Audio problems

matthew-m · 10-26-2003, 06:32 PM

I have a 97 328i with a complete aftermarket stereo, which has an "audible tachometer". The system doesn't even have to be on! The noise is always there, until I unplug the RCA from the x-over or deck. I have tried wiring the Nakamichi deck directly to the battery (power and ground) and the other components are also wired directly to the battery. I have re-run the RCA's and no change. I also tried lifting/floating the audio ground within the x-over with no change. I even tried putting the deck in the back to see if the computer was the cause. What is really confusing me is that I tried a portable CD player directy to the amps, x-over and just after the deck (using the RCA's in their original place on the passenger side) and each time it eliminated the noise. It doesn't seem to matter that the RCA's pass by the engine computer and the main battery cable on its way to the back. I have also tried a couple different decks. Any suggestions?

System: Nakamichi CD700 and MB70, Monolithic Sound PEQF and Class A 25x2 amps (3), Rane/USB AC23 3way X-over, Kimber PBJ RCA's

blkongry · 08:29 PM

Whoah, I missed that... you have tried a couple different decks and '???' Was the noise still there? Hmm, and even with the system off, you still get an audio response correlating to the engine rpm? Goes away and is clean with the engine off, but ignition turned on?? Okay, there is some piece of the puzzle missing here. If you tried each section of your system discretely, meaning patching in the portable CD player through the RCAs, and the system is clean, but then you patch in the Nak deck, and you get noise... sounds like the deck. If you don't get any noise with the portable, you don't get any noise with other head units, but you get noise with the Nak deck, then I would say for some reason your Nak deck is picking up RF from somewhere in the system. You said you tried putting the deck in the back, away from any components, but you still get noise? And it follows the RPMs? Weird. Either the deck has something wrong and is hyper sensitive to RF interference, or there is something else you keep doing in the setup that seems common place and you aren't catching it. Nak systems are pretty high-brow stuff... usually well insulated and clean.

So, let me know if the other head units you tried gave feedback noise too, or if it is just the Nak deck. Also, is the system noise free with the engine off? Have you tried bypassing the cross over and run the RCAs straight from the head unit to the amps? (or is that what you mean by 'rerunning the RCAs').

One other thing could be a wire on one of the speakers that has slightly shorted (a ground would be the culprit... a hot wire would give some serious noise). It may be something odd meaning the portable or other decks are not as sensitive to picking up the feedback, and the Nak deck is. Lastly, have you tried putting a filter in the power lead? It may be enough to cure the problem.

You've got an odd problem there. It sounds like you've checked the components in the right way (discretely, one-by-one). It's just, from what you have written, hard to tell exactly what works and what doesn't (still not clear on "the system doesnt' even have to be on"... you mean you get noise with everything completely turned off, but the engine running... or do you even get humm with the engine off? Does the noise go away in the off mode when you disconnect the RCAs?). More info would help.

matthew-m · 10-28-2003, 01:44 PM

The system is noise free with the engine off. The noise always corresponds to engine rpm. When the engine is running and I turn off the system, the noise still occurs. The noise stops if I unplug the RCA's at the head unit or crossover, system on or off. I have tried bypassing the x-over and going directly to the amps with no change. Different Nak (CD45 and TD45) decks still produce the same noise. I have tried other brands of RCA's in place of the Kimber PBJ's. I've not tried the filter on the power lead yet. That's next, followed by a ground loop isolater if that doesn't work. I'll look over the speaker wires for a possible short. Any other suggestions?

blkongry · 10-28-2003, 03:55 PM

That's all I can think of. The kicker is that you plug in the portable and the system is clean... then plug in the head unit and you get noise. It's gotta be the head unit. If you don't have any noise with the engine off, then it is probably not a short in the speaker wires. It really sounds like sensitivity in the head unit. Any change between playing CDs and the radio? Are CDs clean, but the radio has humm... or no difference? Hmm, I wonder if you can electronically shield it. I think the in-line filter should help... just a couple bucks at Radio Shack or MCM Electronics. Good luck.

matthew-m · 10-31-2003, 05:54 PM

No difference between CD or radio. I haven't noticed hum before, but it could have been there and I thought it was the horrible reception we get around here. This weekend I'll try the power filter and maybe another brand deck, just for my curiosity. I hope it works....

Wayne 962 · Wayne 962's Garage

Noises like these are very often caused by a bad ground connection somewhere. Check to make sure that all ground straps are connected to the drivetrain, and also make sure that your head unit is grounded as well. As a test try running a ground lead from your deck through the trunk to ground on the battery, and see if that fixes the problem. If it does, then it's definitely a grounding problem, and you know where to look after that...

