[urq] Re: Alternator noise to power AMP

[Ben Swann]

Right huw - it is not really a sheild, but a separate conductor.  The cables
do have some sort of shielding on them - at least the thickness lead me to
beleive so, but no provision to ground the shield, or it is as you say
inherently gournded, but I wouldn't know without dissecting them.  I bough
the cables for this purpose and they are supposed to be low noise, but don't
seem to be much better than the el cheapo ones I had used earlier.

I probably have to make improvement to the power supply at the head.

----- Original Message -----
From: "Huw Powell" <audi at humanspeakers.com>
To: "Ben Swann" <benswann at comcast.net>
Cc: "Thomas Hall" <thomaswhall at yahoo.com>; <urq at audifans.com>;
<quattro at audifans.com>
Sent: Tuesday, April 05, 2005 6:51 PM
Subject: Re: Alternator noise to power AMP


> > 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
>
> http://www.humanspeakers.com/audi
>
> http://www.humanthoughts.org/