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Amplifier Operation
This procedure
applies to mono
systems
(stereo amp
in
bridged mode), as well as to stereo sound systems. It applies
to full-range speaker systems which have a passive high-level
crossover (or none at all). If you are using the amplifiers іп
a multi-amplified
system
with
an electronic
or low-level
passive crossover, the Input
Attenuators
on the amplifier
are generally set to maximum
(zero loss), and all level con-
trolling is done at the crossover (skip step 10).
-—
. Make certain all equipment is OFF.
2. Plug the amplifiers into a grounded 120 Volt, 50—60 Hz
AC power outlet.
3. Connect the wiring from the signa! sources to the ampli-
fier's input (XLR or phone jack).
4. Select
the
appropriate .setting
for the MODE
switch
(MONO or STEREO).
5. Connect
the speakers to the output terminals or phone
jacks. If used in the MONO
mode, DO NOT
USE THE
PHONE JACKS; connect only to the red (4) terminals of
the two channels' 5-way binding posts.
6. Adjust
the
input
Attenuators
to their minimum
level
(infinite loss) setting.
7. Turn on the entire sound system except the amplifiers.
8. Adjust
the controls
on
the signal source
(typically
a
console) for "normal"
indications on the source's meter
or level indicator.
№ there is no metering, then set the
master control at the "nominal" position or mark.
9. Turn the amplifier on. After a short delay, the PROTEC-
TION
indicator should turn off (you may hear a "click"
from within the amplifier as the output relay engages).
10.Gradually
increase the Amplifier Input Attenuators until
the CLIP LED just turns on; given a *4 dBu input signal
and a typical speaker load, this should occur just as the
controls reach the maximum
(zero loss) setting. *
Immediately turn down the Amplifier Input Attenuators
by the number
of dB (per their calibrated scale) that
match the amount
of headroom you wish to preserve in
the sound system. For a high quality music reproduction
system, 20 dB of gain reduction (headroom)
is about the
most normally used. For a live "rock" music performance,
10 to
15 dB
of gain reduction
provides
for a higher
average
level while
retaining
adequate
headroom.
For
paging, or other voice-only or background music systems,
5 to
10 dB
of gain
reduction
(headroom)
should
be
sufficient.
|
*|f the СЫР
LED does not come on with the amplifier
controls at maximum
(zero loss), then the source device
nominal
level is simply lower than —4 dBu. This is not a
problem,
but in order to establish the desired headroom
figure, you will temporarily have to increase the source's
output level. Turn it up until the Amplifier's CLIP LED just
comes
on, and note how much
extra
level you
had to
extract from the source. Now bring the source back to its
nominal
level. Take the number of dB of headroom
you
wish to establish for the system, subtract the "added level"
you
just had to extract
from the source from this total
figure, and turn down the Amplifier Input Attenuators by
the resulting figure.
Precautions regarding AC power source for
amplifiers
High power amplifiers can draw a lot of AC power. Be sure
the AC power source for your AC distribution system has
adequate current capability to bear the entire load with an
extra margin of safety. If you use a power outlet strip with a
built-in fuse or circuit breaker, make sure the breaker is rated
for sufficient current to handle the combined
load of all
equipment plugged into the strip.
E
In multiple amplifier installations, we recommend sequential
turn-on
(either manually
or via timed
relays) to avoid a
sudden, major drain on the AC line.
You should also keep in mind that severe reduction of power
line voltage affects the amount of power you can get FROM
the amplifier. If you need to run long AC extension cords,
make
sure their conductors are as large as practical (small
gauge number). Just as smaller diameter wire causes speaker
line loss, smaller power lines cause loss. However, the effect
of small AC lines is one of intermittent clipping under severe
low-voltage conditions.
WARNING
DO
NOT
CHANGE
A
THE
FUSE
OR
CIRCUIT
BREAKER
IN
THE
AC
POWER
DISTRIBUTION
SYSTEM
TO A HIGHER
VALUE UNLESS
YOU ARE
ABSOLUTELY
CERTAIN
THE
WIRING
IS RATED
FOR
THE HIGHER
CURRENT.
If a high-current short
occurs,
the wiring becomes
the "fuse," which usually
starts a fire before the wiring can "blow".
We recom-
mend
that you refer to the National
Electrical Code
before attempting any such change.
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