High Level Vs RCA & High Level adapters

I've just installed an amp and a hands free phone system on the front
speakers of my car.

The handsfree phone system sits between the iso plug on the head unit
and the iso plug on the wiring loom. It can interrupt the head unit
output on the front speakers with that of the phone.

The iso speaker connections run straight to an amp and into its high
level input. The cable length is about 12ft. The return run to the
crossovers is about 15ft.

I can detect a slight hiss from the front speakers when there are gaps
in the audio.

Would connecting Line out adapters to the speaker output next to the
iso plug then running an RCA cable to the amp be a better setup or
would it make little difference?

TIA

James.

j.stewart@connectdigital.co.uk (James Stewart) wrote in message news:<3e02f1ec.0311210309.57452386@posting.google. com>...
> I've just installed an amp and a hands free phone system on the front
> speakers of my car.
>
> The handsfree phone system sits between the iso plug on the head unit
> and the iso plug on the wiring loom. It can interrupt the head unit
> output on the front speakers with that of the phone.
>
> The iso speaker connections run straight to an amp and into its high
> level input. The cable length is about 12ft. The return run to the
> crossovers is about 15ft.
>
> I can detect a slight hiss from the front speakers when there are gaps
> in the audio.
>
> Would connecting Line out adapters to the speaker output next to the
> iso plug then running an RCA cable to the amp be a better setup or
> would it make little difference?
>
> TIA
>
> James.

In addition:

I've tried running the amp with RCA leads from the head unit and there
is no interference.

I've tried with and without the hands free and there is no difference,
the interference still exists.

I'm also experiencing alternator whine (only with the high level
input).

It appears that the high level cables between the head unit and the
amp are picking up interference. The secondary amp is connected via
RCA and has no interference whatsoever.

I have found a capacitor to connect to the alternator that's meant to
eliminate alternator whine. The device is connected to ground then to
the + ignition switch supply coming out of the alternator. The
instructions say to connect it to the ignition switched + supply from
the alternator. The problem with my alternator is that it is always
live... it has no ignition switched + output. Can I fit this type of
interference suppression device with a constant + output?