95stroked1500

i've followed a few of your posts and you guys definately have an in depth knowledge and understanding in this field. i need to pick your brains. i seem to have run into a problem with pioneer decks, their isolated ground on thier preamp section, and using amps that aren't designed to be fed by a deck using that set up. i have talked with pioneer and a few engineers of amps. pioneer says to ground the shield on the rca's, which so do some others. now these others also say that i have to becareful and not shield ground the rca's on a unit that doesn't run an isolated ground. so educate me on all the how's, why's, and what is going on in these situations.
on another note, i saw where you guys talked about the AC dqx. i've been eyeballing one of these units for a while. what are the ups and downs of them and do you like them?

GPz1100

If i recall correctly (its been a few years since i studied this), floating grounds are used on speaker outputs in amplifiers using a single supply (ie +12V or +14V), vs an amplifier with both types of supplies.

In a dual supply system, there are both positive and negative voltages available for the signal relative a ground (or 0V level).

In a single supply system you'd lose half of the signal if your ground was at 0 V since no negative voltage is possible. Thus, the ground is actually midway between your min (0V) and max (12V).

The reason you won't want to mix the two (floating and common) should be obvious - by connecting the floating ground to a common ground, you are in essence shorting out the driver (amplifier) for that channel.

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I'm sure rich will be around in the morning to clarify this further.

95stroked1500

yeah, the short is what i had in mind. in further digging, it appears that the dual supply set up isn't what is used. but don't quote me on that. in talking with some more in the industry (engineers/manufacturing end) that if it was a common ground (so to speak) it would be possible to get noise introduced because of a ground loop occuring from grounding the rca shield. so in the isolated ground set up, grounding the shield will eliminate noise, turn on thump (if those are related to the shield needing to be grounded), and the issue of smoking the preamp section of the deck or amp that has happened in some cases.

GPz1100

I have never heard of grounding the shielding in the rca's. If it's a floating ground setup, why would you want to do this?

The sheild provides the return path in the circuit. If there is no shield you just have the signal wire, and an open circuit (unless its using chassis ground to complete the circuit.)

Please explain.

ps. Try using some blank spaces .. makes it easier to read..

95stroked1500

i'm still digging so i can fully understand what is/isn't going on in this situation. i have a few concepts i believe i have grasped, but i'm needing some more input to make

sure i have it nailed down. then i'll explain my findings. but thanks for your input so far. and you're not the only one who this is new to. as one of the engineers has never

came across this issue either, and he has been in the industry for over 20 years (as an amp and speaker engineer). but some of the others have.

GPz1100

http://groups-beta.google.com/group/...37e4093c55d089

Good read.. Especially the replies by R Finley

95stroked1500

thanks for the link. doesn't the rca put out an anlog a.c. signal? as using standard rca's in a balanced line system, appears that now instead of just using the center wire for a.c. travel, now when the center is

+, the outside is -? as far as what i belive to be going on here, is like what eddie runner says that they are using the shield for a ground potential, and it isn't getting a

ground in this case (or a good enough one). what i seem to understand so far, is that the design in some amps is to have the ground for this shield, and in others, it doesn't. one reason is something to do with

rejecting noise, internal circuitry, and relying on the deck to provide the ground. but like i said before, i'm going to research some more and make sure i have it down right.

Richiec77

iTrader: (3)

When Common ground is no longer Common. lol That can be a confusing subject.

Don't connect to Common ground. It will skew the refrence ground for the Amplifier's. By doing that you then change the Refrence signals ground and it can then add noise into the system.

What you are explaining GPz1100 is for a balanced line system. It develops it's refrence ground between the potentials. Basically it looks at the 2 voltages and developes it's reference. An audio signal is AC voltage. The biasing circuits for the amplifiers are DC.

Ground for the Signal is isolated from Common Ground. To produce a clean signal, you need a nice flat ground. No bumps on an O-scope if you view it. Should look flat until you zoom in pretty far. (will always have a tiny amount of noise.)

For an Amplifier to refrence the RCA signal, it looks at the difference between ground and the peaks, rises, and falls of the AC signal. If you have a Peak of say 5vAC (DC equivilant of 5v for a short period) and ground is 0 then it will have it's corresponding dB gain. If the Ground has noise in it, and the input peak again is 5vAC, then the output will waver. Say the ground is floating (not steady) around 0.1 to 0.6 vAC then it will change the dB amount accordingly.

That would then look like 4.9vAC or 4.4vAC to the Amplifiers. That change in refrence is the noise. It also changes rapidly.Thus is the floating ground is very noise it will sound like a hum.

I wish I could learn to use Powerpoint. It would make it simple to see. Let me see if I can draw something up.

Richiec77

iTrader: (3)

Ok. Got something made. Not that good, but I'm happy Power point is easy to use.

1 is a good signal. 1 is with a slightly noisy ground. 1 is if the Ground is not good at all. It can shift and completely change the way a signal works. (rare, but can happen)

GPz1100

Several things. My understanding is the following;

By definition, a common ground is when the reference is a single point (or voltage) for all connections (in the context of car audio).

OTOH, a floating ground is when the reference is at a different level than the common ground.

The original question in part was why one should not ground the shield portion of a rca cable.

You said "Don't connect to ground. It will skew the refrence for ground. By doing that you then change the Refrence signals ground and it can then add noise into the system." above.

One can then extrapolate that since the common ground carries all sorts of noise in it, there's a coupling effect of sorts when the common and floating grounds are tied thus adding ripple to the reference and henceforth adding noise to the final amplified signal?

GPz1100

95stroked, Please change the subject of this thread (assuming this is permissible) to something like " Common grounds & floating grounds explored".

Found a few good links explaining some theory on this stuff in relatively easy to understand (relatively ) terms.

Although this is not directly tied to this thread, this info is very well written.

http://www.rocketroberts.com/techart/amp.htm

After reading all that, if your brains is not yet fried, take a look at this link.

http://www.wickedcases.com/tutorials/index.html

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One more to do with more theory on bridging..

http://www.bcae1.com/bridging.htm

Richiec77

iTrader: (3)

Ok. I wasn't too clear in the way I worded it. I understand it, but it's slightly hard to explain.

It should be. "Refrence ground" not "Refrence for ground".

And yes. Floating ground is potential above 0. I should have PM'd it too you for some proof reading. Duoh.

Those are some great reference's you found. That should answer all questions.

95stroked1500

i'll try and change the topic and also investigat those links. i just got off the phone with another pioneer tech and went broader into this subject. he said due to power

supply difference, any manufacturer will tell you to ground the rca shields if you are using an amp that isn't theirs. further more, he said it doesn't hurt to ground the

shield even when you are running the same brand head unit and amp. the shild line is used for ground in these common systems. a balanced line might be something

different, we didn't go into that. also, the rca shield ground can be ran over and connected to the ground at the amplifier. so it's source point will be common to the

amp, which if some use internal grounding on that circuit, is where it would go anyway. thanks for the input so far.

Richiec77

iTrader: (3)

I changed the title for you.