Alternator whine is one of the most common problems in car audio. All alternators generate alternating current, then turn it into direct current through a full-wave bridge rectifier. The rectifier consists of several diodes, which are devices that let through direct current only. But rectifiers are not perfect, and when some alternating current passes through anyway, car audio sings like a canary, amplifying whine to maddening levels. Eliminating ground loops, inserting power line filters and isolating metal component chassis are proven ways of vanquishing the noise.
Instructions
Use the Process of Elimination
1. Use 10-gauge wire on your amp power leads, both power and ground. Ground multiple amps separately. Isolate the amp chassis from the car body by running mounting screws through rubber grommets inserted into its mounting slots.
2. Unplug the RCA cable from your amplifier's inputs. Make an input shorting device by cutting a cheap RCA cable five inches from the plugs, separating the leads, stripping the jackets and shorting the center conductor to the ground conductor in each lead. Plug it into the inputs, crank the car, and turn on the amp. If there is no noise, go to the next step. If there is noise, install a power line noise filter: interrupt 12VDC+ down-fuse from the amp, connect the filter's power leads in line, and run the ground lead to the amp's ground point.
3. Reduce the signal chain. If you have equalizers and other processors, bypass them. Using the normal, installed signal line route, make a direct connection between amp and head unit. If the noise goes away, the signal processors need to be power-filtered individually when inserted in the signal chain. If there is noise without processors in line, run new RCA cables over a new route and test again.
Treat the Head Unit for Noise
4. Eliminate multiple ground points. Isolate the head unit chassis from the car ground. Use only the attached ground lead to ground it.
5. Try different ground points for the head unit to reduce noise. Try grounding it together with the amplifier.
6. If noise persists, connect the head unit to an external car battery not attached to the car. If there is still noise, replace the head unit. If noise goes away, your head unit is picking up noise through its power line; install a power line noise filter.
Tags: power line, head unit, head unit, there noise, alternating current