New Install - Inteference

[Rich j]

I know this has prob been covered but the search could not find exactly what i need to know...

Yesterday i put 2 amps in the front boot of my mr2 and ran the speaker cable and rca leads through a hole near the drivers feet, As soon as i connected it all up i got the loudest interference noise ive herd from a car audio system.
It did change pitch when turning the wheel so part of the problem i guess is the power steering the cables must run past.
The problem i have though is i could not find a hole the other side of the car to put the cables through also is there any other motors that side that could cause the same issue ?
Do i have to install the amps behind the drivers seat ? can someone show tell me where any other motors are that will cause me trouble when running speaker/rca cables near.
I also made the ground wire go to the neg on the main car battery, is this the best way or is it better to ground to under a bolt on the chassis ?

Any help would be great

Cheers

[paul port]

I have found that if the amp you are using has it's signal earth tied to the power earth within the amp.... you will get no end of interference problems.
Most 'quality' amps have floating phono inputs - EG Old school phoenix gold / soundstream and even philips etc.

You can check your amp for floating inputs by simply measuring the resistance from the phono outer conductor to the amp power 0v connection - should be hundreds of ohms. Unfortunately I don't think a simple earth loop isolation transformer will help you.


Honestly, I suggest getting an amp with floating or balanced inputs - and you will find the noise simply vanishes.

Noisiest things in the car are:
Power steering pump (If the noise goes after 30 secs without touching the steering wheel)
Fuel Pump (wires run along the top of the centre tunnel passenger side.
Alternator (Charging wires run down the LHS of the car, the Starter feed runs along the top of the centre tunnel drivers side.

A good grommet out of the way of the PS wiring can be found just above the clutch peddle - unfortunately this puts it real close to the starter feed.

If the amp is in the front, then Amp -ve to Batt -ve is fine.
I have a PG ZPA05 under the front, with at least a meter of cable running back to the battery - thanks to its floating amp section AND balanced inputs - there is no noise. I have an old PG-M50 under the passenger seat - single ended inputs - but again Floating amp section - Still no noise... Both those amps must be nearly 10 yrs old by now!!

Paul

[Rich j]

yeah the amps i have are both good amps and they both sounded fine with no interence in my old car.If i put the amps behind the dirvers seat and run the power cable down the left hand side of the car then the speaker/rca leads down the drivers side where will be best to put the speaker/rca leads through to the front ? where is wont get any interference because at the moment ive got the audio cables going through that hole above the clutch and its picking up interference from the power steering ?

[nutter]

there is a hole on the passenger side of the car, although it's a nightmare trying to find it from inside the car. I used a metal coat hanger and poked it through the hole. then i tied the amp cable to it and pulled it through. I don't get any interference.

[paul port]

yeah the amps i have are both good amps and they both sounded fine with no interence in my old car.If i put the amps behind the dirvers seat and run the power cable down the left hand side of the car then the speaker/rca leads down the drivers side where will be best to put the speaker/rca leads through to the front ? where is wont get any interference because at the moment ive got the audio cables going through that hole above the clutch and its picking up interference from the power steering ?

That's the grommet I use for both speaker and Signal...
Seriously... The MR2 really is just very very noisy...
The only place free of noisy cables is the drivers side past the door.

As said before,
LHS you have the main loom joining the back of the car to the front.
Centre you have the starter motor main feed and fuel pump cables.
Best grommet on the drivers side IS the one above the clutch (Short of making a new one)
The Passenger side grommet passes near the power steering ECU and alternator charging cable.

You may be able to persevere and find a solution with your existing amps just by laying the cables out until you find least noise - maybe even fit a power supply filter to the headunit.

However, in my experience, wether the amp is a good reputable make - and even if it worked fine in another car matters not. Having the phono at the amp tied to chassis / power ground does make things a lot worse.

Good luck,
paul.

[Rich j]

ok cheers for the info ill have a change around and see how i get on.

Rich