-Wayne

matthew-m · 11-02-2003, 10:27 AM

I did try running the deck directly to the battery without a change. Yesterday I tried a noise choke and a ground loop isolator with no luck. From what everyone is telling me the problem is power ground related and not audio ground related (since the loop isolator didn't work).
I'm also thinking it may be a radiated engine noise, since I paid a little more attention to it and found the pitch changes with rpm and it is really always there, even with the RCA unplugged from the deck. I tried removing the FM antenna, thinking it was a radiated noise that is getting amplified, and there still was no change. Does anyone know how the factory system sends the signal to the amp - as a speaker level signal or as a preamp level signal? I think BMW may have had an engine noise issue and decided to solve it by using speaker level signal from the radio to the amp, but that won't explain why the CD changer has no noise. At this point I ready to give up and live with it, unless you guys have other ideas I can try before I put this thing back together. Thanks!!!

nut · 11-02-2003, 07:30 PM

how did you make out with this problem? i have done of bmw stereo replacemnets and never had this trouble so i am curious.

thanks

blkongry · 11-02-2003, 08:30 PM

Well, you have a '97, and somewhere between my year ('94) and yours, I am pretty sure they changed the format of the factory stereo. In doing a little research and looking for a pin-out diagram for my factory head unit (I am keeping the head unit and changer, but pulling the line-level into some amps/separates/subs... a little custom with the factory look, since it is a convertible and just to easy to rip-off), I came across a couple articles referencing E36 series stereo upgrades. The articles were key to my year, but referenced a much more complicated factory stereo system on the newer model E36. If this truly is the case, and you can't get rid of the noise, I would start from scratch and do all your own wiring of a custom stereo; meaning new speaker wires, connections, power, etc.. It's a pain in the arse, but you will know everything is done right and where any problems could be.

I have yet to tear into my system, but I've got all info. I'm not too sure what BMW thought they were doing when they developed these systems (especially the cabrio system)... multiple small speakers, no bass, tinny mids and highs... and all the leads are separate and crossed over from the amp... good Lord, haven't they heard of caps and coils over there in Germany??

matthew-m · 11-03-2003, 06:54 PM

Nut - Are you saying my theory could be correct? I haven't resolved the problem yet. At this point I may unplug the system again and start driving the car. It was actually less annoying and definitely more fun!

Theoretically by using an active crossover instead of passives you gain sound quality and use less space. A good single channel 12db/octave passive 2 way x-over can take up 1"x3"x6", while you can easily achieve a 2 channel 3 way active x-over in the same space. Now integrate that into the amp and you save even more space.

I've always thought the system produced a respectible amount of bass. I thought I was going to reuse the factory rear speakers as subs (since I remember them being just perfect for my tastes) but I'm seriously reconsidering that original plan. I think I will spend next weekend wiring everything directly to the battery and totally separating the system from the factory wiring. There goes more money into this thing...

One more question - How are you guys positioning your front speakers? My current driving position has my knee about an inch from the lower dash and 3 inches from the door if I force myself to sit that way. I sit very upright with the seat at its lowest position and the back as straight as possible. I had planned to put a 4" and tweet where the dead pedal is, but I've noticed everytime I move my leg the tonality changes. Any other ideas? I really don't want to cut the door panel but if I have to... Has anyone cut the panel and if so how much depth is available?

nut · 11-04-2003, 07:33 PM

Matt,

you have tried everything but re wiring the system seperately from the original harness. strange though because i have done 94, 97 and 98 BMW upgrades with no noise what-so-ever. i also think that it maybe induced engine noise.
i would try another deck before re wiring though, just in case it is the deck, because i assume the factory deck was ok?

as far as the speakers, i found that the stock speakers are fine, i have changed mine to MB Quartz and found them to be too sharp for my liking, i decided to use just the tweeter. i left the stock speakers and tweeters in place and place additional tweeters in the on the doors. i done this by removing the triangular plastic piece, ( close to side mirrors) and attaching the tweeters on them and replaced the triangular pieces back. this adds the highs, ie, symbals ,strings etc, and also add to the looks

just too bad you arent in my city mat,

nut

blkongry · 11-05-2003, 09:16 AM

As a rule of thumb on speaker placement in cars, you want the front speakers as far away from you as possible... this helps balance the system. If you think about it, when you have them in the doors, you are about 8" away from the driver-side, and several feet from the passenger-side. This makes the sound very uneven, and imaging kinda funky. If you can find a way to push them away from you, and give them enough volume, you'll get the quality sound you want. I personally would like to go with Q-logic pods, but they are a bit intrusive.

Lastly, you don't wan to point any high frequency (aka tweeter) speakers towards any glass... glass tends to accelerate the frequency when reflected and it will make the sound very sharp.

Good luck... I hope you can find that noise gremlin in your system.

Clay.0 · 11-05-2003, 07:16 PM

i had a similar problem in my 95' 325. i put in an amp and subs with a 10 gauge power and ground and it hummed. i talked to a friend of mine that worked at circuit city in the car auto section and he said it was a bad ground. i the stepped up the power and grounds to a 4 gauge wire and the humming was gone.

blkongry · 11-05-2003, 07:41 PM

Interesting... a heavier gauge wire helped insulate the noise? Was the heavier gauge wire perhaps shielded better?