How to Make a Simple Active Low Pass Filter Using IC 741

In electronics, filter circuits are basically employed for restricting the passage of a certain frequency range while allowing some other band of frequency into the further stages of the circuit.

Types of Low Pass Filters

Primarily there are three types of frequency filters that are used for the above mentioned operations.

These are: Low pass filter, high pass filter and the band pass filter.
As the name suggests, a low pass filter circuit will allow all frequencies below a certain set frequency range.

A high pass filter circuit will allow only the frequencies which are higher than the preferred set range of frequency while a band pass filter will allow only an intermediate band of frequencies to flow to the next stage, inhibiting all frequencies which may be outside this set range of oscillations.

Filters are generally made with two types of configurations, the active type and the passive type.
Passive type filter are less efficient and involve complicated inductor and capacitor networks, making the unit bulky and undesirable.

However these will not require any power requirement for itself to operate, a benefit too small to be considered really useful.

Contrary to this active type of filters are very efficient, can be optimized to the point and are less complicated in terms of component count and calculations.

In this article we are discussing a very simple circuit of a low pass filter, which was requested by one of our avid readers Mr.Bourgeoisie.

Looking at the circuit diagram we can see a very easy configuration consisting of a single opamp as the main active component.
The resistors and the capacitors are discretely dimensioned for a 50 Hz cut OFF, meaning no frequency above 50 Hz will be allowed to pass through the circuit into the output.

Circuit Diagram

single opamp low pass filter circuit

For technical explanation of the circuit you may refer to the data provided here.

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Swagatam said…
May be this circuit will help:
Swagatam said…
IC 741 is the only basic code, and all shopkeepers will understand this code.
swagatam sir i wanted to know that in this low pass filter there is 1 audio in and 1 audio out , but in speakers there are 2 one is positive and the other is ground i wanted to know that where is the other one
Swagatam said…
Hi Sumukha, the above circuit is not meant for direct connection with the speaker, it is to be connected in between the music source and the power amplifier....the power amp output needs to be with the speakers.
sir can we use 12v instead of 9v ?
Swagatam said…
yes it can be used
akshay jha said…
sir i want to make 2.1 circuit board so i want to know that i can use this circuit as subwoofer circuit or not for good sount and i have 444ic amplifire circuit is it suitable or not
Swagatam said…
akshay, don't use the above circuit because there are even better circuits than this, you can find plenty if you Google it.
tony blazer said…
is there any prob if i use 12v for my circuit.
Swagatam said…
can be used...12-0-12V
Sumant Kulkarni said…
hey, i am little confused. we know that the cut off frequency equation as f = 1/(2pi*sqrt(R1C1R2C2)) , so if we use this then we will end up with 3.38 Hz as cut off... so could you help out.?
Sumant Kulkarni said…
hey, we know that fc = 1/(2PI*sqrt(R1R2C1C2)) ,so by the given values cut off freq will end up with 3.38Hz , i m confused.. could you help me out pl..?
Swagatam said…
I am not so sure about the formula because I have not researched it yet....however the C in the formula could be in Farads. so make sure you have converted the value in Farad first and then inserted in the formula.
Sumant Kulkarni said…
yes yes, that is obvious rite.!! it will be in farads and in formula what would be inserted is also in farads. anyway, if you could tel me more briefly after your research i will be obliged :)
Thanks for the reply
Saeed Ansar said…
sir i want to design an active filter that remove 3rd harmonic produced by CFL loads and 3rd harmonic frequency is 150hz.Can you give me the circuit??
Swagatam said…
Saeed, you will need a notch-filter for that, you can Google it.
muhamad nazreen said…
sir,i have a project that ask me to reduce harmonic content on power system by using an active filter. 240V and 50Hz frequency. can u help me to design or to choose which type of active filter i should use for this project?
thanks in advance.
Swagatam said…
Muhamad, please Google "power saver circuit" I think that's what you may be looking for.
Michael Mouton said…
What component values do I need to chance to get it to cut off at 100Hz?
Swag said…
you could probably refer to this article and calculate the parameters easily:

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