I need some help in a BIG way! I have a whine that is only heard when I have RCA's connected to my crossover. If I disconnet them from the Xover and run them directly from the HU to the amp there is no noise. I thought it might be the cables so I got a twisted pair and tried again. No help. I think it may be the Xover. Anyone ever had this problem? Any suggestions. My Xover is an MTX RT-X01A. BTW, Everything is properly grounded (moved that several times also).

Sorry, their power supply sucks then.

Nakamichi 45z & Audio Control Four.1

I've moved the ground around.

They're both sharing the same +/- now from the factory radio power.

...AND NOW, I have a power-filter installed!

Hell, what else do I have to do to get rid of it?! (my guess is looking elsewhere for power...or a better noise filter...)

It's not so bad if I bypass the Four.1, but it's still there. The RCAs to the back are clean, and the amp power is clean. no noise from either.

I was thinking of trying the dreaded ground-loop isolator... ...but Radio Shack was out ;)

only coming from my amp.. turned out my amp was fried.

Y would say I need a noise filter only on the x-over when all the amps run off the same power wire in to a distro block? I was thinking more along the lines of something being wrong with the X-over itself. My RCA's going into it produce no feedback (whine). Just the side(s) coming from highside to the amp does.

Ask yourself "Self, from whence cometh alternator whine?" Answer: either radiation (through the air) or conduction (through the wires).

Radiation will be a problem with unshielded low-level high-impedance circuits. I'd guess that most of your components are neither unshielded nor high impedance. There will be both an electrical and magnetic component to the unwanted alternator field. Playing with aluminum foil shielding of unshielded components will help knock out the electrical component, but only a ferrous metal shield (steel, lead, mu-metal) will affect the magnetic component.

My guess is that the alternator whine's getting into your system via conduction. The usual suspect is ground return paths that are shared by low level signals and high "DC" supply current.

("DC" current in a car to some degree has very fast rise time voltage spikes riding on it. These spikes are created by the switching of the diodes within the alternator and are heard as alternator whine.)

When DC supply and low level audio circuits share return paths, these spikes will -- nay, must -- enter the audio circuits. The cure is to force DC return current to follow its own path, and audio signals to follow its own path.

Step one in troubleshooting conduction interference would be to look closely at your DC supply path. Is it (or CAN it?) at any point flowing on an audio cable or its shield? As a test, try running dedicated plus and minus cables directly from the battery (which functions as a capacitor and thus suppresses spikes) to the amp. Don't use chassis ground for this test -- temporarily electrically isolate their metal cases from the car's metal.

Step two in troubleshooting conduction would be to make sure that you're not allowing "DC" current to flow on your audio cables' shields. Try lifting the shields' grounds at one end. (You may need to find shielded cable that allows this. The good stuff does.) First try lifting the shields' grounds at the source end; then try lifting the cables' shields at the load end.

Caveat: A "noise filter" can be almost any collection of electrical components: low pass filter, transformer, capacitor -- who knows? If it's designed to be in series with the DC power line, it's prolly a low pass filter composed of a series inductor(s) and one or two capactors to ground. If it's in series with a signal line, it's prolly a transformer, to provide DC isolation. (Placing a "noise filter" in series with your audio cables will in some undefined way affect the audio signal that passes through it.)

HTH.

dude, I hate to sound like an idiot, but what the Hell did u just say? You totally lost me on this. Let me tell you what I have done thus far and maybe you can aide me better. I tried a noise filter. It did not work. at 2000 rpms I can here the whine. And yes, it is from the alternator. I removed the cables from the xover and ran the cable coming off the HU directly to the amp and I got no noise. I have all the amps and xover running to a distro block. But the prob only seems to be coming from the Xover. No xover, no noise......can there b something screwed in the xover to make it pick up the whine?

. . . especially the parts regarding the importance of separating current return paths for DC supply from current return paths for low level audio (and radio, for that matter) signals.

