Ch4 And Cl4; Audio Signal Path - Crown CH Series Operation Manual

CH and CL Series Power Amplifiers
5 Principles of Operation
Operation Manual

5.2 CH4 and CL4

5.2.1 Audio Signal Path

For the sake of simplicity, only channel one of
the audio signal path is described.
Signal is presented to the CH4/CL4 through
one of three connectors when using the stan-
dard input module. Each channel is outfitted
with a balanced XLR/phone jack, and a barrier
strip. These connectors are wired in parallel,
which allows daisy chaining when needed. The
signal is then converted from balanced to
unbalanced in the Balanced Input Stage where
it also receives RFI protection. Signal then
flows into the Variable Gain Stage where the
front panel level controls are allowed to affect
the gain.
Following this stage, the signal goes through a
gain stage that allows for the various positions
of the sensitivity settings. The signal is then put
under the control of a full-time compressor cir-
cuit comprised of a symmetrical window detec-
tor, a buffer amplifier, and the gating op amp
which uses several small components to set the
compressor's attack and decay characteristics.
The actual compressing is accomplished by an
opto-isolator that affects the gain in the signal
path.
Next, the signal enters a 32-kHz 7th-Order
Gaussian Low-Pass Filter. This filter prevents
the modulator stage and the output filter (both
described below) from receiving signals that
are too high. Without the 32-kHz filter, the
modulator would be unable to process signals
that are too high and the output filter would not
Figure 5.3 Model CH4 Circuit Block Diagram
yield the proper frequency response behavior.
The Gaussian filter type is unique in that it has
minimal ringing and excellent phase response
so even a high-order filter such as this one
does not adversely affect the sonic excellence
of the product.
In the CH4, the signal then travels either
through the HP filter module or is bypassed
around it depending on the position of the
channel operation switch. With the switch set in
the 70V position, the filter is enabled. The filter
is an 18 dB-per-octave high-pass with a –3-dB
rolloff at 70 Hz. This provides a measure of
protection to step-down transformers used in
distributed speakers installations. With the
switch set in the 4/8-Ohm setting, the filter is
bypassed. The power is delivered to the load
cables through the output connector panel
which consists of one of several options.
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