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O PERATION
POWER SWITCH
The POWER switch is located on the front panel of the amplifier. An internal lamp indicates when it is turned
on. Standard practice is to turn the amplifier on last and off first when switching components individually to
prevent sending damaging transients, generated in the source components, to the speakers. It is possible to
leave the power switch in the on position and switch the amplifier remotely through a power distribution
block or preamp switched outlet. When doing so make sure the switch is rated for the current required by the
amplifier.
LEVEL CONTROLS
The input sensitivity, for each channel, can be adjusted individually using the level controls on the front panel.
The gain control on an amplifier is usually fully advanced to its maximum (rated) sensitivity. In public systems
where it is necessary to match levels, the knobs can be removed and the controls adjusted with your fingers
or a flathead screwdriver. Cover the holes with the enclosed plugs to restrict access.
INPUT CONFIGURATION SWITCHES
Stereo/Bi-Amp
The rear panel STEREO/BI-AMP switch controls the signal routing in the amplifier. In the STEREO
position, the signal is supplied independently to Channel 1 and Channel 2. In the BI-AMP position,
the signal is fed to both amplifier channels from the Channel 1 input, while retaining full use of the
level controls and XCard crossovers. This allows the amplifier to be used in dual-mono or bi-amp
systems without requiring auxiliary equipment.
Normal/Bridged
The amplifier operates in two-channel mode when the front panel NORMAL/BRIDGED switch is in
the NORMAL position and the rear channel switch is set for STEREO. To use the amplifier in single
channel, bridged mono applications, the front panel switch must be in the BRIDGED position. When
the switch is set in the BRIDGED position, the Channel 1 (+) and (–) inputs are connected to Channel
2 in reversed polarity, which inverts the Channel 2 output. Only the Channel 1 input is used, and the
speaker is connected to the two RED binding posts. The amplifier gain is adjusted by the Channel 1
level control; the Channel 2 control is not active. Because of thermal considerations we do not
recommend using less than a nominal eight ohm load on the amplifier when running it in mono.
XCARD CROSSOVERS
The XCard modules contain the resistors and capacitors which control the frequency at which the card
operates. The orientation of the card in the socket determines the operating mode of the crossover. The XCard
is labeled to indicate the function of each face. The full range face is marked with a double arrow to show that
both edges operate full range. The other face operates as either high-pass or low-pass and an arrow is printed
by the function to indicate which edge to insert into the socket.
Each amplifier channel uses two XCards. When both cards are set full range, the full frequency response of
the amplifier is used. When one card is set full range and the other for either high-pass or low-pass, the signal
is crossed over at 12dB per octave with a Butterworth alignment at the frequency determined by the card which
is used. When both cards are set for the same operation, whether it is high-pass or low-pass, the signal is crossed
over at a 24dB per octave slope. When one card is set for low-pass and the other for high-pass, a bandpass
crossover limits the signal to the frequency range determined by the cards which are used. The slope of the
filter is 12dB per octave. There is no effect on the bandpass operation regardless of which of the cards is used
for the high-pass or low-pass function.
Assembled XCards are available at a variety of operating frequencies. Since there will be situations which the
stock cards will not satisfy, instructions for building XCards for specific applications have been included in
the Technical Reference section of this manual.