This opamp combination you propose is very new to me.

The circuit is very common:

https://www.maximintegrated.com/en/design/technical-documents/app-notes/3/3201.html

They use an opamp as a comparator which is okay for slow circuits, and convenient because they're using a quad opamp. All open collector comparators will swing rail to rail, but most opamps won't. The one in the circuit will.

 

@dl324 I simulated it and it is getting the result right...for a few seconds and it crashes. Its my simulator not very well made for PWM. I have to find another simulator for these more complicated circuits. I have LTspice installed but im not that familiar with it, even after a couple of tutorial, its still ... weird. Ill try un-weird it soon. :] But in 2 seconds of feedback I could glimpse the right effect in my sim. I think if i build it, (with 3x 741 since i dont have any other models) it will be ok. Yah, interesting project ! Thank you.
And mister @Audioguru again, think of a project for me, from where i can taste more of the gain problems. As you already exemplify and describe it in this discussion here, was super helpful so far. Lets do something more practical or useful as a circuit with some gain in it.
We are reaching new heights of understanding very soon ! (mostly me)

 

I think if i build it, (with 3x 741 since i dont have any other models) it will be ok.

Do yourself a favor and buy some opamps that don't have as many limitations. The design was ground breaking when it was first introduced (it was the first opamp that didn't require external compensation) and is still a fine opamp (if you know how to use it), but there are many opamps that are more novice friendly.

 

I have been in electronics for 50 years and have used many opamps. But I have never seen or used a lousy old 741 opamp.

An opamp as a non-inverting voltage amplifier has a feedback resistor and a resistor to ground. The ratio of the resistors plus the number one, calculates the voltage gain at DC or any frequency in the bandwidth. The inverting opamp has a feedback resistor and an input resistor.

 

Many of the older book experiments and basic circuits are based on the LM741. So what would suggest as a replacement for it for those learning about Op Amps?

 

@dl324 Those binding posts (color and the end stripes) and Pozidrive screws scream HP or one of their spin offs.

 

Do yourself a favor and buy some opamps that don't have as many limitations. The design was ground breaking when it was first introduced (it was the first opamp that didn't require external compensation) and is still a fine opamp (if you know how to use it), but there are many opamps that are more novice friendly.

I understand you completely and I agree with you completely. But see it as I see it. At least at this point in my first steps into opamps. For me opamp does not (yet) have any special value or significance. I dont really tried all its opamp modes/circuits, to understand its real value. I do not see it yet, especially from a few experiments and simulations. So for me is fine whatever i use, and more important is the chip to work and behave properly. Don't get me wrong, when I will finally get what is most important to use for (and that is a subjective matter, depending on the needs and knowledge of everyone) then I will be choosy, and trust me i am very choosy when i know what i want. For the moment this old and inefficient opamp uA741 that i already have, i treat it as a work horse, probably in your eyes is more like a toy opamp because its limitations. But I want to live a little its limitations, that I don't feel them yet as I am still learning and experimenting. Again, trust me, I will scream so loud when I will see its limitations, you will make the brownies. :] , For me, it is a general opamp at this point, as i said work horse ..better, experiment horse. It's also what i have in stock and i do with what i have. I will listen to you both, and buy new ones soon enough, but until then i will push the limits of this one as i can. And I agree there are probably more easy, the other opamp versions, to use and understand, but this one I already started to crack and is not that hard now especially with your help. In general lines, i use it when I need one of its modes, but to remember them, i need to actually build them and get a bit of experience with it. Its a type of memory, when I do this, and is working for me (specifically) very well in decurs of time.
Thank you so much for your understanding and help. Being with me on this road, is more important to me that the actual teachings. Doing it alone is very frustrating, i am doing it alone for a long time, and its very shitty experience (pardon my french).

 

Many of the older book experiments and basic circuits are based on the LM741. So what would suggest as a replacement for it for those learning about Op Amps?

