Specifications

Controls Connectors lndicators
Peak lndicators Equalizers FEEDBACK FINDER'"
I Dl3 PCAH lndicators
Are connected to power amplifier outputs and
indicate peak output level.
0 DB PEAK equals
approximately 25 watts to a 4-ohm load. A 6 dB
change is a 4-times power change; therefore,
-36 dB represents a 6
mW output and +6 dB a
lOOW output. These indicators are also used to
provide an instantaneous readout of feedback
frequency (see FEEDBACK FINDER). (Note that
when the FEEDBACK FINDER isactivated, the
DB PEAK indicators for that channel are
converted to frequency band indicators and do
not indicate the signal level.)
I PA (Power Amplifier)
Overload Indicators
Light when the power amplifiers exceed approximately 1% d~stortion
level (caused by clipping, overload, or any condition resulting in
imperfect signal amplification). The indicator is sensitive to line
voltage and speaker load conditions. The overload condition can
generally be corrected by turning down the MASTER volume control.
If the indicator remains on, the speaker load may be improper or a
speaker cable may be shorted. It may remain on during SHUTDOWN
activation. Under normal conditions, this Indicator corresponds to a
level of
+9 dB on the DB PEAK indicator or 200watts to a4-ohm load.
I Graphic Equdizers
Are two 10-band, fully combining, minimum-phase, octave type,
normally connected to the power amplifier inputs. They provide13 dB
boost or cut at 63,125,250,500 Hz,
1,2,4,8, and 16 kHz, plus
BELOW 63 Hz 12
dB/octave cutoff filters. The graphic equalizers pern
adjustment of the sound system frequency response for a tonal
balance appropriate to the performance and a reduction in the
tendency toward feedback. They can also be used to adjust an audio
playback system frequency response to compensate for variations in
electrical and
acoust~cal response that can alter the natural sound of
the recorded material.
The graphic equalizers can also be used to produce
dlsco-type
sound by moderate amounts of low- and high-frequency boost.
Note that equalization by ear for proper sound quality requires a
certain amount of
skill and time. It is preferable to use a commercially
available equalization analysis system such as the Shure
M615AS
Equalization Analyzer System, followed by feedback tuning using the
built-in FEEDBACK FINDER and indicators (see next section).
IMPORTANT: Don't overequalize! Too much
equal~zatlon can result In
unnatural and quite unpleasing sound.
No indicator is provided for either the 63 Hzfilter control or BELOW 63
Hz filter switch; any low-frequency problems likely to be encountered
can
beeasily removed by adjustment and listening tests. Reduce the
63 Hz equalizer or move the switch to BELOW 63
(T) if the sound is
boomy" or if extremely low-frequency noises such as "pop" or wind
noise are causing power amplifier overload.
Since the graphic equalizer controls may overemphasize or remove
desirable program
material, you should minimize acoust~c problems
(including feedback) by careful microphone and speaker placement
before equalizing.
The FEEDBACK FINDER uses the LED indicators to provide a quick and easy means of determining the
frequency (octave band location) of the most prominent feedback tones. The graphic equalizers can
then be used to reduce the system response at these frequencies to sup ress feedback. Connect all
speakers and microphones and place them in their proper positions for
tEe performance. Set master
controls and individual input channel MONITOR,
EFFECTSIREVERB and EQ controls to 0. Set all other
individual input channel controls to the initial
(oran e mark) positions. Set the FEEDBACK FINDER
switch to the desired output channel (A or B). The
83 PEAK indicators for the channel selected are now
connected for the feedback indicator function. Adjust the MASTER volume for that channel to just below
feedback. If necessary, turn down the FEEDBACK FINDER THRESHOLD control from the 10 position to
the point where room background noise does not light any DB PEAK
indicators. Increase the MASTER
volume until feedback just occurs and note the highest frequency band with a lit LED. Reduce the
equalizer setting in this band until feedback stops. Repeat the last two steps until the feedback sound
becomes a combination of a number of tones, or until one equalizer control has been set to -10.
IMPORTANT Don't overadjust the equalizer! Too much equalization can result in unnatural sound. With
practice, the FEEDBACK FINDER can be used toequalize for feedback without subjecting the audience
to ear-splitting feedback levels.
If operation is in the stereo mode, repeat the above procedure for the second channel, with the first
channel turned off. When completed, perform a listening test using program material similar to the
planned performance and, if necessary, make slight adjustments to the equalizers to provide the most
pleasing sound.
When using one of the graphic equalizers for stage monitor speakers, feedback suppression of the
monitor system is performed after the house system
and with the main speakers off. The monitor
speakers must be in their final operating positions relative to the microphones used. Use the same
procedure as for the house system except use the individual MONITOR level and MONITOR MASTER
controls for level adjustments. If more than one performer's microphone is involved, select the lead
performer or center stage microphone for operation in the feedback suppression procedure. NOTE:
During this procedure a person must stand in front of or hold (simulating a performer) the microphone
being equalized. Since excessive low-frequency signals are not usually desirable for stage monitors, it
may be advisable to set the equalizer
FLATIBELOW 63 switch of the monitor channel to BELOW 63, the
63 Hz control to -10, and the 125 Hz control to -5. Adjust the FEEDBACK FINDER THRESHOLD,
MONITOR MASTER and
EQualizer controls using the procedure previously described. Conduct avoice
test and check for adequate level and intelligibility. Make a similar check of all other microphones being
fed to the monitor system. Intelligibility may be improved if desired by a slight increase of equalizer
controls in the 1 kHz to
4 kHz range, providing the desired level can be maintained without feedback. If
feedback or ringing is encountered at any microphone location, try adjusting the position of
and/or the
distance to the nearest speaker.