Headphone Amplifier - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set
On the Dolby Digital Module the two surround
channels are muted via transistors Q 8/Q 4/5
and Q 6/7. If a data error is detected on the
Dolby Digital Module during digital sound sig-
nal processing, pin 30 on I 01 outputs H level.
Via the two transistors Q 9 and Q 10 the mute
function is then activated. For the mute func-
tion the Dolby Digital Module represents both
input and output.
As you can see from the mute circuit, some
sounds have an output line, as, for example,
for the LFE channel Q1552/56, two transistors
are used. This measure improves the mute
behaviour and the error rate of these stages.

5.2.16 Headphone amplifier

As in previous models the front panel of the
device has a connector for headphones. As
for the loudspeaker branch the signals are
Document Q 2500
also generated in the MSP 3411. As already
described, the loudspeaker control for the
headphone control is also implemented in it.
These signals are output in pulse width modu-
lated form on pins 24 and 26 of the MSP and
integrated with external RC components into
an VF signal at up to 1.2 Vss. They are fed
respectively to an amplifier stage, consisting
of 2 transistors Q 1441/46 and Q 1461/66.
This stage amplifies them to 9 Vss and out-
puts them via a decoupling through C 1448/68
to the headphones socket and pin 2/4 on pin
connector W 1431 for the HF transmitter.
The headphones volume can be controlled in
63 stages and the setting displayed on the
screen.
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