Crown D-45 Reference Manual page 18

Some applications may require the gain structure to be
calculated based on a sensitivity of 0.775 volts. And
although the 26 dB gain setting provides a sensitivity
for each amplifier that is very near 0.775 volts, the
0.775 volt sensitivity setting is provided for applications
that demand this sensitivity with a high level of preci-
sion.
A Crown Service Center or a technician in the field can
activate the 0.775 volt input sensitivity without voiding
the warranty. To change the input sensitivity, follow the
instructions provided in Appendix A.1.1 for opening the
chassis. Then, use the instructions that follow specifi-
cally for a D-45 or D-75A amplifier. Refer to Figure A.1
for help finding the jumper and resistor locations.
D-45
Desolder and remove the resistors in locations
R103 and R203. In place of the old resistors, solder
¼-watt, 665-ohm (1%) resistors.
D-75A
Solder 22 AWG (0.3255 mm
locations marked R152 and R252 on the main cir-
cuit board.
If you will be operating the unit in dual mode, you can
now reassemble the unit in reverse order of disassem-
bly and reconnect the power. Otherwise, proceed to
configure your amplifier for mono operation.
A.1.3 Dual vs. Bridge-Mono Mode
Your amplifier is configured at the factory for dual op-
eration because it is commonly used in two-channel or
stereo applications. Your amplifier has excellent cross-
talk characteristics, so each channel can be used as
an independent, single-channel amplifier. For common
Page 18
2 ) jumper wires at the
stereo applications, left and right source signals can
be connected to inputs 1 and 2 to drive a pair of stereo
loudspeakers.
For other applications, it may be more desirable to have
higher power output from a single (mono) channel. The
bridge-mono mode makes this convenient.
Bridge-mono mode can be used in single-channel ap-
plications such as paging. It also lets you get the abso-
lute maximum power out of the amplifier, like with the
D-75A which delivers 80 watts (2 x 40) in dual mode
and 110 watts (1 x 110) bridge-mono into 8 ohms. The
bridge-mono mode also provides an easy power and
performance upgrade path for stereo applications. A
single amplifier with adequate power in dual mode
might be used until a second amplifier can be added
for use in a true "dual mono" configuration.
IMPORTANT: Critical differences between dual and
mono wiring are described in Section 2.3.1.
A technician can activate bridge-mono mode without
voiding the warranty. To configure your unit for mono
operation, follow the instructions for opening the chas-
sis in Appendix A.1.1. (The top cover does not need to
be removed.) Then use the instructions that follow. Re-
fer to Figure A.1 for help locating the jumper pins.
1. Remove the jumper from the pins marked with
the words "DUAL" and "MONO."
2. Reinstall the jumper so the two pins closest to
the word "MONO" on the circuit board are
shorted.
3. Reassemble the unit by reversing the steps for
disassembly in Appendix A.1.1.
D-45 / D-75A Power Amplifiers