dbx 3BX III, Руководство по обслуживанию

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Model 3BX III Service Manual
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Finally, the output of the impact-disable circuit connects to the summer
stage (2/2-U719) previously mentioned, where both the expansion and
impact-restoration CVs are combined before being sent to the VCA. Trim
pots (VR721 and VR722) are provided at the output of this summer to allow
the CVs sent to each VCA (left and right channel) to be offset slightly,
in order to account for differences in VCA-gain offsets (see Alignment
Procedure, section 6, p.13).
Low-Band CV Path
This path is nearly identical to the high-band, except that the time-
constants used throughout are generally much longer, as is appropriate
for low frequencies. The signal at TP10 (the output of the buffer
following the low-band rms output) splits into two paths: one to the
expansion control (VR711) and one to the impact detector. The output of
the impact detector goes through a circuit to lengthen the decay, and
then to the impact-disable circuit. (The impact-disable controller is
common to all three bands.) The impact-control signal and the expansion-
control signals are combined in 1/2-U718 and then sent to the low-band
VCAs. Trim pots VR717 and VR718 are provided to set the VCA gains
precisely.
Mid-Band CV Path
This path also closely resembles the high-band, except for different
time-constants (midway between the low- and high-band ones) and the
addition of a mid-band expansion time-constant circuit. This circuit is
placed between the output of the buffer following the mid-band rms
detector (TP12) and the front panel expansion control (VR713). Its
purpose is to prevent the mid-band CV from dropping too fast after an
input signal goes away (toward lower signal level indication, which at
this point is toward positive voltages). This circuit closely resembles
the impact time-constant circuit; it performs a similar function but does
not provide a user-adjustable release rate.
LED DISPLAYS
Refer to Fig. 5, a block diagram of
a typical LED display. The control
voltages from each of the three
sections of the Impact-Restoration
control are summed in 1/2-U719 to
produce a signal representative of
the average of the impact CVs.
This signal is sent to the LED-
display section. In addition, the
CVs from each of the three sections
of the Expansion-Level control
(VR711, VR713, and VR715) are sent
(separately) there.
Figure 5, LED Display
(see Fig. 4)
(again see Fig. 4)