Rockford Fosgate 250.1 Operation & Installation page 48

III. MOVE THE DECK. If you're at this step, it's time to turn your system into an "amplified deck" by temporarily
relocating the deck right ON TOP of the clean amplifier. Then using very, very short signal cables, connect the
output of the deck into the input of the amp and test for noise. Play a zero bit track – silence – and make sure all is
completely quiet.
A. If still noisy, you're in a heap of trouble. We suggest that you try another deck and give us a call so that we can
put your name into the record books. It's a bad car audio day for you.
B. If the deck is quiet, then congratulations, you're on your way to a successful installation. It is now time to
slowly, methodically, reinstall the deck back into its final position. Test for noise each step of the way. If the
noise returns, suspect the signal cables. Forget shielding because it will have only a very, minimal effect within
the audio band. We highly suggest using twisted pair cables or a balanced transmission system for cable
induced noise.
Time for Processors:
By the end of Step III, you should have the deck playing quietly with the amp, with the quiet cables quietly routed. So
it's time to add the signal processors – one at a time – back into the system. Simply repeat Steps II and III with the
equalizer, then the electronic crossover, etc. However, before MOVING THE SIGNAL PROCESSORS to the amplifier,
we highly suggest that you power the noisy process from an isolated power supply rather than the car's +12 volts DC
and chassis ground. Make sure to also connect the turn-on lead to the isolated power supply. If the processor is now
quiet, then it is highly probable that the component has inadequate isolation. Solutions include changing components
or permanently adding an external isolated power supply (Call Autosound 2000 at 209-465-3450 for info on isolated
power supplies).
Summation:
During the design stage of your vehicles, try to avoid using extra batteries and high output alternators. Extra batteries are
nothing but loads as soon as the engine is started and high output alternators usually make more noise than stock
alternators. Also, extra batteries installed in the trunk of a car will ALWAYS force extra ripple current to flow over the car.
Install Stiffening Capacitors
switching power supplies of your amps and minimize the inductive losses in your power wiring. Plus, they will help
your peak system response.
In problem cases, we highly recommend the use of twisted pair cable rather than coaxial cable for RCA leads. This
practice will greatly minimize cable induced noise – especially in four channel amps!
Don't forget that your system is only as good as its worst component. Do NOT use components with inadequate power
supply isolation or you will be asking for problems.
The best electrical ground on a car is the CHASSIS of the car. Do NOT run ground leads up to the case of the alternator
or the negative battery post. Keep ALL ground leads as short as possible.
With properly isolated components, it does NOT matter where the component is grounded. We're sorry to say that with
inadequately isolated components, it matters! With poorly isolated components, different grounds can cause different
noises.
The deck is the signal reference ground for the entire sound system. The deck usually has THREE connections to the
car's chassis: The black ground lead, the base of the antenna, and the metal-to-metal bond between the case of the deck
and the chassis of the car. With three grounds, there is usually NO cause to worry about the ground of a deck.
Amplifiers are usually designed with adequate power supply isolation. This means that it should not matter where a
deck is grounded. (Decks are grounded three times and amps float. This is car audio!)
The more components installed on a signal path, the more chances for noise to enter a system. The more electrical
accessories on a car, the more noise will be produced by the alternator.
This information was compiled from more than 20 years of working in car audio. If you would like more information on
this topic, or any other technical aspects of car audio, please call 800-548-8200 and ask for a subscription to Autosound
2000 Tech Briefs — the monthly magazine for the technically inclined.
® as close to the power supply input of your amplifier as possible. The big caps will feed the
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