Inovonics 235, Инструкция по эксплуатации и техническому обслуживанию

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Section IV
CIRCUIT DESCRIPTIONS
This section details circuitry of the Inovonics Model 235 AM Broadcast
Audio Processor. Circuit descriptions refer to four pages of Schematic
Diagrams contained in the Appendix, Section V, Pages 29 through 32.
If you’re looking for some sort of alignment procedure for the 235,
forget it. There are no internal controls for any sort of calibration, the
circuitry being rock-solid through impeccable design.
NAVIGATION
Schematic component reference designations have not been assigned in
as haphazard a manner as they might at first appear. Instead of
annotating the schematic in a logical sequence, we instead chose to
designate the components on the circuit board following their physical
placement, top-to-bottom, left-to-right. We expect this practice will
prove useful when troubleshooting, making it easier to locate the
physical part after analyzing the diagram.
The Model 235 schematic consists of three sheets which cover the main
circuit board and the front-panel assembly. Main-board components
begin with the number “1”; i.e.: R1, C1, IC1. Front-panel components
are in the five-hundred series; i.e.: R501, S501.
The front-panel assembly interconnects with the main board using
three short ribbon-cable jumpers. J2 on the main board mates with
J502 on the panel assembly, J4 to J504, and J5 to J505.
INPUT STAGE (Schematic Sheet 1, Page 29)
Line Input
Balancing
IC36B is an “active-balancing” stage for the program line input,
affording good RF suppression and rejection of other, unwanted
common-mode signals. When R183 is jumpered into the input network
with JMP1, the Line Input accepts “High” program levels between
0dBu and +15dBu. For “Low” level inputs, between –15dBu and
0dBu, R183 is jumpered out of the circuit. Input range jumpering is
described on Page 9.
High-Pass
Subsonic Filter
IC37B performs the dual function of a variable-gain stage and a 50Hz
high-pass filter. Assuming negligible musical content below 50Hz, we
can maximize loudness and optimize transmitter modulation by
attenuating program frequencies below 50Hz at a rate of 12dB-per-
octave. Referring to Figure 2 on Page 5, the direct effect of this rolloff
can be seen in the curve for 0dB, “flat” low-frequency equalization. Its