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From digest.v9.n489 Wed Nov 11 12:28:41 1998
From: Bob Hazelwood <>
Date: Wed, 11 Nov 1998 16:23:27 -0500
Subject: Re: E34 audio problems

Alternator whine is _usually_ the result of a ground loop. In any system, audio ground (represented by the RCA jack shields) and power ground should only be common at one point. That point is usually the head unit. A way to identify ground loop related noise is to feed the head unit signal to an independent system like a portable stereo or a home audio receiver in your garage. Basically connect it to to anything which can amplify the sound but is NOT attached to the car. If you hear the alternator whine in this system, it is coming right into the head unit through either the power lines or it's radiated in. Odds are you will not hear noise in this test. Places where you could accidentally pick up a ground loop are:

  1. Speaker wiring. One of the speaker conductors could be shorted to ground. If this is a "-" conductor, the system may not identify this as a short, but it can cause a ground loop and create noise. Solution: find and speaker wire shorts to ground and isolate.
  2. You appear to have two "head units", the Clarion and the Blaupunkt. Two heads are not always better than one (Sorry). If both manufacturer's assumed a common signal and power ground, then having them both in the system could cause a ground loop. Solution: get power and ground for both units from the same common point. Go to a good, solid point on the vehicle's chassis. Ignore the ground wire in the factory wiring harness.
  3. The unnamed-brand amplifiers you are using may not have well isolated power and audio ground circuits. You would be suprised how many, even from well known manufacturers, don't. Solution: Best- ground _all_ system components to the same point. Bring a wire from the low current components (head unit) back to the ground point for the high current ones. Use a heavy wire (#10AWG or larger) to keep resistance down. Easier - but with side effects: add in-line ground loop isolators to the signal cables leading to the amps. The side effect is that these isolators are typically not perfect sonically, but it's better than alternator whine.

Other things which are not ground-loop related which can cause noise pickup are:

  1. placement of the speaker's crossovers near a wiring harness or other device which can radiate electrical interference.
  2. Ditto with signal cable placement. On E34's usually running them up the drivers side sill works well. I have found the factory wiring is typically the best on E34's, even though it is not shielded.
  3. Bad choice of ground point, which is a problem amplified by vehicles with rear mounted batteries. The best grounding point on an E34 is near the driver's side rear wheel well. Stay away from any point between the battery and the alternator.
  4. Bad alternator or weak battery. This can result in more AC ripple on the power line than the equipment is able to reject.

Business politics prevent me from recommending a dealer on this public forum (don't want to piss off someone who doesn't get recommended) but I will E-mail you privately with a few suggestions.

Best regards,
Bob Hazelwood
VP Product Management, a/d/s/
'93 525i 5-sp. Sharked, BL/ss'd, H&R, Bilstein, etc. BMW CCA (Boston)

> Date: Wed, 11 Nov 1998 07:45:21 -0600
> From: peter newman <>
> Subject: please read e34 audio problems...
> i live in central Illinois. I need to find an audio installer that really knows 5 series BMW's,
> even if they are as far away as Chicago or Indianapolis, or I need specific instructions for my
> installer to get the alternator whine out of my car. here is what i have:
> 94 530i
> stereo:
> nakamichi head unit
> boston acoustics separates at all four corners
> 6 disk changer in trunk by blaupunkt
> 4 channel amp driving separates
> 2 subwoofers in trunk driven by 2 channel amp
> i think the head unit needs to be reground, but i'm afraid this won't solve the problem.
> we've moved the amp grounds and used shielded RCA cables--we even tried running the RCA's outside
> the car, so i don't think that is the problem. i think it is some type of ground problem.
> where EXACTLY should the head unit be grounded to--specific location in the car?
> what about the CD changer, where should it be grounded?
> how about the amps?
> should i only have one amp instead of two?
> if you reccommend an installer, please make sure they have worked on this specific car.
> thanks for your help!!
> peter newman
> champaign, IL

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