Why do we need Amplifiers? How to build a simple one? LM 741

February 14th, 2006

You have some output source (for example an analog sensor) where the voltage is very low, just few mV (millivolts), and you would like to measure the output with your ADC (Analog to Digital converter) and with the results do some calculations with your MCU (Microcontroller) or some other device. The values the ADC gives you are all almost the same because its bit resolution is too small to show you any differences between the different states of the sensor.

One solution to our problem would be to get a better ADC with a greater bit resolution but that automatically means you would have to make a better PCB (Printed Circuit Board) because of the noise problems and etc. Seems like an expensive solution. However, there is a simpler and cheaper solution. We can make a voltage amplifier. It is a simpler solution, you can trust me.

To realize this simple project you will need just a few parts; two resistors, two 9V batteries, one famous and popular operational amplifier IC (Integrated Circuit a.k.a. chip), LM741, a breadboard and some wire to connect the parts on the breadboard.

LM741 is an operational amplifier. “An operational amplifier or op-amp is a very high-gain amplifier which has two inputs, one inverting (−) and one non-inverting (+). The output voltage is the difference between the + and − inputs, multiplied by the open-loop gain.” – Definition by Wikipedia. It is a very popular and famous IC used in a wide range of applications. It can be used for voltage, current and other amplifications. In our case it is a non-inverting voltage amplifier.

We amplify a signal by the following rule y=G*x (this is only the case for the linear amplifiers, not logarithmic or any other amplifier). y is our output signal, G is the gain and x is our input signal. For an example you have a signal that is between 2 – 5 mV and we want to get an output signal eleven times greater than the input one, 22 – 55 mV. So our gain should be eleven. Right, we need a formula to calculate the values of external components to get our gain. Every amplifier has its own formula, given by the manufacturer, to calculate the gain. For the LM741 the gain formula is the: G=1+R2/R1, see the schematic on figure 1.

LM741 Schematic Operational Amplifier
Figure 1.

As we want a gain of eleven one solution would be to use R2 = 10kΩ and R1 = 1kΩ. When we put these values into our formula G = 1 + (10 000/1 000) we get a gain of eleven.

In one of my projects I needed a gain of 5.7 so I used R2 = 47kΩ and R1 = 10kΩ. Here are the results on my HAMEG oscilloscope, figure 2. The bottom signal is from the signal generator, on the scale of one volt. It was not supposed to be a square signal in case you already think “what a bad signal” . The upper signal is the output signal from our circuit, on the scale of five volts.

The highest point at the bottom signal had amplitude of 0.8V. At the same point just on the upper signal the amplitude was 4.56V. This is one of the ways to test your amplifier; by changing the signal types (sinusoid, triangle, square and many other), voltage amplitudes and frequencies.

LM741 and Oscilloscope
Figure 2.

If you do not know how to build this circuit, you can see a picture of it on my breadboard, figure 3. In case you do not have a negative voltage generator you can use two 9V batteries. Connect them as on figure 4, colors match the colors on the breadboard.

LM741 Operational Amplifier circuit breadboard
Figure 3.

Negative Voltage power suply
Figure 4.

We encourage you to download the datasheet of your manufacturer but on figure 5 you can see the pin out for the DIP version of LM741.

Operational Amplifiers Pins LM741
Figure 5.

I hope you understood this simple practical project of building a small voltage amplifier. If you want to know more about operational amplifiers you can go to our book section and download the book “Op Amps for Everyone Design Guide”, Texas Instruments. In case you did not feel free to ask me, comment or mail me.

Entry Filed under: Electronics, DIY

39 Comments Add your own

1. Man | | March 13th, 2006 at 10:02 pm

Thanks keep this way!
2. Rick Hoffstatter | | March 22nd, 2006 at 4:44 pm

I’m trying to set up this LM741 Op amp.
How do I hook up the input and output?
I’ve got a +/-1.5V that I want to be atleast
+/-5V. I think I have everything put together
but I just don’t know how to hook up my
(-) leads. Do they go to the ground?
3. Ian Oliver | | April 2nd, 2006 at 12:08 am

I need to build an amplifier for . Will this amp work?

Hi, I’m tring to buid a non-inverting amplifier for a 12vdc supply with 1.5 to 2.2vdc on Vin +. I’m using a 6.2K & 2.2K (on Vref to ground) resistor combination to pump up the voltage. I’m having trouble coming up with an Op-amp to do the job. If you could please recommend one & a wiring diagram.
Thanks for any help Ted Elliott.

could this curcuit work as a mic amp?

6. danny | | June 14th, 2006 at 9:34 am

awesome,but can some one help me with this projet can you show more pictures.can you explain step by step……please
7. kevin | | September 19th, 2006 at 12:17 am

i really need the basic of all amps, i really dont need anything for it just an amp. probally 3v… anyone help!!!!!!
8. Mandar | | November 3rd, 2006 at 5:30 am

Nicely explainedapplication of non-inverting amlifier,explain more application of 741 e.g.audio amp,preamp,postamp etc.
9. Kevin Minton | | November 14th, 2006 at 11:52 pm

Can you run your output from the amp into another amp as your non-inverting. using it to amplify your signal by a large amount. That way one could use smaller resistors, and save costs.
10. ayman mounir | | November 22nd, 2006 at 4:07 pm

thanks to u for this information,……….
i want to know the design of operational amplifier
thanks
11. shane | | December 8th, 2006 at 3:01 pm

haha sweet
12. edmarlo | | January 2nd, 2007 at 10:30 pm

very good…
13. adele | | January 8th, 2007 at 4:58 pm

can anyone kindly enlightme on how non-inverting op-amp with two resistor operate
thanks
14. Chris Habib | | January 9th, 2007 at 12:54 pm