I tried to both explain the root causes for alternator whine problems, and suggest troubleshooting methods for isolating the problem. Did you try my suggestions that you lift the grounds from one end of the signal cables? How about temporarily trying dedicated + and - DC supply cables, isolated from chassis ground?

These are standard troubleshooting methods that will be useful regardless of environment. (I spent years succesfully troubleshooting military communications systems -- fixed, mobile, shipboard, airborne -- for their manufacturers.) They're exactly what I would try were I in your shoes.

It sounds to me as though your crossover may in some way be part of the DC return path. Try temporarily isolating it from chassis ground, and making sure that DC return current can't flow on signal cable shields that connect to it. (You do this by lifting one end of the cable shields from ground on all cables that connect to the crossover. Look at many top quality prefab car audio "RCA cables" and you'll see that it's possible to isolate one end of the cables' shields from ground. I'm sounding like a broken record.)

I'd guess that somehow your amp's DC return current is flowing through your crossover. Prolly through the cable shield that ties your crossover to your amp. You must (1) interrupt this current and (2) provide a nice low resistance return path for your amp's DC return current (from your amp's DC return terminal, maybe labeled "-", to your car battery's - terminal). Examine the ground that you've provided for your amp. If you were an electron that needed to return to the car battery's negative terminal, how easy a path has the installer provided? Has the installer carefully scraped paint away from the hole that provides the chassis ground connection for the amp? Temporarily try using half a jumper cable from the amp's negative terminal to the car battery's negative terminal.

I doubt if the crossover itself is at fault. In most systems, naieve installation, leading to undesired ground loops, hum, noise, etc. is the culprit.

If you still don't understand these ideas, it may be helpful to review basic DC and AC circuit theory. Sorry if I haven't helped.

I sorta understand some of this. To an electronics expert this is easy, but to an electronics novice, this is greek. I'll move the + and - lines and run them to the battery, but the only problem is I can only hear the whine when I drive and go over 2000 rpms. So, I have to run new lines to the battery. Im not sure what you are referring to when you mention lifting the grounds from one end. Explain that further if you can.

By "lifting the ground" I mean remove the connection between cable shield and chassis ground at one end of the audio cable. (Leave the other end of the cable's shield grounded.) Many top quality cables allow you to do this; cheap ones don't.

Normally, you'd think that grounding a cable shield at both ends of the cable would be desirable. The problem with this is that when you ground both ends of a cable's shield, you also provide a nice path on the shield for currents (such as your noisy DC supply's return current) to flow on enroute from the amp's "-" terminal to the battery's "-" terminal. When these DC supply return currents flow on your audio cables shields, any voltage spikes on the DC supply will be induced onto your audio cables' center conductors and will be heard as alternator whine.

That's why I suggest that you remove the ground from the shield at one end of the audio cable that runs between your crossover and your amp. Don't worry about degrading the effectiveness of the cable's shield; as long as it's grounded at one point, it will provide an effective electrostatic shield.

The general idea is to force your DC supply return current to flow on its own path, separated from your signal paths. If the currents travel on common paths, you will have problems with alternator whine.

As far as running new DC supply lines, you may be able to just use battery jumper cables temporarily, while you're testing. My guess is that the "+" side of your DC supply is fine but that there's a problem with the (often neglected) "-" side. While you're looking at your installation, examine closely your amp's ground cable and where and how it's fastened to your car's body/chassis. You want to provide as short, fat, and direct a path as possible from the amp's negative terminal all the way back to the battery's negative terminal. Pay special attention to the quality of the connection between your amp's ground cable and the car body/chassis, and to the path between this ground connection and Audi's ground connection near the battery where your amp's return current must flow back to the battery's negative terminal.

At least some Audis have galvanized bodies, which can make it difficult to achieve good low resistance ground connections. Search this and other Audiworld forums for more info on this.

Let me know how you fare.