Rockford Fosgate 250.2 - Manual (Page 47)

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, methodi-
cally, 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 ® as close to the power supply input of your amplifier as possible. The big caps will feed the 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.
– 44 –