Date: Fri, 26 Jul 2002 09:25:36 -0400
Reply-To: David Brodbeck <gull@CYBERSPACE.ORG>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Brodbeck <gull@CYBERSPACE.ORG>
Subject: Re: ignition buzz in speakers on 88 vanagon
In-Reply-To: <1a5.5a6ef1b.2a712e99@aol.com>
Content-Type: TEXT/PLAIN; charset=US-ASCII
On Thu, 25 Jul 2002, Frank Condelli wrote:
> Then while futzing with the radio I notice that when the radio is not
> installed in the dash but plugged in and working there was no buzzing. Ha,
> what's this all about ? So I decide to put some electrical tape around the
> perimeter of the opening in the dash and around the edge of the radio to
> insure there is no contact between the radio and the van body. Also need to
> insure the rubber grommet for the rear locating pin is there also. Shoved
> the radio back in place and VIOLA ! no more buzzing.
This is a classic "ground loop" problem.
Your radio was grounded at *two* points -- the power ground, and the case.
Unfortunately, there are a lot of metal joints and such between those two
points, resulting in a voltage difference. Current can flow through the
ground wire, into the radio case, then back through the body. If there's
buzz or something similar superimposed on that current, maybe from
something else grounded to the body, it will be induced into the radio's
circuitry.
When you're using an external amp, you can get yourself into the same
trouble if you're using shielded line-level cables to connect the radio to
the amp. The amp will be grounded at one point, the radio at another, and
the two grounded cases are connected by the shield in the cable. The
result is noisy current flowing through the shield, that induces noise
onto the center conductor. This can be fixed with a ground isolator from
a car audio shop.
Hope this makes sense. It's a bit counter-intuitive until you realize
that a 'ground' at one end of the van may be at a different voltage than a
'ground' at the other end, especially if there's a heavy current flowing
through some of the ground wiring or body. Any time there's a voltage
differential between two points and you connect them with a wire, current
will flow, even if they're both supposed to be 'grounds'. ;)
_ _
__ _ _ _| | | | David M. Brodbeck (N8SRE) Ypsilanti, MI
/ _` | | | | | | +-----------------------------------------------------
| (_| | |_| | | | @ cyberspace.org
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