An audio signal applied to VI is passed through the operational
amplifier 741, U2. After being amplified, the output signal V2 is
sampled and applied to a negative voltage doubler / rectifier circuit
composed of diodes CRI and CR2, with the capacitor C1. The resulting
negative voltage is used as a control voltage which is applied to the
door] 2N5485 FET Q1. Capacitor C2 and resistor R2 form a filter for
smoothing the voltage rectified audio control. The lFET is connected
between pin 2 of the MC3340P grounded by a resistor of 1 kohm.
Auto gain Control op-amp Circuit Diagram
As the voltage applied to the gate of FET] becomes more negative in
magnitude, the channel resistance of FET] increases causing lFET to
function as a voltage-controlled resistor. The MC3340P audio attenuator
is the heart of the MCO. It is capable of 13 dB of gain or almost - 80
dB of attenuation as a function of external resistor placed between Pin 2
and ground. An increase in resistance decreases the gain from the
MC3340P. The gain of the circuit is not entirely a linear function of
the external resistance, but such behavior is similar across much of the
gain / attenuation range. An input signal applied to the input of the
AGC will cause the gate volt age the proportion lFET become negative.
Accordingly, the JFET increases the resistance of the pin 2 to ground
the MC3340P causing a reduction in gain. In this way, the AGC output is
kept almost constant. source by next.gr
Datasheet file1: Click here to download LM741.pdf datasheet.Datasheet file2: Click here to download MC3340P.pdf datasheet.
Datasheet file3: Click here to download 2N5485.pdf datasheet.
Datasheet file4: Click here to download 1N270.pdf datasheet.
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