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Discussion Starter · #1 ·
finally got rid of noise in system by upgrading rca cables then after setting the gain with an oscope over a range of frequencies and turning the system i got a high pitch noise again?!?!

thought i get rid of that **** do i need to route the rca somewhere else or is that not the problem
 

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That may be the cause of your problem...

Too long, didn't read: Use tape and a pen to mark where your gains are set. Turn the gains all the way down. Play music at that "max unclipped volume" from the head unit. Increase gains until it's slightly louder than you would normally listen to. Turn the head unit down a little to normal listening volume. Is the noise still there?

It's probably easier to throw some numbers around, just as an example; don't quote me on specifics...

Let's say, for example, that your head unit puts out 4.0V at that "max unclipped volume" and your amp is capable of amplifying that by 10x before it starts to distort. Mind you, at 40V, you're getting, I don't know, 800 watts out of that amplifier. 800 watts of tweeter or midrange in a car will destroy your hearing in minutes, maybe seconds, so you don't run the head unit at "max unclipped volume" for normal listening. Instead, your only using maybe 50 watts, necessitating only 10V out of the amplifier. WIth the 10x amplification, you only need 1V out of the head unit to get the volume you want.

The problem is, noise introduced into the system after the head unit is not affected by the volume control on the head unit, so if for example, you have 0.5V of noise, with 4V of input, the noise is 1/8 of the signal. WIth 1V of input, the noise is 1/2 of the signal... The math of it is, it doesn't matter if your amp provides 2x or 100x amplification, setting the amplification higher than it needs to be, and then providing less input voltage to reduce the volume, in short, maximizes the volume of noise in your system at all times...

Using an oscilloscope to set gains is useful for the SPL folks. For SQ, any louder than "showing off to the ladies while smashed on tequila" isn't very useful. As I said above, try turning your gains all the way down and then only increase them enough to get the volume your looking for.


All that said, is your head unit grounded to the same location as the amplifier(s)?
 

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Discussion Starter · #5 ·
That may be the cause of your problem...

Too long, didn't read: Use tape and a pen to mark where your gains are set. Turn the gains all the way down. Play music at that "max unclipped volume" from the head unit. Increase gains until it's slightly louder than you would normally listen to. Turn the head unit down a little to normal listening volume. Is the noise still there?

It's probably easier to throw some numbers around, just as an example; don't quote me on specifics...

Let's say, for example, that your head unit puts out 4.0V at that "max unclipped volume" and your amp is capable of amplifying that by 10x before it starts to distort. Mind you, at 40V, you're getting, I don't know, 800 watts out of that amplifier. 800 watts of tweeter or midrange in a car will destroy your hearing in minutes, maybe seconds, so you don't run the head unit at "max unclipped volume" for normal listening. Instead, your only using maybe 50 watts, necessitating only 10V out of the amplifier. WIth the 10x amplification, you only need 1V out of the head unit to get the volume you want.

The problem is, noise introduced into the system after the head unit is not affected by the volume control on the head unit, so if for example, you have 0.5V of noise, with 4V of input, the noise is 1/8 of the signal. WIth 1V of input, the noise is 1/2 of the signal...

Using an oscilloscope to set gains is useful for the SPL folks. For SQ, any louder than "showing off to the ladies while smashed on tequila" isn't very useful. As I said above, try turning your gains all the way down and then only increase them enough to get the volume your looking for.


All that said, is your head unit grounded to the same location as the amplifier(s)?
alright thank you do much for that ill give it a go. My head unit is grounded to a factory chassis ground and amp is at a different factory ground.

but when i was diagnosing the noise i had before when i disconnected head unit ground it stayed on and the noise got worse (the head unit was pulled out of the dash too) not sure if this is a problem ? thanks
 

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Yes, that could be most of your problem... If the ground for both devices isn't at exactly the same potential, it will introduce a DC current into the signal path, simple V=IR stuff, and there will certainly be ripple in that DC voltage, a la an AC noise that we can hear... It's always a good idea, in any vehicle, to run an extra ground wire from the dash metal structure to the body itself; clean off the paint, do it right... Everything on the dash will work better... Try that, and if not, then your amps need grounded better...
 

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Discussion Starter · #7 ·
Yes, that could be most of your problem... If the ground for both devices isn't at exactly the same potential, it will introduce a DC current into the signal path, simple V=IR stuff, and there will certainly be ripple in that DC voltage, a la an AC noise that we can hear... It's always a good idea, in any vehicle, to run an extra ground wire from the dash metal structure to the body itself; clean off the paint, do it right... Everything on the dash will work better... Try that, and if not, then your amps need grounded better...
So should i just run a cable from head unit to rear amp ground?
 

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That's the sure-fire way to fix your noise issue.

You could still benefit from adding an short little 6" ground wire from the metal structure of the dash over to the body by where it bolts up. Clean the paint off good; you'll notice the factory didn't...

Edit: You should still check to make sure the grounding point for the amps is clean and tight. Secondly, what's the rest of the ground path to the battery? Most people neglect to upgrade the rest of the grounding "system"...
 

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Discussion Starter · #9 ·
That's the sure-fire way to fix your noise issue.

You could still benefit from adding an short little 6" ground wire from the metal structure of the dash over to the body by where it bolts up. Clean the paint off good; you'll notice the factory didn't...

Edit: You should still check to make sure the grounding point for the amps is clean and tight. Secondly, what's the rest of the ground path to the battery? Most people neglect to upgrade the rest of the grounding "system"...
Why do you recommend grounding the dash metal as well? and i’m getting a 15” sub in soon so i will be doing the “big 3 three” at the same time. thanks again
 

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Manufacturers generally take the cheapest way out, which generally entails everything mounted to the dash assembly being grounded to it, and then the whole shabang grounding through the dash mounting bolts to the body; reduces the # of cavities in the connectors... To prevent corrosion, the body, dash and bolts are all coated in a number of coatings, generally preventing good electrical contact. As the vehicle ages, it only get worse. Adding a short piece of wire takes but a few minutes and costs a couple bucks and can sometimes make a big difference. Rather than putting in all the effort to ground the head unit to the same location as the amps, doing this first may do the trick, and if not, no harm, no foul...

The big three misses the most important one of all... The amplifier driving that 15" sub is going to ground through either the braided strap connecting the engine to the firewall, or that little 10ga wire connecting the battery to the fender...
 

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Discussion Starter · #11 ·
Manufacturers generally take the cheapest way out, which generally entails everything mounted to the dash assembly being grounded to the it, and then the whole shabang grounding through the dash mounting bolts to the body. To prevent corrosion, the body, dash and bolts are all coated in a number of coatings, generally preventing good electrical contact. As the vehicle ages, it only get worse. Adding a short piece of wire takes but a few minutes and costs a couple bucks and can sometimes make a big difference.

The big three misses the most important one of all... The amplifier driving that 15" sub is going to ground through either the braided strap connecting the engine to the firewall, or that little 10ga wire connecting the battery to the fender...
Ah alright i see. I thought the big three was battery to chassis, engine grounds and power from alternator to battery?
 
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