I NEED UR HELP URGENTLY! hehe
plz can u give me a schematic for an amplifier with the following specifications:
input 5 mv (microphone)
gain 1000V/V
bandwidth up to 20 Khz

thx a lot! i really need it a.s.a.p… plz reply !
15. robert wells | | January 11th, 2007 at 9:25 pm

i need a 750 watt amp will this one work? if not do you know how to build a cheep amp that will work please send me a e-mail thankz
16. Anand | | January 21st, 2007 at 7:12 pm

I want to increase frequency from 50Hz to 100Hz. with out chaning Voltage.Voltage range(1-1.5V). Can I choose LM741 for this purpose. If it it possible Just explain me how is it possile? If u can please help me. Thanks
17. Koniel IDEI | | January 31st, 2007 at 12:19 am

I am building an OP amp using a LM741 to substitute a LM748 using a 11.5V supply for a codan 7515 SSB radio.I dont have the pin out diagram for the SIP version of the ICs. plis help
18. ramy | | February 7th, 2007 at 3:23 am

i wanna amplify a mic output voltage af 1mv p-p to 2.5 p-p, i used inverting amp but failed when simulating in topspice, is it not practical or what?
19. linn | | February 10th, 2007 at 1:42 pm

Thanks for the usefull information.It is really help me in my project.
20. Abdul Wahab | | February 14th, 2007 at 3:05 pm

Its a very good method i appriciate u and ur gathering
21. Sunita | | March 22nd, 2007 at 11:42 am

Thanks,I got some idea.
22. subhashree | | March 22nd, 2007 at 12:00 pm

actually,how can we design a 3-stage amplifier?
23. Milo | | March 26th, 2007 at 4:52 am

Sheesh! Did you open a can of worms, or what? You give people a simple idea, and they want you to give them the world.
24. Chuck | | March 31st, 2007 at 5:42 pm

Actually the limit of the 741 has to do with the product of gain and bandwidth. under most conditions you don’t want to use the 741 for anything faster than about 1khz, at a gain of 10 or so. Another limit is that 741s rarely work with power of less than +/- 9 volts as supplies. There is however good news, there ARE opamps that get better results. As for a non inverting amp, you really should use at least 3 resistors.

more shortly.

Chuck
25. Ken | | April 4th, 2007 at 11:03 pm

Do you have info on how to set up a flyback. The open loop, close loop things confuses me. Do you know of any books?

K
26. Najib Lugar | | April 5th, 2007 at 10:16 am

How to build a (Raised cosine filter) ?
If you know please contact me, my mail adr is najibmail@gmail.com.

regards

Najib Lugar
27. pawan | | April 10th, 2007 at 11:18 am

hi, i want to amplifi the 2mv signal to +12v is it possible with the above circuit??. if it is not then could u explain the other circuit which can do the same job.
28. ahmed | | April 23rd, 2007 at 1:22 pm

Hi all, i want to amplifi 3V signal to 15V with 15VDC source shall i use the op-amp without any resistances?? or it won`t give me the desired value?
i`m an undergradute mechanical enginner, i don`t know too much in electricity
if anyone want to help plz contact me, my mail is seiko_1327@hotmail.com
Thx
29. Naveen | | May 2nd, 2007 at 1:13 pm

I want to amplify microphone output(around 5mV) with a band width of 20KHz. how can acheive it using ua741(opamp) with low noise output.
plz its urgent.
30. kajan | | May 3rd, 2007 at 9:18 am

hello hello , i am building/built a 3 stage amplifier using a LM741 for stage1. i got a serious problem because my gain for the second stage is 500 instead of 10. got any tips on how to reduce my gain from the second stage. thank you. regards Kajan Lakhan
31. Esko | | May 3rd, 2007 at 5:31 pm

Hello,
the LM741 is not really a good choice for an opamp, because it is old and slow. The TL072 is a much better choice and is even cheaper.
You can see on your oscilloscope that the amplified signal has a higer rise time.
Comment 24. Chuck already mentioned most arguments.

mfg Esko
32. Saber Motasadi Zarandi | | May 28th, 2007 at 11:27 am

Tnx
i Have been save all of them of web page s form ths site
33. ganesh | | June 14th, 2007 at 2:58 am

thanks it gives idea
34. ankit | | July 25th, 2007 at 9:40 am

i have an mp3 player(it only has an earphone jack) which i want to hook up to big speakers(havnt decided yet but i was thinking of some really loud speakers). how can i build an amplifier for this. can i use the one above.
35. lacsters | | July 27th, 2007 at 4:13 am

Can you use this amplifier to amplify mV output span pressure sensor to V? Any cons behind it… say noise etc

I guess… is this a precision amplifier?
36. JIGAR M BHATT | | August 2nd, 2007 at 4:59 pm

I M THE STUDENT OF BSC PHYSICS. I WANT TO MAKE NORMAL PROJECT FOR SEE HOW TRANSISTOR WORK AS AN AMPLIFIER.
I HAVE REFERED SOME REFRENCES BUT I WANT SIMPLE PRACTICALY CIRCUITWITH COMPONETS VALUES WHICH GAIN IS 10.

THANKS
JIGAR.
37. jayalakshmi | | August 30th, 2007 at 2:55 am

I want to amplify the voltage level from lillivolt range to volt range. Can I choose Ic 741for this puspose .Just explain how it is possible .If u can help me .Thanku
38. shivu | | September 25th, 2007 at 9:11 am

awsome,, it’s very sweet n shortly xplaind…. tnks!
39. RAMU | | October 1st, 2007 at 12:59 pm

very easy to understand