Optimod-Surround 8685 V1.0 Operating Manual - Orban

6-10
TECHNICAL DATA ORBAN MODEL 8685
Output Circuits
This circuitry interfaces the DSP to the analog and digital audio outputs. The digital
audio from the DSP is transmitted to the digital-to-analog converter (D/A) and output
sample rate converters (SRC). The digital-to-analog (D/A) converter converts the
digital audio words generated by the DSP to analog audio. The analog output
stages scale and buffer the D/A output signal to drive the analog output XLR connectors
with a low impedance balanced output. The digital output transmitter accepts
the digital audio words from the output sample rate converter (SRC) and
transmits them as AES3id-format digital audio signals on the digital output connector.
1. Stereo Digital-to-Analog (D/A) Converter
Located on Input/output board
The D/A, IC200, is a stereo, 24-bit delta-sigma converter. It receives the serial left
and right audio data samples from the DSP at 48 kHz sample rate and converts
them into audio signals requiring further, relatively undemanding analog filtering.
IC211 is surface-mounted and is not field-replaceable without surface-mount
rework equipment.
SDI Option:
The circuitry of the D/A converter and analog output stages is the same as for SDI
and the base configurations, but the reference designators are different. To understand
this circuitry on the SDI module, compare the schematics on pages 6-82
and 6-55.
2. Analog Output Stages
Located on Input/output board
The left and right analog signals emerging from IC200 are each filtered, amplified,
and applied to a floating-balanced integrated line driver, which has a 50Ω
output impedance. The line driver outputs are applied to the RF-filtered left and
right analog output connectors. These analog signals can represent either the
transmitter or monitor output of audio processing.
Component-Level Description:
IC201 and associated components filter the left channel signal emerging from
IC200. The purpose of these stages is to reduce the out-of-band noise energy
resulting from IC200’s noise-shaping filter and to translate the differential
output of IC200 into single-ended form. The components associated with
IC201 apply a 3 rd order low-pass filter to the differential signal from the D/A.
This filter does not induce significant overshoot of the processed audio, which
would otherwise waste modulation.
IC203B and associated components form a low-frequency servo amplifier to
remove residual DC from the signal. The 0.1Hz −3 dB frequency prevents tiltinduced
overshoot in the processed audio.