Audio AGC amplifier circuit

Audio AGC can keep track, monitor audio preamplifier output signal level when the input signal increases, AGC circuit automatically reduces the gain of the amplifier; when the
Audio AGC amplifier circuit - schematic

input signal is reduced, AGC circuit automatically increases the gain of the amplifier, so that an a/D signal is maintained at an optimum level, but also make the clipping is minimized. As shown in FIG audio amplifying circuit AGC, dynamic range greater than this amplifier 50dB, the output waveform distortion is very small, and has started fast, slow decay advantages. Circuit input 40 ~ 20mV and 0 ~ 1.2V adjustable output level, a single power supply, current consumption less than 1mA (5V voltage). VT2, VT4 P-channel JEFT, it R2, R3, R4 (R10, R11, R12) constituting the equivalent resistor divider input circuit access. When the input level is lower than 40mV (peak to peak), the input evenly between R2 and R3, R4 distribution, A1 output amplitude is not large enough to make a positive peak detector VT2 conduction. The gate of the JFET pulled + 5V, pinch off the channel and it produces a very very high resistance from drain to source. When the input voltage peak to peak higher than 40mV, VTl turned A1 in positive peak output, lowers the junction-type FET gate-to-source voltage. Channel resistance and to reduce the attenuation of the input signal, in order to keep Al peak to peak output voltage of about 1.2V.

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