Microphone, line input unit

The mono microphone/line input unit is shown in Figure 3.28. It consists of two parts: a microphone input amplifier and a tone control circuit
. It is composed of four identical circuits and can be used for simultaneous
input of four microphones or electronic instruments (such as electronic keyboards, electric guitars, etc.). The channels are CHi~cr. Taking the first channel CHi as an example, a differential input two-stage amplifier
circuit is composed of VTc ~ VT3. The amplified signal is sent to the tone control circuit through the conversion switch SAlol. Microphone amplifiers have higher input
impedance, higher gain and signal-to-noise ratio. When there are electronic musical instruments and other line signals, they can be input from the line jack (LINE)
. At this time, the input signal is directly converted by SAioi without amplification. The above two input signals
can pass through the tone control circuit through the control of the change-over switch SAioz, or can be directly sent to the next level circuit without going through the tone circuit. Iclol
, RPi01, RP102 and RC network form a feedback tone control circuit . RP103 is the channel attenuation potentiometer, used to control
the size of the output signal. Wei, 04A and RP104B are double synchronized potentiometers, used to adjust the ratio of left and right channel signal strength
to produce the effect of moving the sound image direction left and right. Rlzo is the isolation resistor between output and input.