Automatic Gain Control Pre-Amplifier Circuit Diagram

Automatic Gain Control Pre Amplifier Circuit


Automatic Gain Control PreAmplifier Circuit Diagram

The preamp circuit uses an easily obtained 741 op amp set for an internal gain about 200.

Automatic Gain Control Pre-Amplifier Circuit Diagram

PARTS LIST
R1 100kΩ
R2 470Ω
R3 10kΩ
R4 10kΩ
R5 560kΩ
R6 100kΩ
R7 10kΩ
R8 10kΩ PRESET
R9 100kΩ
C1 1µF 16V
C2 1µF 16V
C3 10µF 16V
C4 1µF 16V
C5 0.1µF (104)
C6 10µF 16V
C7 0.22µF (224)
D1 1N4148
D2 1N4148
Q1 BF245
IC1 LM741

A portion of the op amp’s output signal is rectified by the 1N4148 diodes, then filtered and fed to the gate of the FET input shunting circuit. As the output rises, more and more input shunting takes place. That is, more of the input signal is bypassed, effectively keeping the output level constant.

BF245 FET

BF245

This preamp circuit offers a 100:1 limiting action. The input level can change over a 100:1 ratio with little or no effect on the output level.

741-8-pin-ic-configurations-top-view

741 PIN CONFIGURATION

The output output level itself can be set from less than unity all the way up to nearly the gain of the amplifier, making the circuit usable in other applications as well.

Automatic Gain Control PreAmp Circuit Automatic Gain Control PreAmplifier Circuit Automatic Gain Control Pre Amplifier Circuit Diagram


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8 comments on “Automatic Gain Control Pre-Amplifier Circuit Diagram
  1. PRUDENCIO G. PERITOS JR. says:

    hello , can you suggest me the replacement or subtitute the FET BF 245,,,no available this kind of transistor in our place,Please reply me soon,
    Hoping your kind consideration regarding this matter,

    Thanks,

  2. Vox says:

    Can the electrolytic caps be MMLC instead?

  3. Inese says:

    Hei!

    Is there a way how to calculate all the necessary element values? Or it’s done just by trying? Thanks!

  4. rohan says:

    Please send me your Automatic Gain Control PreAmplifier Circuit Diagram.Thanks.

  5. rahul singh says:

    very good

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