posted
You should probably state the theory as you know it, there's probably 50 different ways of explaining it...
Ground loops are very common problems in electronic design. To my knowledge, a ground loop is just a phenomenon where two different ground potentials create a current in the signal path that's not supposed to be there. Like in a car, when the ground potential at the source unit is different than the ground potential at the amplifier, you can get current in the signals ground lead. If that potential difference happens to include noise from an alternator, you might hear the whine in your speakers... Is that the theory or are you talking about something entirely different?
Posts: 112 | From: NB, Canada | Registered: Mar 2004
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quote:Originally posted by Rrrrolla: To my knowledge, a ground loop is just a phenomenon where two different ground potentials create a current in the signal path that's not supposed to be there. Like in a car, when the ground potential at the source unit is different than the ground potential at the amplifier, you can get current in the signals ground lead.
Read my mind
Quite a while back I thought the wire between the rca cables were for a remote turn on. That's what I used it for in my first 3 or so installs anyway.
My old boss said the wire should be used as a ground in order to eliminate the possibility of noise via ground loop.
After thinking way back it made me wonder: I try to isolate rca's from any power/ground/speaker wire. (I don't use the wire between rca's anymore)
If improper grounds (or extremely long grounds for that matter) can be a source of unwanted noise, how will using the wire between rca's as a ground actually help?
Is that wire just a waste?
Is this a type of catch-22 where you're damned if you do and damned if you don't?
What's the benefit/downfall to having a common ground?
Is the ground loop theory just that? Theory or phenomenon?
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quote:it would all be for nothing without my favorite cawk-smoker NAvi
posted
i have always been wondering what use that little wire between RCA's had? about the ground loop, id have to say that theoretically it is possible for current to flow between two point with different voltage (ground) that are connected... but i know that there are people who can explain this in more technical terms. i am just a software engineer
quote:Originally posted by Crazyjoker2: Would this be a correct stament? Ground loop happens when the AC ground connects to the DC ground.
Interesting.
quote:Originally posted by Pioneer_Phan: id have to say that theoretically it is possible for current to flow between two point with different voltage (ground) that are connected...
Oh yes that raises another good point. From my understanding, sharing common grounds between two things with varying power levels isn't the most ideal.
If that's the case how would linking the ground from the HU to the amp help?
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quote:it would all be for nothing without my favorite cawk-smoker NAvi
Anyways my take on it has always been the one stated before.
I just ran a 12awg wire from the HU to my central grouding point for all of the amps/processing. I have audiocontrol stuff even and no ground noise.
Posts: 986 | From: Detroit, MI | Registered: Nov 2004
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posted
A ground loop can occur for several reasons:
If using multiple grounding points the points have a different potential to TRUE ground (resistance in one of the connections to ground).
If using multiple grounding points an alternating or sporadic signal passes between a set of input conductors and the ground plane causing a low level induced voltage in the signal.
A quite a few more that I won't try to remember...
One thing that it has nothing to do with is AC and DC being grounded to the same point (BTW I'm not bashing anyone there are a ton of misconceptions about noise. Hopefully, I didn't add any with the previous statements - I made a few simplifying assumptions).
It is real or make believe? It's very real. One of the ways it can show up in a system is by oscillations in the speakers with no signal applied (I've seen that one a lot). Another is the noise floor varying at different times (more or less induced current/voltage from a noise source). Another one and this is my favorite... When someone is using the cell phone in the car and you hear it through the speakers (faintly - and before anyone bashes me and tells me that cell phones transmit digitally or at very high freq analog just remember that many times a cell phone is mounted next to the headunit and that there is a speaker in the cell phone that is generating a magnetic field in the audible spectrum).
-------------------- 2004 Saturn Vue Red Line Edition Alpine DVA9860 Alpine H701 MB Quart QTD-25 B&C 6MD38 6.5" Mid B&C 8NDL51 8" Midbass IDMAX (3) MTX 81000D (3) MTX 8302 (2) MTX 6304 (2) Posts: 284 | From: Huntsville, AL (go to BFE and take a left) | Registered: Oct 2003
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One thing that it has nothing to do with is AC and DC being grounded to the same point (BTW I'm not bashing anyone there are a ton of misconceptions about noise. Hopefully, I didn't add any with the previous statements - I made a few simplifying assumptions). ).
posted
The cell phone theory isn't all that untrue, nextel and other iDEN based technologies do transmit in the 800 mhz band. Even when there is not any power being applied to the speaker you can in fact hear it inducing noise. Many times I have used data transmission on my BB which I have in the cupholder below the H/U and it makes noise like crazy. If you think there isn't enough power being transmitted to do it, just think about the 13 year old girls and their antennas that blink... I used to install like 50 of those a day and have taken them apart. They do not have any battery or power source being fed to them, just off of the power that is being transmitted.
