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Rear Panel
DUAL PRIMARY FUSE
10
In order to accommodate line voltage switching, the power transformer is designed with two prima-ries
that can be placed in series or parallel by means of the line voltage selector switch. Each primary is
individually fused, so there is no need to change fuse values when a different line voltage is selected. It is
important to use the fuse values specified on the rear panel. The fuses are provided to limit current to the
associated transformer primary winding, and protect it from overheating and possible destruction due to
fault conditions in the unit. The trip current values have been carefully chosen to allow reasonable
continuous power output performance, while still protecting the power transformer. These fuses should
not open unless there is a fault in the amplifier circuitry that causes excessive mains current draw. How-
ever, abnormal conditions such as a short circuit on either or both channels, or continuous operation at
overload or clipping (especially into 2-ohm loads per channel or 4-ohm bridge load) can cause the fuses
to open. If this occurs, UNPLUG from the AC POWER source before replacing the fuses, after waiting a
brief period of time to allow the unit to cool down.
overload, first by disconnecting one output at a time, and then one speaker at a time until the bad cable or
damaged speaker is isolated. If the fuses open instantly each time you attempt to turn the unit on, it should
be taken to a qualified Crest Service Center for repair.
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COMBO INPUT CONNECTORS
Input connections are made via the 3-pin XLR (pin 2+) or 6.3 mm plug "Combi" connectors on the rear panel
of the amplifier. The inputs are actively balanced. The input overload point is +28 dBu.
CONNECTING OUTPUTS**
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The CPX4 has twist lock output connectors. Channel A and Channel B may be accessed individually with 2
conductor connectors, with (+) at terminal 1+ and (-) at terminal 1-. A 4 conductor twist lock may be used
on the channel A output, with channel B appearing at termials 2+ and 2-. For BRIDGE mode, use only the
channel A twist lock connector, and the (+) output is at terminal 1+, and the (-) output is at terminal 2+,
which is fed from Channel B output.
HIGH OUT JACKS
13
This 1/4" jack supplies high-frequency output signals from the activated crossover for patching to this
amplifier and/or additional power amplifier inputs. Unlike the low-frequency crossover output that is au-
tomatically routed to the associated channel, the high-frequency output signal must be patched to some
suitable input in order to complete the bi-amped system. This 1/4" jack also provides an unbalanced (tip/
sleeve) output to be patched with single-conductor shielded cables.
40 Hz SWITCH
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This switch is used to activate the LOW CUT filter for the corresponding channel. It is a push-type switch, that
requires a small tool to activate. The IN position routes the input signals through the 40 Hz LOW CUT filter,
while the OUT position bypasses the filter. This filter will cut extremely low frequencies, protecting speakers
from the possibility of over-excursion. The filter low-frequency rolloff is 12 dB per octave. The LOW CUT filter
for each channel will function independently of the crossover function.
CROSSOVER SWITCH (100 Hz crossover)
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This switch is used to activate the 100 Hz crossover for the corresponding channel. It is also a push-
type switch and requires a small tool to activate. The CPX 4 offers two 100 Hz crossovers. These are
designed for use when a subwoofer is added to the system. With the switch IN, the input signals are
routed through the crossover and the low frequencies are automatically sent to the corresponding
channel. At the same time, the high frequencies are sent to the HIGH OUT (9) jack and must then be
patched to the INPUT of the other channel of this amplifier or to another amplifier input to complete
the bi-amped system. With the switch OUT, the crossover is defeated and the input signal is routed
directly to the respective power amp channel. The crossover frequency is fixed at 100 Hz and cannot
be changed. The crossover configuration is a four-pole Linkwitz-Riley approximation.
Efforts should be made to correct the cause of the
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