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Meter Reading
Output
Power
100% 1 X
86.7%
3/4X
70.7% 1 /2X
50
%
1 /4X
33.3% 1/10X
10% 1/1oox
In most applications, the VOLUME Control
(2)
setting
of the Amplifier is determined by the sound level require-
ments of the area
being served. Initial adjustments are
made in the audio console feeding the Amplifier to set the
average program output level to a value convenient for
monitoring on the audio console VU meter, usually
0 VU.
This can be done either with program material or with an
internal tone oscillator as in the Shure
SRlO1 Audio Con-
sole. With this signal as an input to the Amplifier, adjust
the VOLUME Control to provide the desired sound level
from the speakers connected to the Amplifier. At this point,
it is important to note the reading of the OUTPUT VOLTAGE
meter (1). If the average reading is 70% or higher, it is
likely that peak excursions in the program material will
exceed 100% and enter the clipping region of the Amplifier.
If the program material is of relatively constant level, as in
"hard rock" music, this operating condition may be ac-
ceptable or even desirable. It should be noted that a moder-
ate amount of clipping is not readily detectable and is toler-
ated by some users in the interests of maintaining a higher
average sound level at the amplifier output. If the dynamic
range of the program material is expected to be large, as in
a live orchestral or dramatic production, it is advisable to
set the output voltage level to 50% or less to reduce the
possibility of noticeable clipping on loud passages. In
either case, to achieve the best overall performance from
the sound system, the operator should keep in mind the
operating level he has set up for the Amplifier, and control
the console output accordingly.
The tamper-proof cover supplied is designed to replace
the pull-off VOLUME Control knob (2) and keep the VOL-
UME Control at a preset position.
BASIC OPERATING HINTS
Should any difficulty be encountered in Amplifier opera-
tion, the problem may often be traced to some simple
source such as an error in interconnection. The following
is offered as a basic guide to problems of this sort.
Symptom: Amplifier is "dead" (no output, OUTPUT
VOLTAGE Meter lamps out)
Symptom:
Check:
Symptom:
Check:
Symptom:
Check:
Symptom:
Check:
1. Check that ac power source is "live" and
that Amplifier is plugged in.
2. Check that POWER ON-OFF Switch (4) is
on.
3. Check to see that rear-panel
3AG/5A Fuse
(6)
is good.
4.
Check that THERMAL OVERLOAD Lamp
(3) is not lit.
Amplifier is "dead" (no output, OUTPUT VOLT-
AGE Meter lamps lit)
1. Check that VOLUME Control (2) is set high
enough.
2. Check for defective input cable or source.
3. Check for defective output cables or
speakers.
4. Check for input and output cables re-
versed.
No 70-volt output (direct output present)
(SR105A only)
1. Check that 70V-OFF Switch (10) is set to
70V.
2. Check for defective 70-volt output cables
or speakers.
Low or distorted output
1. Check for incorrect speaker load, shorted
or defective cables, and proper connec-
tions.
2. Check that speaker power handling capa-
bility is adequate.
3. Check that 70V-OFF Switch (10) is not
turned on without a 70-volt load
(SR105A;
direct output operation only).
4. Check that output cables are of sufficient
size (gauge) for load.
Hum or noise in output
1. Check for defective source or input cable
by disconnecting input cable.
2. Check need for balanced line on long cable
runs or to avoid ground loop condition be-
tween units.
3. Check speaker line for balance (should not
be grounded at speaker).
4. Check 70V OUTPUT Terminal Strip (11);
grounding the center-tap (CT) terminal may
reduce or eliminate condition
(SR105A
only).
SRl05
Power
Amplifier
SPECIAL OPERATING INSTRUCTIONS
The information contained in this section is provided to
an existing 70-volt system. The Amplifier may be installed
more fully utilize the capabilities of the
SR105 Power
either at the end, or anywhere along the system, by using
Amplifier.
an attenuator such as that shown in Figure 10, Page 11.
Connect the attenuator to the 70-volt line as shown, and
ADDING
SR105A AMPLIFIERS IN A
connect the attenuator plug to the BALANCED BRIDGING
70-VOLT SYSTEM (CASCADED)
Input Jack (5) on the added Amplifier. Set the VOLUME
For added power or when additional speakers are to be
Control (2) on the added Amplifier to
7
to obtain a 70-volt
installed, an additional
SR105A Amplifier may be added to
output when the system voltage is at 70 volts. This will
pro-