Orban OPTIMOD-FM 5500 Operation Manual page 231

OPTIMOD-FM DIGITAL
right analog output connectors. These analog signals can represent either the
transmitter or monitor output of audio processing.
Component-Level Description:
IC303 and associated components filter the left channel signal emerging from
IC306. The purpose of these stages is to reduce the out-of-band noise energy
resulting from the delta-sigma D/A's noise-shaping filter and to translate the
differential output of the D/A converter into single-ended form. These com-
ponents apply a 3
This filter does not induce significant overshoot of the processed audio, which
would otherwise waste modulation.
IC305B and associated components form a low-frequency servo amplifier to
remove residual DC from the signal. The 0.1Hz
induced overshoot in the processed audio.
The buffered output of IC303B is passed through gain trimmer VR301, which
allows the gain of the output circuitry to be calibrated to a standard. IC301, a
balanced output line driver, receives the output of VR301. This driver emulates
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.
3. Digital Sample Rate Converter (SRC) and Output Transmitter
Located on Input/Output/DSP board
Output sample rate converter (SRC) IC503A converts the 64 kHz 5500 system sam-
ple rate to any of the standard 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, and 96 kHz
rates for the 5500'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).
4. 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 5500's outputs.
The second SCA input can be jumpered to serve as a pilot reference source for
RDS generators (your 5500 is shipped from the factory in this configuration).
rd
order low-pass filter to the differential signal from the D/A.

3 dB frequency prevents tilt-
6-11
TECHNICAL DATA