Advertisement
audience area of a large room will usually result in an
overly bright sound. Common practice is to adjust for
3 dB per octave rolloff of the high frequencies starting
at about 1 kHz. Frequency response is then checked in
other locations in the audience area and, if necessary,
the Equalizer is readjusted slightly to improve the aver-
age response for the entire audience area. Final equaliza-
tion adjustments are based on listening tests using
typical program material.
Equalization of a sound reinforcement system using
instrumentation is similar to playback equalization. The
sound system is equalized initially to produce the desired
house curve with all microphones turned off. The individ-
ual microphone volume controls are then increased to
the approximate use settings, slightly below the feed-
back threshold. The SR107 LEVEL Control is then in-
creased slowly while observing the equalization analyzer.
As the feedback threshold is approached the analyzer
will show a prominent increase in amplitude of the fre-
quency band where feedback is about to occur. The
appropriate SR107 Filter Control setting is then reduced
until the amplitude increase disappears. This process is
continued until the major feedback tendencies have been
suppressed and a reasonable sound volume level is being
produced. A talk or performance test of each open mi-
crophone is then conducted and the quality of the sound
produced is sampled by listening in various locations
throughout the audience area. Additional equalization ad-
justments are made based on the listening evaluation
and taking care to avoid any significant reduction in the
feedback threshold previously achieved.
Equalization of a stage monitor system using analyzer
equipment is similar to playback or house system equal-
ization except measurements and evaluation are confined
to the performer's stage area. The pink noise generator
is connected to the mixer input and the mixer volume
adjusted to provide an output from the monitor speakers
significantly above the ambient noise level. A person is
placed in front of the lead performer's microphone (to
simulate performance conditions) and the analyzer mi-
crophone is placed next to the person at ear level to
sample the sound field in that area. The analyzer micro-
phone output is viewed on the equalization analyzer and
initial response adjustments, such as low frequency roll-
off, are made. The mixer volume control for the per-
former's microphone is then set to a stable point slightly
below the feedback threshold. The SR107 LEVEL Control
is gradually increased until an obvious increase in am-
plitude over a narrow frequency band is noted on the
equalization analyzer. This is the onset of feedback and
the appropriate SR107 Filter Control is used to reduce
the system response in this area. This process is con-
tinued until satisfactory gain before feedback and a
desired response is achieved. A voice test of each per-
former microphone position is made to determine if a
similar feedback threshold is attainable. Final adjustment
of the SR107 and/or individual channel tone controls (if
available) is made to improve quality or intelligibility of
the sound presented to the performers.
Connecting a VU Meter
An external VU meter may be connected to the LlNE
OUTPUT of the SR107 with a series resistor (see Figure
6). Use a true VU meter (such as Simpson 1349) and a
resistor connected as shown. The resistor should be
Yz-watt carbon 5%. With a 600-ohm load zero VU is
$ 4 dBm.
/
TIP WIRE
3 6 0 0 5%
I
I
TO LlNE LEVEL
OUTPUT PHONE JACK
NOTE
I
NO CONNECTION TO SLEEVE REQUIRED.
FIGURE 6.
EXTERNAL VU METER
SERVICE INSTRUCTIONS
Service
The SR107 Audio Equalizer uses components of the
highest quality, operating well within their respective
ratings to assure long life.
W A R N I N G
Voltages in this equipment are hazardous to life.
Refer servicing to qualified service personnel.
Replacement Parts
Parts that are readily available through local electronic
parts distributors are not shown on the accompanying
Parts List. Their values are shown on the Circuit Diagram
(Figure 11). Commercial parts not readily available and
unique parts are shown on the Parts List and may be
ordered directly from the factory.
The commercial alternates shown on the Parts List are
not necessarily equivalents, but are electrically and me-
chanically similar, and may be used in the event that
direct factory replacements are not immediately avail-
able. To maintain the highest possible performance and
reliability, Shure factory replacement parts should be
used. When ordering replacement parts, specify the
Shure Replacement Kit Number, description, product
model number and serial number.
Cover Removal
To service components inside the chassis, the pro-
tective top cover must be removed. This is done by
removing eight screws from the top surface and lifting
the cover off.
Fuse Replacement
The Equalizer is provided with a wired-in main power
fuse F1 which is rated at 1/16A, 250V, Slo-Blo for the
SR107 and 1/8A, 250V, Slo-Blo for the SR107-2E. If re-
placement becomes necessary, replace with identical
fuse. Insulating tubing should be used on the fuse leads
and to cover the metal end caps of the fuse.
Knob Replacement
All front panel rotary control knobs are pull-off types
and are interchangeable.
Ferrite Beads
Ferrite beads are used on the signal leads to all input
and output connectors except the AUX OUTPUT. Be sure
to replace the ferrite beads wherever they have been
removed during servicing.
Printed Circuit Board Removal
The SR107 chassis contains two printed circuit board
assemblies, the Amplifier Board and the Equalizer Board
identified as A1 and A2 in Figure 7. The foil side of board
A1 may be made accessible for servicing by disconnect-
Advertisement
