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formance, be sure to check operation in all
back has been eliminated as outlined above, ac-
microphone positions.
tuate each switch and note the tonal character of
1.
Connect line cord to ac power source or use
A67B Battery Power Supply.
Set panel controls as follows:
ON-OFF Slide Switch to ON position.
Mode Slide Switch to BYPASS position.
BELOW
63
and ABOVE 8K Slide Switches to flat
(up) position.
All eight FILTER FREQUENCY Controls to full up
position.
FILTER LEVEL Control to Zero (fully counter-
clockwise).
2.
Adjust the amplifier gain of the sound system
(using the mixerlpreamplifier or power amplifier
volume control) until feedback becomes apparent.
Reduce the gain setting until it is comfortably
below the feedback level.
3.
Set MODE Slide Switch to FILTER position. In-
crease FILTER LEVEL Control until feedback
squeal or ringing is heard.
4. If the feedback sound is high pitched, one of the
four high-frequency FILTER FREQUENCY Controls
(1K through 8K) will be most effective in elimi-
nating the feedback. Individually move each FIL-
TER FREQUENCY Control slowly from top down-
ward and back to top while listening to the feed-
back. The control which eliminates feedback with
the least motion should then be moved down only
so far as necessary to eliminate the feedback.
5.
If the feedback frequency happens to fall between
the bands covered by two adjacent controls, then
it may be necessary to move both controls down
to obtain the desired feedback suppression.
6. If the feedback sound first noted in step
4
is of a
low frequency, then the adjustment procedure
should be started using the low-frequency (63
through
500)
FILTER FREQUENCY Controls.
7.
Having eliminated the first feedback condition,
increase the gain of the sound system with the
FILTER LEVEL Control until feedback is again
noted. Repeat the procedures of the preceding
steps
3
through
6
to eliminate the new feedback
condition. This may require adjustment of a dif-
ferent FILTER FREQUENCY Control or may re-
quire a further decrease in the control or controls
previously moved down.
8. Repeat step 7 until either (a), one or two FILTER
FREQUENCY Controls has been set to maximum
attenuation, or (b), feedback appears to occur at
more than one frequency simultaneously. Do not
reduce the setting of any FILTER FREQUENCY
Controls more than necessary to stop ringing or
squealing during the above procedure.
9. Conduct a talk test through the sound system
with the MODE Switch set to FILTER and listen
for ringing. If ringing is noted, attempt to eliminate
it by a slight decrease in the setting of the FILTER
LEVEL Control or further decrease in the appro-
priate FILTER FREQUENCY Control setting.
10.
During the above procedure, it will not usually be
necessary to set either the BELOW
63
or ABOVE
8K Switches to the down position to eliminate
feedback unless the pitch of the feedback is ex-
tremely low or extremely high. These switches
are primarily intended for improving overall sound
quality or tonal balance, if necessary. After feed-
the system during the talk test. It will usually be
advantageous to actuate the BELOW
63
Switch
if the
63
FILTER FREQUENCY Control is set below
6,
and to actuate the ABOVE 8K Switch if the 8K
FILTER FREQUENCY Control is set below
6.
11. Conduct a talk test and compare the system
sound quality with the MODE Switch in each posi-
tion. The FILTER mode should have improved
quality over the BYPASS mode. If it does not,
reduce the amount of equalization by moving the
FILTER FREQUENCY controls up and decreasing
the FILTER LEVEL Control setting. Note that ex-
cessive equalization can produce sound inferior to
that of the original, unequalized sound.
SPECIFICATIONS
Voltage Gain (Frequency
1000
Hz, no filters activated):
Bypass Mode:
Input
Output
Lo-Imp. Mlc.
Hi-Imp. Mic.
To Pwr. Amp. To Guitar Amp.
Microphone
-23.0
dB
+
1.5 dB
+
24.0 dB
+
7.5 dB
lnstrument
4 1 . 0 dB
-16.5
dB
+
6.0 dB
-10.5
dB
AUX.
4 7 . 0 dB
-22.5
dB
0 dB
-16.5
dB
Filter Mode (FILTER LEVEL Control full clockwise):
Input
Output
Lo-Imp. Mic.
Hi-Imp. Mic.
To Pwr. Amp. To Guitar Amp.
Microphone
+
2.0 dB
+26.5 dB
f 4 9 . 0 dB
+32.5 dB
lnstrument
-16.0
dB
+
8.5 dB
+31.0 dB
+14.5 dB
AUX.
-22.0
dB
+
2.5 dB
+25.0 dB
+
8.5 d B
Frequency Response (BYPASS mode or FILTER Mode,
no filters activated):
Flat
i 2
dB,
40
Hz to
20
kHz.
Hum and Noise, Maximum:
Equivalent lnput Hum and Noise, High-Impedance Mic.,
33
kilohm Source,
20-20
kHz:
100
dB below 1 volt.
Equivalent lnput Noise, High lmpedance Mic.,
33
kil-
ohm Source,
300-20
kHz:
103
dB below
l
volt.
POWER AMPLIFIER OUTPUT Hum and Noise,
20-20
kHz:
7 1
dB below
1
volt.
POWER AMPLIFIER OUTPUT Noise,
300-20
kHz:
73
below
1
volt.
Output Clipping Levels, Minimum:
MIC OUTPUT (LO):
22
mV
MIC OUTPUT (HI):
330
mV
OUTPUT TO POWER AMPLIFIER:
5
volts.
OUTPUT TO GUITAR AMPLIFIER:
750
mV.
lnput Clipping Levels, Minimum:
MICROPHONE INPUT:
450
mV
INSTRUMENT INPUT:
3.6
volts
AUX INPUT:
5
volts
Total Harmonic Distortion:
0.5%
maximum THD at 1 kHz, at POWER AMPLIFIER
OUTPUT level of
1
volt in BYPASS or FILTER mode
with FILTER LEVEL Control full up.
Impedances:
Input
Designed for Use With
Actual
Microphone
High Impedance microphones or
200
kilohms 3520%
lnstrument
{'
~nstruments
j
115
kilohms +20%
Aux
High Level Sources
50
kilohms
f
20%
Output
Deslgned for Use With
Actual
Lo-Imp. Mic.
25 to 600 ohm microphone circuits
60 ohms
+20%
Hi-Imp. Mic.
High impedance microphone circuits
5.0 kilohms +20%
To Power Amplifier Hlgh ~mpedance
-
10 kilohms or
1.0 kilohms +20%
To Guitar Amplifier {greater-unbalanced
aux circuits]
8.2 kilohms *20%
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