Loudspeaker Control And Avc; Dac; Headphone Branch; Interface Branch - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set

5.2.10 Loudspeaker control and AVC

(Automatic Volume Control)
The signal then passes through the loud-
speaker control stage. The control range
comprises 64 stages. In MSP 3411 each
channel has a second control stage for the
balance setting.
In addition, the MSP offers the facility of
measuring the level at the input. This is used
as the AVC function. This means that it is
possible to select different volumes for trans-
mitters during breaks for advertisements or
between different transmitters. Therefore, the
design does not provide for a programme lo-
cation related volume correction.
The actual value on the input determined by
the MSP is communicated to SDA 6000 via
2
the I C bus. In the operating software a pre-
cisely defined amplification is assigned via the
volume value. If the measured value deviates
from the required value, the volume is de-
creased or increased via the I
required value is reached.
VF level
transmitter
VF level
output
MSP
30-70ms
This means that various control constants are
used. Loud passages are toned down within
30 to 70 ms. An increase in soft passages on
the other hand occurs with a delay of about 10
s, to avoid an unwanted increase in volume
during the transmission. In addition, the AVC
can be switched off within the sound menu.
Document Q 2500
2
C bus until the
Break for
advertisements
ca 10s

5.2.11 DAC

A DAC is controlled with the signal set by the
digital controller. The analogue signal is out-
put for the right and left channels on pin
27/28. The signal is then fed via transistors Q
2081 and Q 2083, which are switched as an
impedance converter. Via the coupling capaci-
tors C 2082/84 the signal then arrives at W
1610, pins 1 and 2, and from there is fed to
the basic board on the two output stages.

5.2.12 Headphone branch

In the headphone branch there is an inde-
pendent volume setting, that can be changed
independently of the loudspeaker volume,
also in 64 stages.
The digital/analogue converted audio signals
for the headphones are output to pins 24/25.
The W 1494 audio Cinch sockets are supplied
with level by pins 36/37 of the MSP. In order
to deliver sufficient output level to these Cinch
sockets the Q 2500 chassis has in this branch
two amplifier stages, consisting of the opera-
tional amplifier I 2091C and D. The amplifiers
amplify the signal by a factor of 2. For the set-
ting "Sound via HiFi unit" the output level can
be set from 0 Vss to 3.5 Vss.
If "Sound via TV" is set, then there is a stan-
dard level on the Cinch sockets.

5.2.13 Interface branch

The audio level for the interface is set by the
operating software and cannot be changed.
The digital, analogue-converted VF signals for
the interface connection are applied to pins
33/34.

5.2.14 Deadline volume

During operation, a kind of awakening function
can be programmed into the Q 2500 chassis
as a deadline time. In addition, there is an
awakening tone, with an adjustable volume.
116 © Loewe ProCollege