Bass Equalizer - Orban 8100A/XT2 Operating Manual

Technical Information
6-5
scheme is that the summed outputs of the four clippers can be applied to a safety clipper
for final peak limiting without the need for further broadband gain control, thereby avoiding
potential pumping and modulation effects. In the 8100A/1 + XT2 System, the 8100A/l ' s
FCS Overshoot Compensator serves as a " band-limited safety clipper " to effectively control
peak modulation without introducing out-of-band energy which could cause losses of dynamic
separation and increases in main-to-sub crosstalk. (This design is protected by US Patents
#4,208,548 and #4,412,100.)
For more information about 8100A/1 circuitry, see the 8100A/1 Operating Manual.
2) HIGH-FREQUENCY FILTER AND MAIN CLIPPER DEFEAT
The signal is pre-emphasized by the 8100A/1, then sent to the XT2 from the output of the
8100A/l ' s high-frequency limiter. Whenever the XT2 is plugged into the 8100A/1, this HF
limiter is forced into PROOF mode by a jumper (within the XT2) that completes a connection
between the 8100A/l ' s +15V power supply and its limiter proof bus; this also defeats the
main clippers on Cards #8 and #9. The ±4.2V supply on the 8100A/l ' s Card #6 (which
activates the the 8100A/l ' s FCS Overshoot Compensator and safety clipper) is isolated
from this jumper by means of a diode, and remains operational unless the 8100A/l ' s LIMITER
switch is set to PROOF.
Component-level description:
Further information about the HF limiter and
main clipper can be found in the Operating
Manual for OPTIMOD-FM.
3) BASS EQUALIZER
Card #A1
The input signal to the XT2 is first applied to a bass equalizer. This produces a peaking
boost (i.e., bell-shaped curve) with a center frequency of 65Hz, a " Q " of 1.4, and a boost
variable from 0 to +10dB.
Boost is produced by subtracting the output of an inverting second-order band-pass filter from
the main signal (resulting in an overall addition).
Component-level description:
A bell-shaped bass boost is achieved by subtract ­
ing (in IC19b) the output of inverting band-pass
filter IC19a and associated components from the
filter ' s input. (Note that IC19b is inverting for
the main signal and non-inveriing for the output
of IC19a.)
For a discussion of the inverting band-pass fil ­
ter, see (for example) Chapter 6 in Wong and
Ott ' s Function Circuits (McGraw-Hill, New York,
1976).
If the equalizer fails, first check IC19. If this fails
to correct the problem, the passive components
R70, R71, R73, C23, C24 must then be checked
out on an impedance bridge.