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Operating
Operating Controls
Front Panel
+35
+30
+25
+20
+15
Gain Control
Use the Gain control to adjust the output level of the 786. Note that the Gain control is used as a
"coarse" adjustment, ranging from +15dB to +65dB of gain, in 5dB increments. The Gain control is not
a "pot", or in other words, the signal does not go through this control. The Gain control is a relay-based
system which "tells" the 786 how much gain should be applied to the signal. You should always set the
Gain control to one of the detents. Do not set the Gain control between detents.
Fine Control
The Fine control further adjusts the gain in a sweepable fashion between -5dB and +5dB. If you set the
Gain control to +45dB of coarse gain and the Fine control to -3dB of fine gain, your overall gain will
be +42dB.
Spectrum Control
Use this control to set the frequency where the EQ section boosts or cuts 3dB. The range of this control
is 5kHz to 40kHz. Obviously there is no fundamental frequency material at the 40kHz frequency, how-
ever, due to the slope of the EQ curve, frequencies in the audio range are affected. Also, boosting at this
frequency emphasizes harmonic information that is sometimes referred to as "air" or "space" in the sig-
nal. This control is calibrated to the frequency at which 3dB of boost or cut occurs when the Detail con-
trol is set at +16dB or -16dB respectively.
Detail Control
This control adjusts the amount of boost or cut of the high frequency shelving EQ. The range is -∞ to
+16dB. "-∞" is typically better than -30dB. The cut and boost curves are symmetrical from 16dB boost
to 16dB cut (ie: a 2dB boost produces a shelving curve that is the mirror image of the shelving curve
produced by a 2dB cut). When the control is set to -∞, the band acts like a low pass filter whose slope
is determined by the 12dB/OCT switch.
12dB/OCT Switch and LED
Engage this switch (the adjacent LED will light) to set the slope of the shelving curve to 12dB/Octave.
Leaving the switch in the "out" position sets the slope to a gentler 6dB/Octave rate. For example, a 12dB
setting for the slope can let you create a sense of "air" without the stridency caused by too much boost-
ing of upper mid range frequencies. Figure 4 on the next page shows the behavior of the 786's EQ sec-
tion.
HF EQ switch
The hardwired EQ in/out switch bypasses the EQ circuit in the audio path. Settings on the Detail and
Spectrum controls, as well as the 12dB/Octave switch are nullified by disengaging the HF EQ switch.
6
controls
786
+40
+45
7 5 3
20 10
+50
-
-20
-15
-25
-30
DECIBELS
+55
+60
+65
0
3
+30
+
-10
-5
0
+25
¨
+20
+40
+35
+45
20 10
+50
-
-30
+55
+60
+15
+65
7 5 3
0
3
+
-20
-15
-10
-25
-5
0
DECIBELS
¨
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