Revox B261 Serviceanleitung Seite 38

STIJDtrR
IIEVOX
8261 SA
SECTION
3/3
FIVE STAGE
LIMITER/AMPLIFIER
FRO[,1 NF-AMPLI
FtER
1.726.730
AGC-AMPLI.
FREOUENCY
DISCRIMINATOR
TO RF-AIVIPLIFIER
PCB
1.7
26.1
30
TO SIGNAL STRENGTH
METER
TO CENTER
TUNING METER
3.3 IF
AMPLIFIER
L.726.740
From
the balanced mixer stage, the IF signa] is taken to the
IF amplifier
through a passive phase-linear
fil-ter comprisj.ng
8 tunable circuits
with a bandwidth of 130 kHz (+65
kHz,
response down 3 dB, on
RF
amplifier
PCB
1.726.73dt.
The IF signal is amplified
and limj,ted by five integrated
differential
anplifiers ICI through IC4 and IC2 on L.'126.750.
The signal is rectified after the fj-rst stage, amplified in
Q3
and used as the
AGC
signal for controlling the first
RF
amplifier stage.
Through a rectifj.er and a
summing
amplifier, the first four IF
amplifiers supply the information for the sig4a1 strength meter
and for controll-ing the station
search.
The
signal is decoupled after the fourth IF stage and taken to
the frequency discriminator.
The latter supplies the contro.L
signal for the center tuning instrument and the station
search.
3.4
DEMODULATOR
PCB
L.126.750
MPX ITO
STEREO DECODER PCB)
FROM IF-AMPLI
F\EB1l2614A
MPX,M (TO STEBEO DECODER PC8)
From the last IF stage the signal rs taken through a driver
stage to the digital
FM
demodulator which is alternately
controll-ed directly and through a 68 ns delay line. A filter
network develops the
mean
from the pulse sequence of the
demodul-ator circuit in the form of a demodulated
MPX
signal.
After a phase-linear 100 kHz low-pass, the
MPX
signal is taken
through a di-fferential amplifj.er to four 95 kHz Cauer
1ow-passes
with terrninal,s at 99, l0l-, 114, and
L]
6 kKz (L3 to L6). The
MPX
signal alternateLy
reaches the stereo decoder directly
and
indirectly through the muting ci-rcuit
(with terminatrng
ampli-f
iers ).