Thread: Ewww, ground noise finally isolated, now wut!?

Originally Posted by TheLlama

try getting a noise isolator at wal-mart for $15. I think they are made by Scotsche or something. It is basically two big coils that pass sound from one to the other via inductance. It may degrade sound quality some, but it is a good test. For $15 you can keep it if it fixes the problem and sounds good or just return the thing.

You mean, like the first item I have for sale?

tj!2k4's FS Thread [US/NY/Westchester]

So I need to do what exactly, wills post

"cutting a set of RCAs to a couple inches and shorting the inside wire to the outer shield. Plug em into the amp and turn em on."

make only a little sense to me.

I need to get some RCA plugs (L/R pair) and cut off one end so all I have is 2 RCA plugs and 2 bare wires?
Then what?
IM stoopid about this I guess.

Na, you’re not stupid it’s a hard idea to grasp. Let’s see if I can explain this a little. What makes the actual sound from the speaker is the voltage difference between the positive connector of the RCA (inside) and the negative connector of the RCA (outside shield). Ideally the negative should be at 0 Volts and the Positive will fluctuate from + to – Volts to push the speaker in and out. Now the issue with a ground loop problem is that the negative connector is not at 0 Volts ideally but is rather a slightly positive voltage or is fluctuating. If it fluctuates you will hear a whine change as you rev your car. If you hear a buzzing that means the ground is not at exactly 0 Volts (bad ground). So if two components are reading different ground values say +.5 volts on the amp and +.9 volts on the Head unit, they are both going to get different values when subtracting ground from the Positive connectors, introducing a buzzing or whining noises as it passes through the components to your speaker.

Now the reason why we short the positive to the negative on the RCA plug is to keep both the positive connector and the negative connector at the same voltage. If the ground is fluctuating in voltage, that same change will be sent down the positive part of the RCA cable into the amp. Same voltage on both line means when you subtract them, you get a difference of 0 Volts or silence in the speakers. By doing this, you should ideally not hear anything when you connect a speaker directly to the amp audio output. That’s why they’re called mute plugs cause its like you muted your system.

From there we start to narrow it down as to what might be the cause, your amp, or the rest of your setup.

The reason why everyone is saying to scrap off the paint is because anything that provides resistance (loose connection, wire that is not think enough, etc) will change the GND reference from 0 Volts to a slightly positive voltage causing ground loop issues.

to short out RCAs just clip one end off and connect the wires inside?

oh and if this matters, when you turn the key to start the car (all electronics off, even with the RCAs disconnect but the remote-on wire still to the HU so as to turn on the amp) you hear a WHIIIIRRRR in the speakers like its listening to the alternator turn and rev up?

which is weird because the amp isnt "on" and the HU hasnt told it to come on while the car is starting...so nothing should come from the speakers at all but there is something carrying over into the speakers even during starting.

I got a couple of these lying around:



which gave me this out the end:

yes

where is your "remote on" connected to on the amp. Is it connected to the HU "amp on" wire? Also where is your "remote on" connected to for your crossovers? Same as the amp?

crossovers are passive, came with the infinity components kind of deal.

the "remote on" is connected to the "Blue/White wire which is for 'system control terminal of the power amp or Auto-antenna relay control terminal'" out of the head units wire harness.

HU to amp with a long wire....which could be frayed and shorted to the chassis maybe somewhere...its an old long wire and pulled alot thru the car if I recall correctly...is this starting to make sense or somethign?

Twist all of the wires together to form a muting plug. You will want one for right, one for left.


I wonder if he is getting RFI through the passive crossovers? Just a thought...


I have a 4 ohm speaker on a 2 foot piece of wire. I tinned the ends with solder and use it as my test speaker. If it were me, I would use the plugs and one test speaker. Turn the amp on and carefully attach the test speaker to each output channel, one at a time. If the sound is still there, its the amp. No way around it.

Do you have the amp mounted to metal using metal screws?

if the Blue/White or the frayed old long wire was shorted to ground, your amps wouldn't turn on at all.

Just connect the white and black wire in the middle of the RCA together. The outer one is just a shield and probably doesn't need to be connected to anything.