17
If the distortion continues, proceed as follows:
s
Clamp the negative conductors (–) at Point 1 of the audio system and attach to engine block.
ª
Check to see if the problem has been repaired.
t
If this does not repair the problem, the auto body must be scanned, while the engine is running, with the
negative conductor of the system until a clear reduction in distortion occurs.
ª
Free this point (= Point 2) and remove remaining underneath protection.
u
Place screw with a large diameter on this point. Clear the area on the auto body around the screw and protect
with auto body grease.
v
Attach all grounding cables or set multiplier on this screw and run to all devices. (
central ground
).
w
Any remaining distortion can be corrected with an LC-filter on the positive cable.
A mill voltmeter (smallest voltage drop ) or milliohm meter (slightest resistance) can also be used to determine the
central ground. The engine block or Point 1 should always be the point of reference.
Digital electronics in the vehicle cause an audible distortion up to the GHz range (interference from wireless
reception and car telephones). The switching power supplies of the amplifiers, digital tuner, and CD player likewise
contribute heavily to the current contamination. All of the distortion spectra appear in the supply lines and are
partially processed in the amplifier output stage. This results in a veiled sound in the high tone range. Output is
already heated in the no-load operation or in the smallest capacity range by high-frequency distortion. The
preliminary input stage of the amplifier cannot differentiate between music and distortion and therefore faithfully
amplifies everything that presents itself at the „pre-in“/or current input
.
In order to dampen this effect, the
optimum is realized at the output stage during the manufacturing process. This is documented by the EU type
approval, whereby test specimens are examined for irradiating distortion and for self-produced distortion. Only
after adherence to the EMD limit values is an E-No. assigned. For the reasons mentioned, the frequency range of
the output stage should drop by at least 50 kHz in order to avoid unnecessary heating. With output stages in Class
A or preamplifiers in Class A higher bias current in the low capacity range makes heating unavoidable and should
not be confused with the described influence of distortion.
The removal of the distortion can only be accomplished through specific measures and requires extensive expertise
in the area of filtering technology for proper installation of the system. Important and useful suggestions regarding
this can be found in the relevant technical literature. Attention to the basic rules for laying cables, central grounding
and filtering of the current feed allows a good basic filtering to be presupposed based on use of quality RCA cable.
Special screening problems, which can vary depending upon vehicle type, must be repaired according to each
individual case directly by the particular specialist.
