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Referring to the equivalent circuit in Fig. 3 and the principle circuit in Fig. 4, we explain the operation of the circuit.
The input signal is applied in between K313 and earth and then to the PIN 8 via the C301. The Q1 and Q2?2 serve as
differential amplifier, which works to connect the signal given with the single power supply (from the previous stage)
with the amplifier operated on the split power supply. The Q3, D1 and D2 form constant voltage circuit. The signal,
which is differencial-amplified in the Q1, is supplied to the base of Q4 via the PIN7
. The D6 ~ D8, connected to the
collector of Q4, give an appropriate bias to the next stage and also supply thereto the balanced signal with the earth
positioned at the center. The Q11 is NPN transistor. These PNP and NPN transistors form complementary circuit.
Therefore, the upper half of waveform is amplified at the Q401 via the PIN 2 and the lower half amplified at the Q403
via the PIN 13 , which then appear in the K313 as output waveform. Since the DC voltage of K313 is of OV, it is not
needed to use the coupling capacitor conventionally employed in the SEPP type amplifier. (The name of OCL is derived
from this fact.) The Q15 works to filter the ripple of +B if the capacitor is inserted to the PIN 4 . The Q11 and Q13
form current limitter. If an abnormal current runs in the Q401 and Q403, DC voltage increases in the R313 and R315
and reaches the base of Q10 and Q13 via the PIN 1 and 12 , causing the signal to be grounded. The minimum current
required for operating this protection circuit can be adjusted by the values of the R309 and R311. The R305 is a
resistor to determine the negative feedback amount. With the R305 lessened, the nagative feedback amount decreases,
thus increasing the gain of the maplifier. To the PIN 6 and 7 is connected the capacitor for preventing the oscillation.
The OCL amplifier is an ideal amplifier. from the following points; Its low frequency response characteristic is superior in
particular because of the absence of the coupling capacitor, and flat reproduction is assured up to as low as 10Hz in the
case of main amplifier alone. In addition, negative feedback is sufficiently applied due to the IC driver to remarkably
lessen the distortion.
2. EQUALIZER AMPLIFIER
OUTPUT
!
Fig. 5 Equivalent Circuit
Fig. 6 Equalizer Amplifier
Explained here is the operation of this circuit. The internal equivalent circuit of the IC201 is of directcoupled 3-stage
amplifier. The first stage Q1 serves as grounded emitter circuit and the input signal, coming via the K202, is amplified at
the base of QI and then appears in the collector. In order to increase the collector load of Qi the second stage Q2 and
third stage Q3 are made an equivalent circuit with Darlington connection, thus the input impedance at the second stage
is increased.
The last stage Q3 serves as grounded emitter circuit and obtains the output from the collector. The bias is supplied from
the emitter (PIN 5) of Q3 to the base (PIN 2) of QI via the R205. (DC negative feedback type.)
agin,
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