Kenwood TS-440S Serivce Manual page 9

TS-440S
CIRCUIT DESCRIPTIO N
2) AF notch circuit
R OH M
BX7I91— 851 8
123 10
BX719 I
R7 IOK R9 22K
OUT!
- S
C
5 10
+
0 iI t i
U
W
U
D27
D2 6
Fig . 5 NOTCH circui t
The hybrid ICI in the IF unit is an audio notch circuit .
Figure 5 shows its equivalent circuit . This circuit forms state-
variable band pass filter, also known as a bi-quad filter . Th e
notch frequency can be changed using the notch control vari -
able resistor . Since the circuit consists of the hybrid IC, sta -
ble attenuation characteristics can be obtained electrically an d
thermally . The range of variable notch frequencies is 400 H z
to 2600 Hz .
The notch frequency is determined by the following tw o
formulas .
1) f N
,,R6/27r (R1 +Notch VR)•R8•R10•C1 . C65 1
2) R6 . 1R12+R13)=R10•R11 2
If a variable resistor is used for resistor NOTCH VR, the notc h
frequency can be controlled according to formula 1) .
The notch frequency range is from 400 to 2600 Hz, and at-
tenuation is from 25 to 50 dB .
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