Orban OPTIMOD-FM 8500S Operating Manual page 294

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TECHNICAL DATA
a floating transformer; its differential output level is independent of whether
one side of its output is floating or grounded. IC301 and its right channel
counterpart IC302 are socketed in through-hole packages to facilitate field re-
placement with simple tools. All other circuitry is surface-mounted.
The corresponding right channel circuitry is functionally identical to that just
described.
Digital Sample Rate Converter (SRC) and Output Transmitter
Located on Input/Output/DSP board
Output sample rate converter (SRC) IC503A converts the 64 kHz 8500S system
sample rate to any of the standard 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, and 96
kHz rates for the 8500S's Digital Out 1. The sample rate converter drives digital
audio interface transmitter IC501B, which encodes digital audio signals using the
AES3 interface format (AES3-1992).
Composite Output Circuit
Located on the Input/Output/DSP board and Composite/SCA daughterboard
A dual composite D/A converter drives the two composite outputs. Using a dual
D/A converter permits the levels of the two composite outputs to be set inde-
pendently in DSP. Each channel of the D/A converter drives a passive LC third-
order anti-imaging filter.
The SCA inputs are summed with the composite output in the analog domain.
The composite output level controls (COMP1 LVL and COMP2 LV) therefore do
not affect the absolute level of the SCA appearing at the 8500S's outputs.
The second SCA input can be jumpered to serve as a pilot reference source for
RDS generators (your 8500S is shipped from the factory in this configuration).
Component-Level Description:
We will describe the signal path for composite 1 output; the signal path for
composite 2 output is exactly analogous. IC401 is a dual-channel high-speed
D/A converter chip that receives the digital composite signal at a 170.66
(512/3) kHz sample rate. Its differential outputs drive current-to-voltage con-
verter amplifier IC403, which drives differential amplifier IC405A. IC405A re-
moves common-mode noise from the D/A output.
IC405B is a DC servo amplifier that removes DC offsets from the D/A output
without introducing significant amounts of low frequency tilt to the compos-
ite waveform.
IC405A drives a third-order passive LC reconstruction filter C9, C10, L9, R17,
R18, on the Composite/SCA daughterboard. (This filter is equalized and phase-
corrected in DSP to obtain excellent flatness and phase-linearity. This opti-
mizes stereo separation.) The resulting signal is a filtered analog representa-
tion of the composite signal generated by the DSP. IC2B buffers this signal
and sums it with the SCA signals from SCA INPUT buffer IC1. Any contribution
from the SCA inputs is therefore not indicated on the
ORBAN MODEL 8500S
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