There are many New models of opamps these days, more specialized on specific functions, from what I read so far. The generic ones that my friends here are suggesting to me already and I took notes to buy them in the near future, is this one:
LM137 - https://forum.allaboutcircuits.com/attachments/lm137_lt-pdf.218008/
or LM318, LM358
LM324 for DC and low-frequency AC circuits,
TL082 for AC projects involving audio or higher frequencies.
single op-amp chips include the LM741, CA3130, and TL081.
dual op-amp chips include the LM1458 and TL082.
As mister Chips said: "For starters, many applications call for single supply, rail-to-rail operation. "
Basically, look in the datasheet for rail-to-rail part, and see if is included in your opamp
Also for single supply voltage, and that means from 0 to +Vs. But if im not mistaken (i imagine) they >>ALL<< work for dual supply, -Vs 0V +Vs. Single supply is more convenient and easy to use, especially for a beginner, and it was exactly how i was thinking a week ago, but is limited functionality (in my opinion, now that i got some experience with the double power supply these days, and im happy i took the challenge).
- Coincidentally, I got this page from google (i searched for "opamp general models") that is from this very website and I think is pretty good: https://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/operational-amplifier-models/ After looking around a bit i discovered that this page is in fact a page from a pdf, that held many interesting informations, and is very easy to read. Super easy. https://www.allaboutcircuits.com/assets/pdf/semiconductors.pdf ; And from this link i just posted here: "While the 741 is now considered outdated in terms of performance, it is still a favorite among hobbyists for its simplicity and fault tolerance (short-circuit protection on the output, for instance). Personal experience abusing many 741 op-amps has led me to the conclusion that it is a hard chip to kill ." - I didnt know before reading this page, why it remained so popular, but now I know why.
Now, this is interesting:

So you can make an opamp from your components as well. That is an interesting project in itself. Especially if you want a quick and dirty high output current.

 

Instead of 741, can you find the following?

LM324
LM358
TL081
TL082

All of these are "old" designs but they should be readily available and useful for experimentation.

 

Many of the older book experiments and basic circuits are based on the LM741. So what would suggest as a replacement for it for those learning about Op Amps?

The LM741 is still a useful opamp; as long as you understand its limitations. Some people seem to have a bias against parts from the 70's and 80's. The transistors and diodes I use most often are also from that era and they're still useful.

Tektronix seemed to favor LM741 in their equipment from the 70's/80's because it was a good opamp at that time. I was going through some parts and prototypes I had from that time frame and I used a uA741 to generate the programming voltage for an EPROM programmer. I could have used a more expensive opamp (LM308, LM318, LF356), but I chose to use the general purpose device.

I bought some rail to rail opamps a year or two ago to see what all the fuss was about. They're still in the original packaging. In that time, I've breadboarded dozens of opamp circuits and all have used LM358 or LM741 (I used the 741's because #12 gave me some pulls he had no use for and I wanted to test them). The rail to rail opamps were around a dollar each; most circuits I design work fine with a 25 cent (in qty 100) LM358. I have "more modern" opamps, but haven't built any circuits that needed them.

 

@dl324 Those binding posts (color and the end stripes) and Pozidrive screws scream HP or one of their spin offs.

Guilty. That was back when HP meant Have Pride to employees. It's been about 40 years since I worked there and they're not the same company now. Of course, I can say the same thing about the company I retired from. They've all lost their way...

 

LM318,

One of the things most designers will do is not over specify parts for a circuit. It drives up expense unnecessarily and it makes them look like they're clueless.

LM318 is a specialized opamp (high slew rate). Using it in a generic circuit like the ones you've been working on would be overkill; like using a sledge hammer on a thumb tack.

EDIT: The LM318 still has similar input and output voltage constraints that others have been denigrating the 741 over. Opamps from that era were more likely to use +/- 15V supplies. They were never intended to operate from a single 5V supply.

LM358 was probably the first designed to operate from a single 5V supply. Because it was designed to take that in to consideration, the input voltage range includes ground. The output isn't as capable as the earlier opamp designs because the designers took advantage of the fact that it was designed to operate from a single supply.

