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DIY Hobby projects, diagram, schematic

Automatic Gain Control Pre-Amplifier Circuit Diagram

electronicecircuits, November 8, 2010August 15, 2023
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
R1100kΩ
R2470Ω
R310kΩ
R410kΩ
R5560kΩ
R6100kΩ
R710kΩ
R810kΩ PRESET
R9100kΩ
C11µF 16V
C21µF 16V
C310µF 16V
C41µF 16V
C50.1µF (104)
C610µF 16V
C70.22µF (224)
D11N4148
D21N4148
Q1BF245
IC1LM741

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 CircuitAutomatic Gain Control PreAmplifier CircuitAutomatic Gain Control Pre Amplifier Circuit Diagram

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Electronic Circuits PreAmplifier Circuits

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Comments (13)

  1. lal jani basha says:
    November 10, 2010 at 5:20 pm

    tanks for sending

    Reply
  2. rahul singh says:
    November 18, 2011 at 7:28 pm

    very good

    Reply
  3. rohan says:
    November 10, 2012 at 6:53 pm

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

    Reply
  4. somjedh says:
    January 2, 2013 at 4:21 am

    good

    Reply
  5. Inese says:
    April 25, 2013 at 6:36 pm

    Hei!

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

    Reply
  6. Vox says:
    July 9, 2013 at 9:39 pm

    Can the electrolytic caps be MMLC instead?

    Reply
  7. PRUDENCIO G. PERITOS JR. says:
    October 24, 2013 at 12:33 pm

    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,

    Reply
  8. waqas ali says:
    October 26, 2013 at 6:53 pm

    AWEGFAWER

    Reply
  9. Pingback: Automatic Gain Control PreAmplifier Circuit Diagram | Electronic Circuits
  10. Lorelee says:
    November 7, 2014 at 8:41 am

    We have tried the circuit, but it does not function as AGC. It could produce sound , maybe its pre-amp circuit works fine. what could be the problem?
    Thanks a lot

    Reply
  11. مهندس حسین عظیمی says:
    November 25, 2014 at 1:09 am

    ok very good

    Reply
  12. muzammil says:
    April 8, 2015 at 12:55 pm

    what does this means what is the exact specification on the these two capacitor 0.22µF (224)
    and 0.1µF (104).

    Reply
  13. Henry Dheel says:
    May 2, 2015 at 1:22 pm

    there is a book named FORST MIMMS mini note books
    THE OPAMP 741 1458 AND OTHERS
    THERE IS A PAGE ON CALCULATEING THE GAIN

    P.S.radio shack sold the book long ago

    Reply

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