happening to the novice who attempts to power up his amp with the signal interconnects connected but an insufficient primary ground.

Futhermore, if grounding through alternative lower resistance pathways is so common, why isn't there more advise given about that point in particular in instruction manuals/here on the forums/etc.?

Just curious...

You are absolutely correct. I saw this in another thread and loved it...

Every piece of car audio equipment has some type of noise canceling circuit on the audio input circuit. These input circuits will, ideally, completely isolate the audio's shield ground from the amplifier's internal connection chassis ground. The amplifier's input shield connection (if properly designed) will have virtually no connection to the amplifier's power ground. It should take the signal from the RCA cable's center conductor, compare the center conductor's signal to the RCA's shield (the reference) and amplify the difference between the two. Remember the voltage generated in the body(voltage drop across the chassis from other electrical accessories)? Well if the amplifier used the ground in the rear of the vehicle (where the amplifier is mounted) as the audio reference instead of the shield ground (which is referenced to ground at the head unit's mounting position) as a reference, the voltage generated through the body would become part of the amplified signal. The amplifier would amplify the difference between the signal on the center conductor of the RCA cable and the amplifier's ground (in the rear of the vehicle). Some manufacturers use poorly designed input circuitry which allows the equipment's power ground to have too much of an influence on the signal (not enough isolation). This causes a small amount of fluctuating DC current to flow through the audio shield which allows noise (from the voltage drop across the chassis) to enter the signal path. The 2 ground paths create a ground loop.

Now this is by far more technical than i wanted to get in my discussions but it gives a great idea of what and how. Wish i could have come up with it!