AudioControl SA-3052A, Руководство по эксплуатации

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SA-3052A Owner’s Manual
6-9
®
AMPLIFIER Noise like a nasty buzz, that isn’t affected by engine speed and is
usually affected by some or all of the system controls. High pow-
ered amplifiers sometimes cause problems because the DC to DC
converter inside of them radiates EMI (electromagnetic interfer-
ence) into the electrical system of the car. Sometimes (especially
when the units are mounted on a board in the trunk) the manufac-
turer will leave the chassis of the amp floating (not connected).
This turns the amp chassis into an effective antenna. Connecting
it to the autobody ground will turn the amp chassis back into a
shield, which is what it should be. Some amplifiers have a switch
to select an internal or external ground for the amp chassis.
Figure 6.4 shows how to bypass the alternator output. It’s important to put the
bypass capacitor as close as possible to the source of the interference. Bypassing other
electrical devices is very similar. Make sure that the ground connection (the vehicle body
is the place to use) to the capacitor is solid and clean. If you have an ohmmeter, measure
the resistance between the capacitor and the vehicle body. It should be less than 0.3 ohm.
Chapter 6 - Getting the Last ¼ dB
POWER SUPPLY
Figure 6.4. Bypassing the alternator output.
Figure 6.5 shows using a series choke and bypass capacitor to deal with more severe
cases of interference. The choke raises the impedance of the power supply system at au-
dio frequencies so that the bypass capacitor can short it out to ground. It’s a good idea to
use a lower capacitance mylar or paper capacitor that is shunted with a generously sized
electrolytic capacitor.
Figure 6.5. Using a series choke and bypass capacitor.