Audio Demodulator (Diagram B6) - Philips EM5E AA Service Manual

9.12 Audio (Diagram B6, A6 & A7)
9.12.1 Introduction
All EM5E sets contain one of ITT's Multi-standard Sound
Processing (MSP) ICs for sound decoding. The diversity arises
because each member of the MSP-family handles its own set
of sound standards:
• MSP34x1:
• MSP34x2:
Both versions also handle NICAM.
The MSP IC takes care of the main FM sound decoding. AM
decoding for the L system is done by the HIP. The demodulated
L sound is then again source selected and processed in the
MSP. The reason for this is the bad AM detection performance
of the MSP. However, in case of NICAM L, it is handled by the
MSP.
All MSP versions contain digital audio processing, used for the
basic left/right stereo sound, such as bass, treble, balance,
incredible sound and spatial.
In addition to that, both versions are capable of Dolby
processing:
The MSP34x1can perform 'Virtual Dolby' processing (a Dolby
approved sound mode for surround sound reproduction with
left/right speakers only).
7651
47
MAIN IF
MONO-IN
HIP
50
ANA_INI+
44/45
EXT1 L/R SC1-IN
MICRONAS
41/42
EXT2 L/R SC2-IN
MSP3411
38/39
FRONT L/R SC3-IN
35/36
EXT3 L/R SC4-IN
Figure 9-20 Virtual Dolby processing
The MSP34x2 can perform 'Dolby ProLogic' processing (left,
right and (mono) surround).
7651
47
MAIN IF
MONO-IN DACA_L/R
HIP
50
ANA_IN1+
DACM_L/R
DACM_SUB
DACM_L/R
MICRONAS
MSP3412G
DACM_C
44/45
EXT1 L/R SC1-IN
D_CTR_I/O_0
41/42
EXT2 L/R
SC2-IN
38/39
FRONT L/R SC3-IN
35/36
EXT3 L/R
SC4-IN
SC2-OUT
SC1-OUT
Figure 9-21 Dolby Pro Logic processing
Circuit Descriptions and Abbreviation List
Virtual Dolby decoding.
Dolby ProLogic decoding.
7770
17/18
DACA_L/R
7700
20/21
DACM_L/R
Constant Level
CL L/R
SC2-OUT
25/26
7652
74HC4053
1/3
SCART 2
4/15
2/5
16
SEL_IN_2
SCART 1 / decoder out
TUNER L/R
SC1-OUT
28/29
CL 16532044_028.eps
7770
17/18
24
7702
23
7652
7700
74HC4053
20/21
7702
22
"Set is center"
7653
Constant Level
Variable Level
2 times
CL L/R
74HC4053
25/26
SEL_IN_2
7652
SCART 2
74HC4053
SCART 1 / decoder out
TUNER L/R
28/29
CL 16532044_029.eps
The following amplifier configurations are possible:
• Virtual Dolby, L/R, 2 x 15 W (88XX-series and 8957-series
with extra digital input).
• 3D Surround, L/R, Centre, Subwoofer, 4 x 15 W (95XX-
series).
9.12.2 Inputs / Outputs
Both versions can cover four stereo inputs and one AM (mono)
input. This means in practice: three SCART inputs, one side
input, and one AM (mono) input.
Both versions have the following outputs: SCART1 (CVBS/
decoder out), SCART2 (record select/WYSIWYR out) and
headphone.
9.12.3 Source Selection
The constant level output to SCART2 is connected via a so-
called 'Régimbeau' switch (IC7652) (see also Figure 9-13).
This switch is needed to prevent acoustic feedback ('Larsen'
effect). This effect is caused, when EXT2 is chosen as input
signal, and the output of SCART2 is selected. This means that
the main picture is also EXT2, which will cause the 'Larsen'
effect.
To prevent this, the record select must be switched to 'Tuner'.
This is especially important when decoders are used, behind a
'transparent' VCR connected to EXT2.
HEADPHONE
CINCH
To get a constant level output if the Tuner is selected, the
SCART1 output ('Tuner' at any time) has to be fed back to the
input selector and selected as input for the MSP (SCART1
L/R
MAIN
input).
The MSP34XX has a separate headphone output, so sound
control can be done separate from the speakers.
9.12.4 Audio Decoding
At the input, a choice can be made between two IF-signals; SIF
and SIFM.
140501
The selected signal is fed to the AGC. After this, an ADC
converts the IF-signal to digital.
Two demodulation channels can process this digital signal. The
first one is able to handle FM and NICAM signals. The second
one can handle FM and AM signals.
Each channel contains a mixer to shift the incoming signal in
the frequency domain. This shift is determined by the value of
a DCO.
After the down-mix, the signal is fed, via a filter, to a
HEADPHONE
discriminator. From here the AM, FM or NICAM demodulation
Surround cinch
or Phone plug
can be performed.
Both channels contain an 'automatic carrier mute' function,
SUB
WOOFER
which automatically mutes the output of the analogue section
when no carrier is detected.
MAIN
After demodulation, the FM-signals are subjected to a de-
emphasis operation. After that, the matrix of the stereo system
is applied.
CENTER
9.12.5 Audio Processing
The sound processing in EM5E is completely done by the
MSP:
• Volume control is done by the user via the SOUND menu.
• Tone control in 'Stereo' sets is done via the BASS/TREBLE
control, in 'Virtual Dolby' sets via the 5-band equaliser.
140501
• Headphone control, the MSP has a separate Headphone
output so separate sound control is possible.
Automatic Volume Levelling (AVL)
One of the features of the MSP-family is Automatic Volume
Limiting (AVL). If used, it limits the big volume differences in the
EM5E 9. EN 119