Multi-channel microphone input amplifier

It is a four-channel microphone input hybrid amplifier composed of BA328. It has the advantages of low noise and fewer external components
. oBA328 is a two-channel preamplifier integrated circuit composed of two amplifiers. It
is composed of two BA328 and has Mixing amplifier with four microphone inputs. It can insert four high-impedance microphones at the same time.
After the signals picked up by the microphones are amplified by their respective amplifiers, they pass through the coupling capacitor clt~C14 and get a mixed signal output at both ends of R13. In order
to facilitate the connection of the output mixed signal to the microphone input jack of the amplifier, the mixed amplifier intentionally reduces
the gain of the amplifier. The output signal level of each channel is realized by adjusting the control potentiometer RPi ~ Gang) 4 of. Since the gain of this
amplifier is low, it works stably. When using it, just use a shielded wire to directly connect the mixed output signal to
the microphone input jack of the amplifier. If the mixed signal of this output is required to be connected to the line input jack, the gain of the amplifier
should be adjusted to 40dB. At this time, just change the feedback resistor Rz, wind, R6 and Rs to a resistance of 15 kfl.