Recording level display circuit

(4) Only the manual recording level control function is provided. When the circuit is in the recording state, the LM3915N is used to display the recording level
. As shown in Figure 3-180,
    in the recording and playback circuit of Figure 3-17, the recording and playback preamplifier circuit is composed of IC] and related RC networks . In the playback
equalization circuit, there are playback equalization networks for three different tapes: ordinary tape (NOr), chrome tape (Cr02) and metal (Met) tape
, which are controlled by the switch.
    IC2a ​​and other components form a playback voltage amplification circuit. , to adapt to the input level requirements of the power amplifier circuit.
    IC2b and related networks form a recording equalization network. For ordinary tapes, R17, RisCl1 and C12 form a low-frequency compensation
network, and high-frequency compensation consists of R19, ‰, Cl3, and q4. For chrome tapes and metal tapes, only high-frequency compensation is required, C15 -,C16
and R2l form the high-frequency compensation of the chromium belt, and C17.CIS and Biao form the high-frequency compensation network of the metal belt .
    RP3 is a manual recording level adjustment potentiometer.
    The high-frequency transformer T and VTi, Vtz form a push-pull high-frequency bias magnetic oscillation circuit, and the oscillation frequency is 90kHz;. On the one hand, the bias
magnetic oscillator provides erasure bias current for the erasure head, and on the other hand, it supplies the recording and playback magnetic head with recording and playback bias current.
In order to ensure the stability of the bias oscillation frequency, the power supply of the bias oscillation circuit uses an LC filter. In the bias oscillation
circuit, there are also selector switches for ordinary belts, chrome belts, and metal belts to provide different oscillation currents.