Akai VS-2EGN - Page 28

2) Frequency doubling circuit
The signal at the emitter of TR55 is in phase with the
input signal but a 180° reversed signal appears at the
collector. Twice the original frequency is obtained by
3) 1.07 MHz Bell Filter
05 06 07 08 LO
Lb
Fig. 7-18 Frequency doubling circuit
half-wave rectifying and mixing the signals at D23 and
D24 respectively. (Refer to Fig. 7-18)
W243 SLT Mz,
09
29
10
dB
:
-20
0B
L
1O7MHz
Since the signal was subjected to the anti-bell filter
operation during recording, it will be directed to pass
through the bell filter with the complementary charac-
teristic during the playback. That is, this is DE-EM-
PHASIS to PRE-EMPHASIS in recording. Its charac-
teristic is shown in Fig. 7-19. Here, the amplitude of
frequencies that had been emphasized are restored to the
original condition and the response becomes uniform re-
lative to the center frequency.
4) Limiter
The signal equalized by the PB EQ has become uneven in
its amplitude due to noise, drop-out, uneven recording/
playback, etc., ie., it is amplitude modulated. In order
to keep the amplitude constant, amplitude limiting is
performed by the limiter. Then, the signal is directed
to the next MPX.
Fig. 7-19 1.07 MHz Bell Filter
5) BPF
-3dB
(|
i
1
|
!
1
|
|
1
|
1
i
>t LBMHz 2.3MHz 2.8MHz
Fig. 7-20 Characteristics of Band Pass Filter
The frequency of the 1.07 MHz CHROMA signal is
doubled (2.14 MHz) by the first doubling circuit. Un-
wanted signals are removed by the 2.14 MHz BPF.
Service Manual VS-2EGN
25