Digital Output - Arcam DiVA CD82 Service Manual

Analogue Output
Left channel:
IC400A and IC400B are cascaded 69kHz 2
Bessel filters. The output devices internal to both op-amps in
IC400 are "pulled down" to the negative supply rail to force
operation in class A (one output device is conducting at all times
and crossover distortion is eliminated).
IC402A is a DC servo with a very low cut off frequency, acting
to impose a non-zero voltage 'virtual earth' at the non-inverting
input of IC400B, thus eliminating the offsets caused by the pull-
down resistors and DC-coupling the output.
The right channel is the same as the left channel. IC401A & B
are used as the buffer and filter.
Microcontroller & Display Board
The system microcontroller IC100 serves the following functions:
!
Control of the mechanism & decoder on the CDM14
mechanism
!
Control of mute, attenuation and de-emphasis for the
DAC
!
Direct drive of the fluorescent display
!
Remote control decoding
!
Keyboard scanning
!
82/92DAC muting
The keyboard scanning works by connecting the keys to a resistor
ladder on an ADC input to the micro. Pressing a key presents a
unique voltage to this input, which the micro is pre-programmed
to interpret accordingly.
The remote control data contains a 'Customer Code' that
identifies this as an Arcam product. The diode network D100 to
D106 configures the micro to accept this code.
Remote Bus Carrier Filter & Demodulator
Remote control commands can be delivered over wire to SK500
for multi-room applications. Incoming signals are attenuated and
clipped by resistors and D500. L500 and C508 form a parallel
resonant circuit at approximately 37kHz. This demodulates the
incoming signal and the output is passed to IC501A where it is
'chopped', low pass filtered and fed to IC501B to provide the
RC5 output signal.

Digital Output

The decoder on the mechanism assembly generates an SPDIF
format digital output signal. This is passed to buffer IC500A.
IC500B through E are used in parallel to provide a transformer
less 75-ohm source impedance to a single phono socket SK501.
Optical digital output via IC502 is also tapped off the digital
output signal via IC500F.
nd
order low-pass