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I have made low pass filter both on Breadboard and in Proteus.Both of them have different problems. I have kept voltage gain at "3". In breadboard,voice output in the earphone is lower than input.In input I have a microphone When I blow air by mouth, It give me rough voice hearing by earphone. In case of simulation in Proteus,When I applied above 333 Hz freq, output in speaker is still beep. I cant understanding what is this happening.. Please help me...I am beginner.R1(1)-sinwave input),R1-150,R3-500,C1-1uF,C2-470,LS2-speaker(output)

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    \$\begingroup\$ Even if your filter works, it is a very weak filter and will only reduce the 333Hz tone by a small amount. \$\endgroup\$ – JRE Dec 25 '16 at 13:14
  • \$\begingroup\$ You have no power rail attached to the unspecified triangular shaped thing. Pretty much restricts help to guesswork. \$\endgroup\$ – Andy aka Dec 25 '16 at 19:44
  • \$\begingroup\$ This is LM 741 IC. \$\endgroup\$ – Umesh Dec 26 '16 at 3:58
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1) You are using a single supply. Analyze the circuit for positive inputs. This requires negative outputs. Where will the - voltage come from?

2) You do not specify your op amp. Most op amps are completely incapable of driving 8 ohms, which the usual nominal speaker impedance. You need a power stage for the output - subject, of course, to fixing part 1).

3) Using 500 ohms for feedback and 150 ohms input is too low. For instance, you need to check to see if your AC source is happy driving 150 ohms. A good function generator will drive 50 ohms, but many sources aren't happy doing that. Use 10k and 30k. This will also let you use a smaller capacitor.

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  • \$\begingroup\$ IC I used is LM 741. \$\endgroup\$ – Umesh Dec 26 '16 at 3:59

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