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40
100
200
400 600
1K
2K
4K
6K 8K 10K
20K
40
100
~200
400600
1K
2K
4K
6K 8K 10K
20K
Fig. 20
Characteristic graph of noise level
Fig. 2)
a g
___=
Noise
level
nN
°o
50
100
500
1k
2k
5k
10k
20k
——=_
Frequency
(Hz)
Fig. 22
Function of Each Block
Refer to the block diagram.
Buffer Amplifier
This is the emitter follower (2SC1335).
It is designed to reduce the influence to the first half stage of
the system, and at the same
time, make the filter circuit (consisting of the ANRS
control circuit and
non-linear control elements) operate correctly.
Non-Linear Control Elements and ANRS Control Circuit
As non-linear control elements, transistors X302 and X402, as well as 2SC1335, are used. Asa DC VBE
is applied to the circuit between the transistors B and E, the impedance ZcE between C and E is varied
by the impressed voltage VBE from © up 10 Q. This theory is also applied to the AGC circuit.
The high-pass filter is made up of the ANRS
control circuit and the said variable impedance elements
(Fig. 23). This high-pass filter has such frequency characteristics that they vary according to the value of
the impressed voltage VBE, as indicated in Fig. 24.
Note that the high-pass filter has a loss of about
25 dB.
During the recording operation, a signal passes through this circuit, by which the intermediate and high
frequencies are amplified.
During the playback operation, the high-pass filter is inserted in the feedback
loop of NF, and as a result, it serves as a low-pass filter having the reversed frequency characteristics.
Control Amplifier
The control amplifier is a circuit to generate the VBE
which is impressed to the transistors, that is,
non-linear control elements.
In this circuit, the signal voltage is amplified by IC (IC302 and 402), and a
DC control voltage is produced by the voltage doubler rectification of diodes, D301, 302, 401, and 402.
This DC control voltage is varied by semi-fixed volume controls, R315 and 415. The rectifier circuit has
constant
circuits,
C316,
416,
R317
and
417
so
that
the
control
voltage
has a proper
transient
characteristic.
In addition, bias traps, L301, 401, C317 and 417, are provided to keep the ANRS circuit
free from adverse effects caused by bias leaks.
As part of the control amplifier, it has a circuit, from which a DC bias is applied to transistors of variable
impedance elements.
This bias current can be varied by semi-fixed resistors, R320 and 420.
If Zce is
too great, the output of the high-pass filter exceeds 10 dB, and therefore, by adjusting the bias current,
the output is kept at 10 dB.
—11—-
CD-1667, 1667U
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