[urq] Re: Alternator noise to power AMP

[Ben Swann]

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

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.

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

The positive wire from battery to the amp is like a #8 wire - pretty big and under 7' long.  I'm pretty sure it has a good ground now.

I still need to check the shield ground at the head - what a PITA to pull this out again, but I may just use the head to power the rear speakers and the amp to power a sub.  Then I'll have plenty of Bass to compliment what is otherwise sounding pretty good.

Thinking about mounting the 10" sub in the spare tire - i can make a round plywood  drum to contain the sub.  This can be removed quickly with wingnuts.  The spare would likely only be used if I had a second flat, as I will be carrying a full size spare on long trips.

Ben
  ----- Original Message ----- 
  From: Thomas Hall 
  To: Ben Swann 
  Sent: Tuesday, April 05, 2005 3:58 PM
  Subject: Re: Alternator noise to power AMP


  I wouldn't think that would matter.  I have a simple test.  Disconnect the RCA inputs to the amplifier.  If the noise goes away you indeed have a ground loop problem, and a ground loop isolator might be the best bet. Some amps are more prone to this.  If the noise does not go away then make sure the amp is grounded good.. Try a temporary grounding point elsewhere in the car and see.  I sometimes have run a direct line to the battery to see if this takes care of it.  If it does then I search for a better grounding point.  Make sure the wires are heavy gauge so they can carry the full current.  8 gauge is good 6 if it is a high power amp, make sure the wire is multistranded.  A heavy guage wire will ensure power flow is there for the amp to generate it full power rating.  If you still clip then you might want to revise you power requirements.  Remember the factory tests their amps without any capacitors in place, so why should you unless you are over drawing the power capacity of the system.

  Here is a link to a RCA ground loop isolator so you can see what i was referring to.

  http://www.sjgreatdeals.com/sises034.html





  Ben Swann <benswann at comcast.net> wrote:
    Well I took a brief look at my wiring on the amp side.  The cables do have a shield ground - it is attached to the amp ground point.  Is this bass akwards.  I don't recall if I grounded sheild at the stereo or if the cable had a sheild ground wire.  So from what i understand so far, it is best to have the radio/pre-amp side of the RCA cable sheilds grounded and not the amp side - correct?

    Hope I don't have to re-run these cables.

    Ben
      ----- Original Message ----- 
      From: Thomas Hall 
      To: quattro at audifans.com 
      Cc: benswann at comcast.net 
      Sent: Tuesday, April 05, 2005 8:47 AM
      Subject: Re: Alternator noise to power AMP


      The RCA circuit of some amplifiers also create a "gound loop" which will also cause this noise.  If beefing up the power wiring fails to remedy the issue, then a RCA ground loop isolator should assist in knocking out the noise.  It is simply a noise filter that inserts in the RCA line between the radio and the amplifier.  This is commonly found at Radio Shack and i have even seen them in Wallmart for a little over $10.00.  Also make sure you are using high quality RCA cables to minimize resistance and to better shield against signal loss and against noise. While capacitors are quite effective they are also very dangerous when charged, I would try the suggested methods before resorting to a large capacitor.  IMHO a capacitor is a kludge against inadequate power to the amplifier in 90% of cases.  I would be happy to assist in helping you isolate this offline if you need it, I have been installing higher end systems since the 80's with over 300 installs under my belt.

      Tom





        > > After recently wiring in a power amp to the rear speakers for my '83 Ur
        > > Quattro, there is a whine being picked up by the RCA inputs to the amp.
        It
        > > is not picked up by the stereo, front speakers, or if rears are wired
        > > directly to the stereo without an amp.
        > >
        > > How can I eliminate this or filter it? I am using high quality RCA
        cables -
        > > don't know if they are sheilded.
        >
        > Try rewiring your grounds so they are all attached to the same place.
        > Also, "directional" RCA cables (shield only attached to ground at
        > pre-amp end) can help. On my coupe I ran ground cables forward from the
        > amps to the shifter mounting bolts, and also grounded the head unit
        > there. On my 90Q I ran a ground wire back from the head unit to a
        > bumper mount bolt in the trunk where I grounded the amp. Neither car
        > has any appreciable ignition/alternator noise, which is nice.
        >
        > > Also, what kind of capaciter would be good to eliminate powere clipping?
        >
        > Although I know people seem to love their 1 F etc. caps in the trunk, a
        > good heavy power/ground cable ought to be enough - your battery is one
        > heck of a charge storage device...



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