For the last few month I'm having noise problems.
(Alternator whine, etc.)


Been there, done that!

I recently finished a complete, totally insane restructuring of my stereo, and ended up with system noise (I could hear the hard drives and switching noises from the empeg through the speakers) and rather exceptional alternator whine -- at 70 MPH with the music playing loud enough to overcome wind and road noise, the whine was not only noticeable but quite intrusive over even loud passages of music.

The restructuring consisted of replacing the two amplifiers I had (an 8-channel amp for the "small" speakers and a two-channel amp for the subwoofers) with five separate emplifiers, one for each channel pair in the car, each amplifier with its own remote gain control (potentiometer on the signal input) built into the center arm rest. There's more than 150 feet of RCA cable carrying signal from the head unit(s), going back to the equalizer, up to the remote gain controls where it is split five ways, and then back again to the amps.

Lots of opportunity there to pick up noise.

We think the alternator noise was (of course) a ground loop problem. The amps are mounted to a 5/16" almuminum plate which in turn is mounted on hinges screwed to the chassis of the car. It would appear that the new amps were allowing signal path ground through the chassis of the amp and into the aluminum amp rack, because when we "ungrounded" the amp rack, the noise went down considerably.

But the big improvement came when we realized (Doh!) that splitting the input signal five ways at the remote gain controls just [sarcasm] might [/sarcasm] cause a reduction in voltage at the amp inputs. (Try 8/10 of a volt for your signal input and see how good your stereo sounds!).

We put a line driver in the signal path before the 5-way signal split, cranked it up to just below the clipping point on the amps, and... no more noise. Even re-grounding the amp rack left the system listenable -- there is alternator whine under hard acceleration above 3500 RPM (strangely enough, putting the engine in neutral and revving the engine to 3500 RPM produces no whine) but if I didn't tell you what to listen for and when to listen for it you would never hear it.

I'm not claiming that a line driver will be the panacea for every type of system noise, but in my case it certainly helped. (Are you listening, edsmiata?)

tanstaafl.