Philips DVDR890 Service Manual page 55

EN 158 9. DVDR880-890 /0X1 Circuit-, IC Descriptions and List of Abbreviations
The sound processing is always done in stereo (that means
separate left- and right-channel). The complete selection of the
audio signal for recording is done by a HEF4052 [7501], which
is a dual four-to-one multiplexer. The Op-Amp on the output
[7504] is necessary for performance reasons and acts also as
a driver. The selected signals "ARADC" and "ALADC" are
directly fed to the Audio-ADC. The input lines for the selector
[7501] are coming either from MSP [7600] ("AFEL"/"AFER") or
cinch rear in 1 ("AIN1L"/"AIN1R") or cinch rear in 2 ("AIN2L"/
"AIN2R") or the cinch in front ("AINFL"/AINFR"). The [7501] is
controlled via "RSA1"- and "RSA2"-signals coming from the
MSP [7600]. The MSP acts as a port expander of the CC-µP.
As there can exist also a fifth input in case of DV-In is present
the corresponding analog audio signals from the DVIO-board
are firstly routed via extra cable and connector [1960] to the
MSP, which acts as a preselector between audio from internal
frontend or the DV-Input.
The signals from the audio DAC part ("ARDAC"/"ALDAC") are
directly routed to both cinch rear outputs, which are connected
in parallel. To avoid plops and any other audible noise on the
output there is a mute-stage implemented [7509], [7511] for
each channel. The activation is done via "AKILL"-line, which is
a combination of the "KILL" from CC-µP, "DAC_Mute" from
DAC-part and "IPFAIL" of the power-supply-unit. The circuit
around [6430], [6431], [7430] and [7404] generates this signal.
Additionally to analog audio the set is also equipped with a
digital output via cinch plug [1951]. The signal is generated on
the dig. board and routed via audio interface cable and
connector [1900] to the Ana-PCB. Here the "DAOUT"-line first
passes a 6-fold inverter [7580] being used as a driver and for
performance reasons (noise reduction, jitter, ...). Afterwards a
transformer [5580] is necessary to achieve the correct level
and also to have a ground isolated (floating) output before the
signal is fed via [3580] to cinch plug [1951]. The capacitors
POS [2580], [2582] & [2583] perform on the one side an AC-
coupling between connector- and set-ground. On the other side
they are necessary to keep radiation at a minimum for EMC
reasons.
9.4.3 Audio ADC/DAC
The conversion of analog audio signals from the record-
selector [7501] in the I/O ("ALADC"- & "ARADC") is done via
UDA1361TS [7005]. This IC can process input signals up to
2V by using an external resistor [3039], [3041] in series to
rms
the input pins. As the level from the DVIO-Board is only 1V
rms
a 6dB step can be performed by setting pin 7 of [7005] to 3,3V
via [7006] and "PWONSW"-line controlled by the CC-µP to use
the whole dynamic range of the ADC. All required clock
signals are generated on the dig. board and only the audio
data ("A_DAT"-line) are routed from Ana- to Dig.-PCB for
further processing.
The transformation of dig. audio back to the analog domain is
done by UDA1334BTS [7001]. All necessary clock signals are
coming from the dig. board and dig. audio data ("D_DATA0"-
line) are converted into analog signals, which are available at
pin 14 and pin 16 of [7001]. Afterwards an Op-Amp. [7002]
(line driver & level adaptation) and a low-pass-filter to increase
signal performance (noise, distortions,...). are passed. Then
both signals ("ALDAC" & "ARDAC") are directly routed to the
rear cinch output. The DAC has also a mute possibility, which
can be activated by setting pin 8 to 3,3V via [7003]. This mute
is controlled either by the dig. board ("D_IKLL"-line) or the
"IPFAIL"-signal from power-supply-unit.
In addition to that the DAC [7001] and the cinch outputs can be
killed (muted) in case of "digital silence" by the circuit around
[7008],[7009] and [7010], when no audio data are available
(e.g. "D_DATA0"-line zero)