Posts: 986 | From: Detroit, MI | Registered: Nov 2004
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posted
another one to throw into the loop. most think of the negative as being the "ground". unless the battery is marked oposite to what it's electrical charge really is, electricity will flow from the - to the +. so really, the + is the ground. i remember about 15 years ago, seeing a write up with illustration, on the flow of a ground loop in a vehicle. but now after i had some schooling, i see that with the true direction of electrical flow, that write up was based on the thought that the + of the battery was the hot side. so looking at it this way, really puts a twist on how/where there is the possibility of a ground loop. but meade's got the best point of one. lmao
Posts: 540 | From: nor cal | Registered: Aug 2004
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so actually there is negative and more negative and the flow goes that way. i remember reading a MECP test book about 5 years ago(might still be the same) where even they spoke of this. i've always been taught this way too. so with this theory in mind, group loops and noise come from differing potential. this would lead the theory to conclude that the negative batt terminal would be the worst place to ground anything since it has the highest ground potential.
i don't really know what the answer is. just remember being taught this.
quote:Originally posted by 95stroked1500: another one to throw into the loop. most think of the negative as being the "ground". unless the battery is marked oposite to what it's electrical charge really is, electricity will flow from the - to the +. so really, the + is the ground.
yup i just learned this the other week in physics. to keep it short and sweet, when there is a voltage difference between the ends of a wire, a force is applied on the electrons and protons in the copper atoms. since electrons are like 6 or 7 magnitudes lighter than protons, they move ALOT faster than the protons(f=ma...with the same force, the lighter particle will accelerate faster).
anyway, the way i always under stood ground loops was like this:
say you have a h/u and an amp, both grounded seperately. electricity always wants to take the path of least resistance. if the h/u has a more resistive ground than the amplifier, the h/u will want to ground itself through the amplifiers ground. Since the rca's are grounded to both the h/u and amp, current will flow from the chasis of the h/u, through the rca's, through the amp's chasis, until it gets to the amplifiers ground wire. since the signal in the rca's is basically just a voltage, the current flowing from the h/u to the amp(due to the weak h/u ground) adds to the signal, and this addition shows up as noise.
quote:Originally posted by 95stroked1500: another one to throw into the loop. most think of the negative as being the "ground". unless the battery is marked oposite to what it's electrical charge really is, electricity will flow from the - to the +. so really, the + is the ground.
yup i just learned this the other week in physics. to keep it short and sweet, when there is a voltage difference between the ends of a wire, a force is applied on the electrons and protons in the copper atoms. since electrons are like 6 or 7 magnitudes lighter than protons, they move ALOT faster than the protons(f=ma...with the same force, the lighter particle will accelerate faster).
anyway, the way i always under stood ground loops was like this:
say you have a h/u and an amp, both grounded seperately. electricity always wants to take the path of least resistance. if the h/u has a more resistive ground than the amplifier, the h/u will want to ground itself through the amplifiers ground. Since the rca's are grounded to both the h/u and amp, current will flow from the chasis of the h/u, through the rca's, through the amp's chasis, until it gets to the amplifiers ground wire. since the signal in the rca's is basically just a voltage, the current flowing from the h/u to the amp(due to the weak h/u ground) adds to the signal, and this addition shows up as noise.
That's a very good explanation of how ground loops cause noise. As long as the ground resistance of the various components are within .25 ohms of each other you shouldn't have a problem. The battery is only a good place to ground when you can find a closer low resistance point because you know it is a fixed .30 ohms resistance. The onyl problem here is that the battery is also the common ground for the vehicles other electrical components as well and you can introduce problems due to ground modulation and EMI. Better to have a second battery near the amplifiers and use it for a low resistance ground. As far as the drain wires on the RCA's they will not prevent loop noise because it is carried on the signal. Drain wires help collect inductive noise and sends them to ground rather than allowing them to be introduced into the signal path. I have a topic on SoundDomain that discuss System Noise, ground loops, and ways to troubleshoot your system and set it up to where you have the best opportunity for a noise free install. Here's the link if you're interested:
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posted
I didnt read this whole thread, but in case it wasnt posted already, the wire in the rcas, if connecterd to the head unit chassis or ground wire, and also the amplifier ground wire, it will give both grounds virtually the same potential and eliminate the noise. upgrading your vehicles grounding system and your ground for your receiver can help too
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