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5.0 Electric Circuits
5.1 LINE AMPLIFIER
The line amplifier comprises transistor 0101 with
associated components, and is identified as LINE
AMPLIFIER on the circuit diagram. The amplifier has
a flat frequency response extending from 30-20 000
Hz, and has a voltage amplification of 4.5 times. The
capacitor C102 serves as decoupling for high fre-
quency signals. The output is connected to the top of
LINE LEVEL potentiometer R2 via C104.
5.2 MICROPHONE AMPLIFIER
The microphone amplifier comprises transistors 0102
and 0103 and is identified in the main circuit dia-
gram, as MICROPHONE AMPLIFIER. The frequency
response is flat rom 30-20 000 Hz, and the amplifica-
tion is 150 times. Negative feedback from the collec-
tor of Q103 to the emitter of Q102 is applied through
the components C109, R113 and R111. The feedback
is stabilizing and frequency independent. Capacitor
C106 serves as a decoupling for high frequency sig-
nals. The signal from Q103 is fed to the MIC LEVEL
potentiometer R5 via C112.
5.3 BUFFER AMPLIFER
The amplifier comprises transistor 0208 with asso-
ciated components and is identified on the main cir-
cuit diagram, as BUFFER AMPLIFIER.
The signals from MIC LEVEL and LINE LEVEL poten-
tiometers are mixed and fed to transistor Q208 via
C126. The buffer amplifier has a flat frequency res-
ponse and an amplification of 5.5 times.
5.4 EQUALIZING AMPLIFIER
The equalizing amplifier consists of transistors 0201
0202 and Q203 with associated components. A fre-
quency depending network connected from emitter
of 0203 to emitter of Q201 establishes the appropri-
ate frequency response for recording and playback.
5.4.1 Equalizing Network for Recording
A simplified diagram for the equalizing network in
record mode is shown in fig.5.1. The emitter feedback
R204
C 213
20 6J_C 2 Ol_C 2 0 4
I.
1207
Tr
Fig. 5.1 Record equalizing network.
reduces the amplification approximately 30 dB in the
intermediate frequency range. The frequency res-
ponse in this frequency range is determined by capa-
citor C207, while C208 and R213 determine the respon-
se in the lower part of the frequency range. The series
resonance circuit L201, C204, R208, R209 and C211
are the frequency determining components in the
upper frequency range. The equalizing switch is
linked with the speed selector, and correct equaliz-
ing for the various speeds is automatically establish-
ed when the speed is changed. The components
mentioned above refer to the tape speed 71/2 ips. The
speed correction for 33/4 ips is obtained by means
of C205. At 17/8 ips, correct equalizing is obtained by
means of C206. The resulting record equalizing curve
is shown in fig. 5.2a. See chapter 8.1 on modifications
for Low Noise tape.
dB
20
15
10
S
0
5-
10
50
100
200
SOO
1000
2202
MO 101200 20000
10112
20
50
100
200
500
1000
2020
5020 10000 20020 50000
Fig. 5.2 a Record equalizing curves.
'...... '`.. , ,
,, .......
44
..,.,............. ....
1 2/ •
--",..........
..............
"--
71 a
.... s
50000
10
15
20
25
10112
20
Fig. 5.2 b Playback equalizing curves.
Fig. 5.3 Playback equalizing network.
.3
25
20
15
10
5
S
re
71 /2
24
0 201
0203
1 ,
1
1r
PI,
71 / 2
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