Alternator noise to power AMP

Huw Powell audi at
Tue Apr 5 18:51:15 EDT 2005

> As you predict - disconnecting the shield wire amp side makes no
> difference.

I meant to say this earlier, but I suspect the wire you are referring o 
has nothing to do with grounding or shielding - if the RCA cables were 
intended for auto use, they may have had an extra conductor to serve as 
the amplifier switching lead.

The shielding itself will always be under the insulation and completely 
around the inner core.  On simple cables, it is also the "-" conductor 
and is connected to both plugs.  This can lead to ground loop problems, 
especially in a car.

"Directional" line level cables have two conductors in the center for 
the signal, and a shield that is only connected (internally) at one end.

> The amp was already wired directly to the battery both + and ground.
> I ran a separate ground to the chassis ground point in vicinity/trunk
> and back to the amp so now it connects both to battery ground
> directly and the chassis ground nearby - this also returns back to
> the battery through a different path in the car.  This made a
> significant reduction in the whine, but it is still present.

Try grounding the head unit to the battery directly, also.  I deally, 
everything should be grounded to one place, and only one place.

> The amp still "clips" and I am beginning to believe that a cap may be
> in order.

That sound like a weird band-aid.  How much power is the amp supposed to 
generate?  You mentioned a 10 ga ground lead, that's good for about 300 
watts at 12 volts.  Have you measured the power supply voltage on a fast 
acting meter at the amp while it is running hard?

> I still need to check the shield ground at the head

See comment above...

Huw Powell

More information about the quattro mailing list