Controls - Crown D-75 Service Manual

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Appendix B: Operation
B.1 Precautions
Allhough your amplifier is well proteCted from any external
faults, we recommend the following precautions be taken ior
safe operation:
1. When using input sources of uncenain level or 2.-1y
audio components which have
not
previously been
used with your amplifier. always begin wilh the level
controls at a minimum and gradually increase them
while monitoring
the
audio output level to I!void
suddenly blasting !he loudspeakers.
2. Always tum lhe level conltOls down before insc.,"ting a
headphone sct into me output monitor jack on the
front panel. This will eliminate the risk of damaging
the headset or your cars
willi
high sound levels.
3. Tum the ampiifier off and unplug
j!
from the AC line
before replacing lhe fuse. (The unil must be totally
disccnn~led
[;om Ii'll.! AC power source because tile
fuse socket is slill powered even when the unit is
turned off.)
4. Operate Ihe amp with the correct fuse (2 amp for 100
or 120 VAC; 1 amp for 200, 220 or 240 VAC).
5. Never drive a traflsformer-couplcd device (such as an
electrostatic loudspeaker) or any other device whicb
appears as a low-frequency short (less than 3 ohms)
without a series isolating capacitor. Such
~...ration
may damage tbe load and/or needlessly activate the
amplifier's VI limiting.
6.
Operate
lhe amplifier from AC mains of not more than
10% above lhe selected line voltage and
only!h~
specified line frequency (50/60
Hz).
F~ilu.e
10
comply with these limits will invalidate the warranty.
7. Never connect the output to a power supply output,
battery, or power main. Damage incurred by sucb a
hookup is not covered by me warranty.
8. Do not expose the amplifier to corrosive chemicals
such as soft drinks, lye, sall water, ete.
9.
Do
nOi tamper with lhecircuiuy. Circuit changes
made by unauthorized personnel, or unauthorized
circuit modifications, will invalidate the warranty.
B.2 Controls
Independent level controls and a power switch and power
indicator are located on the front panel. Bom level controls
are used in STEREO mode, but only theChanncll control
should be used in MONO mode. They areused
to
adjuSt the
desired output level (both the monilOr output and
t.h~
main
outputs) and have thirty one detents for precise adjustment.
The openttion mode is switched between SlEREO and
MONO by the Stereo-Mono switch located on the back
panel. Also located on the back panel is an AC line fuse.
In addition
to
the above essential conrrols, your high-
performance amplifier has an IOC (Input/Output
Compa.rilOr) indicator and a Signal ?resence indicalOr for
each channel.
The red iOC LEOs are located on the from panel above the
level comrois. They will flash or glow whenever the
distortion speciflC2.tions of the amplifier are being exceeded.
Note: The ICC indicators also double as STAND-BY
indicators and wiil glow every time this feature is active
(tum-on delay, Low-Frequency Imerrupt and temperature
overload). It is also normal for them to glow momentarily
when the AC power
is turned off.
Tne ;;reen Signal Przscnce LEDs are located on the from
pane.:.
retweeo
the level controls.
They blink or glow any
time !.b.e:-e is more
!.h2.n 0.6 V RMS at the outDUlof the Q-7.'i.
(Ii JoesignaJ level is very low they may notilluminatc.) This
provides a eonvcnientmethod of observing whemer
or
nOt a
signal has been interrupted somewhere in bet ..... een tbe input
and tile
OUtpUL
B.3 Protection
Crown p::lwcr amplifiers
are
widely kno ..... n for their quality
construction, high reliability and extensive internal
protection circuitry. The D-75 is no e"ception. It is
prot.ected against all the common hazards which plague
high-powered amplifiers, inclueling:
shorted,
open and
mismatched loads (load impedance
100
low): overloaded
power supplies: er.cessive temperature; chain destruction
phenomena; inpm overload damage; and, high frequency
overiood blowups.
PrOl.ection against shoned and low impedance loads is
provided by a fast -acting limiter circui t wh ich
instanUlllcously limits the output power to a maximum safe
stress value.
It
functions automatically as a current limiter
at audio frequencies whose current limiting threshold is
depcndenl on the history of theoutput signal. Output current
causes the threshold
to
increase. The no-signal threshold is
high enough LO allow lOne bursting (even into 4 ohms)
without premature limiting, as is found in some recent
products or other manufacturers.
Since !.he Iimiler h2.S no instantaneous response to output
voltage. Oyback transients do not appear in the outpul when
limiting occurs on inductive loads. (Flyback transients are
a normal by-product of VI limiting, also called "Energy
Limiter," with an inductive load.
The
amplifier yields to the
Appendix
8 8-1