Static when using all 4 channels of tuner output
 

I have a question for my audio expert friends out there as I am completely stumped.

I have a 2002 BMW M5. It was originally DSP, but using the helpful directions from members here I removed the DSP amp, added in the additional 2 channels of RCA's, and started using an aftermarket 4 channel amp to power my components in the interior.

Everything works absolutely terrific, and I am thrilled with the results, but always intended to add some bass - so I added a 2nd amp this week and it didn't work.

Here is the issue: I have 4 channels of RCA output that work great when attached to a single amp, but do not work if split between 2 amps or if used with pass through RCA's to a 2nd amp when the tuner is powered on.

Trials:

• When I hook up the single 4 channel amp, everything works great.
• When I then use the pass through RCA's to the sub amp, I get horrible noises that are constant volume and do not change with the volume control. It sounds like terrible whining, even when the engine is not on.
• If I only use 1 set (front or rear) of RCA's w/ the 4 channel and the passthrough to the sub amp then everything works fine.
• If I split the 4 channels from the tuner and attach 2 to the 4 channel and 2 to the sub amp then I get the nasty noise again.
• Strange: If the amps are powered on before the pass through RCA's are connected, then everything works fine.
• Strange: If the amps are powered on with the RCA pass throughs connected (resulting in the nasty noise) and the RCA's are then unplugged then normal sound returns even if the RCA's are reconnected.
• If I provide a 2 channel signal from a different source (Ipod) to the either amp, or to the 4 channel with pass throughs to the 2nd amp then everything is fine.
• Reseting the amps (by pulling the remote turn on wire) has no effect - the entire vehicle (ie. tuner) must be cycled.

I cannot for the life of me figure out why the tuner provides a signal fine when attached to a single amp, but fails when attached to 2 amps in any way at the time the tuner is powered on.

I've already checked the ground and it measures 0.0 ohms from ground point to battery negative (yes, really - wire brushes on a power drill do a terrific job of removing paint!).

Clearly everything points toward a bad tuner, but since it worked marvelously before the upgrade to remove DSP, I hesitant to replace it...

Any help is greatly appreciated!!!

Doug

The only thing I can think to check is that the ground wires in your original radio harness are connected to the audio wiring that goes from the tuner to the amp. In my old 740iL, the two pins for the audio output ground were missing. And, the ground wires for the audio output were tied back in the wiring harness and spliced to the chassis ground. It was done that way at the factory. Here is my post that describes what I found and my fix.

http://www.bimmerboard.com/forums/posts/99394/

Your problem is very unusual, and maybe it is as simple as some missing ground connections in the wiring between the radio and the amp.

Thanks Brian, the thought has occured to me that I am getting power into my RCA's somehow, but I can't for the life of my figure out how.

I do have a + and - pin for all 4 channels and I personally wired them directly into RCA's which obviously then feed to the amps.

The baffling part for me is why the 2nd amplifier would have any impact -- again, everything works terrific when only the single 4 channel amp is connected, but as soon as the 2nd amp gets in the equation, either through the pass throughs or wired directly, I get trouble. But even then, it is only if all 4 channels of RCA are used - if I use any 2 then things work fine.

I don't suppose you know a good amp repair place in Massachusetts? :)

d-

Update:

Obviously there is some sort of power backfeed into the audio system, but darn if I can find it.

I decided to try an experiment today and used a set of Ground Loop Isolator RCA's to connect the 4 channel amp to the 2 channel amp.

The problem still occurs where I get a bunch of static / nasty noise, but only for a very split second and then I get music. I think I also now have alternator whine that I didn't have before, but I'm not positive - have to do an A/B test.

Not surprisingly, I found that the shields/pins of my tuner unit have no continuity amongst them. By contrast, the shield of all channels of my amplifier are connected. I believe that what has happened is that I have balanced inputs from the radio (which I knew) and that the amplifiers I chose that I thought supported balanced RCA's actually do not. My suspicion is that connecting the left and right shields is equivalent to connecting the left and right pins (since the radio provides balanced outputs) and is causing an issue. Using a GLI obviously isolates the shields and seems to eliminate the issue...

I'd be more than interested in anyones thoughts on whether or not what I indicated is a possible explanation...

Doug

Well, it turns out I do indeed have alternator whine, but I also have it without the sub amp.

In fact, irritatingly enough, it isn't a GLI, it is power line noise from the nav unit.

Anyone have any thoughts on how to filter our the noise? I know I can get a 10A filter for the tuner, but don't know what to do with the 40A / 80A amplifiers...

Doug