CD Changer Controls - Whether you get a CD,
cassette or MD head unit get a model that has CD changer controls, they only cost a bit
more, but give you the opportunity of simply plugging in a changer in the future.
Power - Probably the most overrated feature in head
units. The power on head units is seldom given in RMS watts (see amplifiers section
for definition). Typically a head unit has an output of about 5-7 watts RMS per
channel, while a high-powered head unit goes up to 13-15 watts RMS per channel (even if
they claim 35 or 40 watts).
RCA Outputs - If you are planning to run the
speakers from the head unit's built-in amplifier, you don't have to worry about RCAs, but
if you plan to add amplifiers in the future, get one with a set of RCAs (left and right),
three sets preferably (left and right for front, rear and subwoofer). An important
feature to look for is high-voltage RCA outputs. Typically RCA signals are less than
1 volt. High-voltage RCA signals are 2, 3 or even 4 volts. This allows for
better noise immunity and gives you a higher headroom for amplifier gain settings.
Most high-end manufacturers are selling units with high-voltage RCA outputs which are
frequently used in competition.
Security - There are many security options for head
units nowadays. None of them is 100% effective in deterring theft. Detachable
faces are the most common option. The front part of the radio comes off, rendering
the rest of the unit useless. The problem is that after a while people forget to
take the face off, or simply tuck it under the seat or in the glove box.
Another option is codes, key CDs (i.e. Blaupunkt, Eclipse). If
power is cut off, the unit asks for a code or a predetermined CD used as a key. If
the incorrect code is entered, it locks the radio up, requiring service from the
manufacturer. This has proven to be an inconvenience when the owner loses their code
or forget which CD they used to program the radio. Some radios, such as Blaupunkt
are using a smart card, that when removed, renders the unit useless, but again, people
forget to take it out or lose it causing aggravation to the consumer.
Yet another security protection pioneered by Kenwood is a flat panel
that covers the radio when the ignition key is turned off. While this will fool some
people into thinking there is no radio in, it won't fool most thieves.
FM modulated changers can be hooked up to any radio that has an FM
tuner, whether factory or aftermarket. They use the radio's antenna to introduce the
signal. They are usually simple to hook up and consist on the changer itself which
is mounted in the trunk or under seats, the control box and the display/remote
control. The drawback is that the sound of the CD changer will not be "CD
quality", it will be as good as the FM tuner is. The signal coming from the CD
player has a wide frequency range but the FM tuner limits the signal, cutting the lower
and upper ends of the spectrum.