cyamamot@nunki.usc.edu (Cliff Yamamoto) (05/26/89)
Greetings!
What is considered a "ground"? If a piece of electronic gear is
operated on land in a fixed position, the soil is "ground". But in mobile
(ship, plane, auto) environments is the common/negative connection of the
mobile power supply (i.e. generator/battery) *always* considered to be ground?
With audio equipment, the shield (shell) of the common RCA plug/jack
is "ground". But *where* in the equipment is this "ground" referenced to?
They say to avoid ground loops, one should ground everything to a common point.
Is this supposed to connect the POWER SUPPLY grounds to one point OR connect
the SIGNAL grounds to one point? Or are these two "grounds" the same?
Here's the weird problem. I installed a stereo and amp in my car.
The amp is installed and connected to the battery. This scenario is with the
engine running, amp powered up :
When RCA's are disconnected from the amp, no noise. When I connect the RCA's
to the stereo AND power the stereo with a bench power supply, no noise & plays
fine. BUT by just merely connecting the car body ground ONLY to the ground of
the stereo, I get all kinds of motor/ignition noise.
At first I thought the noise was coming through the 12 V. B+ line. But that's
not even connected in this case! It seems by using the bench power supply,
I'm FLOATING the radio above car body ground; ergo no noise. YET the RCA's
are connected between the amp and stereo. Funny thing was I got a small tingle
of a shock just before I connected the car body and the stereo ground together.
It's hard to believe by sitting in a car you can get a shock by touching the
car body and holding a stereo (which is supposedly "grounded" thru the shields
of the RCAs).
Any info on what "grounds" are SUPPOSED to be or how to fix this problem would
be really appreciated!
Thanks in advance :)
Cliff Yamamoto
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