Project using OP-Amp 741

[mojat]

Hai friends, I need a small signal amplifier using three 741 op-amp. I am a beginner in electronics and it will be helpful for me if some one will come up with a circuit and the functional details. Thank you all.

 

[Nigel Goodwin]

Your request is far too vague, you need to give much more exact details - for a start what is it connecting to, what gain does it need, and what are the source and load impedances.

 

[mojat]

Sorry, I will give u the details.

 

[audioguru]

(He must ask his teacher about the details)

 

[i_build_stuff]

Hai friends, I need a small signal amplifier using three 741 op-amp. I am a beginner in electronics and it will be helpful for me if some one will come up with a circuit and the functional details. Thank you all.

Here you go.

**broken link removed**

 

[bananasiong]

Or you want a 3 state amplifier?

 

[dknguyen]

That sounds like homework...

 

[bananasiong]

If it is homework, it should be 3 state amplifier..

 

[audioguru]

I think it is a class-D amplifier. But the old 741 opamp is way too slow and doesn't have enough power output.
His schematic is missing a few things:

 

[i_build_stuff]

I think it is a class-D amplifier. But the old 741 opamp is way too slow and doesn't have enough power output.
His schematic is missing a few things

It'll work.

 

[Nigel Goodwin]

It'll work.

But do what? - it's going to be really crap! - as Audioguru says a 741 is far too slow for class-D, and also outputs hardly any power. A completely pointless exercise!.

 

[i_build_stuff]

As a learning excersise, it would be a good circuit to expriment with. It demonstrates a lot of interesting effects without being complicated, and it can be made useful with a few very simple changes.

As a (plagiarized) homework assignment, on the other hand, it's probably giving some professor a good laugh right now...

 

[audioguru]

As a learning excersise, it would be a good circuit to experiment with.

Not when it is using an lousy old slow opamp instead of a high speed comparator.
Many class-D audio amps have a switching frequency of about 384kHz. The lousy old 741 opamp has trouble above only 9kHz. An ordinary TL07x audio opamp goes up to 100kHz.

 

[mojat]

Beginner

Hai, you are right. I am beginner in electronics not studying in a college but learning all by myself out of interest in electronics. So you people are my teachers and many things do I ask do appear as home work and I need your help for that. I am attatching a circuit I intend to test on a bread board and I need to know the values of R and C so that I can make it work properly. Thanks all of you.

 

[audioguru]

Hi Mojat,
A circuit needs to have specification requirements:
1) How much gain?
2) What is the cutoff frequency of this lowpass filter?
3) Is the source DC-coupled to 0V?
4) What are the supply voltages?

Your first opamp doesn't have DC negative feedback and has a DC gain of about 200,000. So it will amplify its input offset voltage of up to 10mV which might cause its output to be saturated. Then it won't work.
Do a simple filtered amplifier like this instead:

 

[mojat]

Thanks Guru, but I asked about the values of R and C. Can you give me the values or the way it should be calculated. As I told you this is only a test circuit I am doing to learn, the supply is +/-12v and I dont know about the gain and cut-off frequency.

 

[audioguru]

If you want to learn about electronics then you should read about it.
Go to www.google.com and look for Opamp Tutorial or something like that.

Learn about how the ratio of two resistors set the gain (amount of amplification) of an opamp.

Learn about what is a lowpass filter and its cutoff frequency. Then learn how the values of its R and C determine the cutoff frequency.