Page 10
D-45 / D-75A Power Amplifiers
The amplifier is switched between dual and bridge-
mono operation with the dual/mono jumper located in-
side the amplifier (see Appendix A).
The unit’s input gain is 26 dB as determined by 1%
precision resistors in the feedback loop. This can be
changed to a sensitivity of 0.775 volts by following the
instructions provided in Appendix A.
3.4 Protection
Your amplifier is protected against all common hazards
that plague high-power amplifiers, including shorted,
open or mismatched loads; overloaded power sup-
plies, chain destruction phenomena, input overload
and high-frequency blowups.
Protection against shorted and mismatched loads is
provided by an instantaneous limiter that automatically
limits current to the maximum safe value for the output
transistors. With a loudspeaker, you can tell the ampli-
fier has activated load protection because it causes
audible distortion. The noise might be compared to
crossover notch distortion or a snapping sound, de-
pending on the load characteristics. Loudspeaker sys-
tems with impedances of 4 ohms or higher should not
activate the protection system.
All voltage amplification circuitry is designed to limit
current. So in the extremely unlikely event of a device
failure, the amplifier will prevent further damage. The
input stages are protected from overload damage by
series resistors. The unit also features a controlled slew
rate and a V-I limiter that protect the amplifier from high-
frequency (RF) blowups.
3.5 Fuse Replacement
The AC mains fuse is located on the back panel be-
side the power cord. This fuse will not blow unless
something is wrong. Before replacing the unit’s fuse,
you should be sure to fix the source of the problem. If
the problem is not immediately apparent, the unit prob-
ably needs to be serviced by a qualified technician.
WARNING: Always unplug the amplifier from the AC
mains before removing the fuse.
To replace the fuse, turn off the power switch and dis-
connect the power plug from the AC mains. Unscrew
the fuse holder cap and remove the fuse. For 100 or
120 VAC operation, replace the fuse with a 2 amp type
3AG fuse; and for 200, 220 or 240 VAC operation, use
a 1 amp type 3AG fuse. Then, simply resecure the fuse
holder cap and reconnect the AC mains.
IMPORTANT: Never install a fuse that has a higher
current rating than the recommended value.