 

This is a completely parallel issue i have from my original project with the ldr led driven stuff. Again, a reminder, i am not an electronist, but im a hobbyist, im an artist, so you'll have to forgive my way of talking and explaining. Im doing my best with the limited knowledge i have about some things, but im not Very limited.
In my previous post, mister @Audioguru again suggested me to use an opamp and I knew about its existence but not at all familiar with it. So here is my way of understanding it. It became my quest from that moment. Again, a parallel quest with my main objective.
I did my best to enunciate my problem here in this artpage.
If not that well understandable, do point it out.
Thank you.
View attachment 216463

Title: Understanding Basic Electronics, 1st Ed.
Publisher: The American Radio Relay League
ISBN: 0-87259-398-3

You will find anything you wish to do in electronics much easier if you read this book.

 

For the moment this old and inefficient opamp uA741 that i already have, i treat it as a work horse, probably in your eyes is more like a toy opamp because its limitations.

I'd never call the uA741 inefficient. I'll accept that it's an old design, but that doesn't make it useless. It still performs as it was designed to. I wish I had been the one to design it. Saying that it's bad because it's old and has limitations is like a construction worker using brad nails for framing and complaining that they don't work. It's a poor workman who blames his tools. You need to know what to use and when to use it.

But I want to live a little its limitations, that I don't feel them yet as I am still learning and experimenting.

You need to understand that all opamps aren't equal. The circuit I posted was intended to be used with a single supply opamp. The opamp being used is has rail to rail outputs, but that circuit can be built with LM358 and LM393; I've done it. There are going to be some limitations on the output voltage swing, but it can be done.

EDIT: Generating a PWM signal doesn't require that the triangle wave output swing rail to rail.

You'll also have an easier time if you buy that inexpensive oscilloscope I mentioned. It will be easier to troubleshoot opamp circuits because the main use for opamps is linear and a DVM isn't very useful for observing how things are (or aren't) functioning.

 

Here's some history on the early opamps:

https://www.tech-tins.co.uk/details_page.php?id=tt21&catid=4

EDIT: more history.
Signetics:

 

40 years was different. I did a Boy Scout's Explorer's post back in 1972 at an HP site that manufactured GC's where we laid out a a digital clock using the old tape method in team of 3 or 4. Our group had the 2nd put together and the first working clock. The HP67 was relatively new during that time frame. I ended up maintaining HP stuff, primarily X-Y recorders at work.

 

...I'd never call the uA741 inefficient. I'll accept that it's an old design, but that doesn't make it useless. ...
...You need to understand that all opamps aren't equal. ...
...EDIT: Generating a PWM signal doesn't require that the triangle wave output swing rail to rail....

You'll also have an easier time if you buy that inexpensive oscilloscope I mentioned. It will be easier to troubleshoot opamp circuits because the main use for opamps is linear and a DVM isn't very useful for observing how things are (or aren't) functioning.

- I agree with everything you say there. Its exactly the same how I think also. So we are on the same frequency here. Which is very good. This way you know a person.

- I did take action already with the osciloscope, you know Im listening to smart and interesting characters as yourself and mister @Audioguru again . The action consists as I am in contact with the seller on Alibaba website, and i wait his response, because i want to be sure (from his mouth) that i will receive some parts they show there (the acrylic case , already soldered, and P6100 probe that i can see it in every profesional osciloscope, so it must be important, for sure it looks important, but also looks expensive $6.14). Click on the second picture from those 3. https://www.aliexpress.com/item/32778225027.html I want to be sure they are not only for show and have a surprise when i get it(im refering to the case and already soldered). The probe is clearly separate. I wonder if i can find it cheaper that $6.14, already used is also an alternative for me. As I said, its a big thing to me, so im precocious. Being poor as f.., is another reason to be precocious as well. Im an artist so its written on my forehead. :] Haha. Capitalism, right?

 

Be careful with what you are ordering.
US$6.46 is for hook cables, not P6100 probe.
DSO138 and P6100 probe is US$19.00
Plastic case is US$7.04

 

What you are buying is a kit that ONLY has the SMDs soldered onto the board. You will have to solder the rest of it and put it all together. The case is a typical chinese jigsaw puzzle with NO instructions on how to put it together. I built one for my son and took the case apart several times before I got all the buttons and switches to semi work. It ain't perfect by any means but it does kinda work. Just be very very careful not to drop it. In fact, if you are careful with it, you might not want to put the case on it. FWIW The vendor typically has no idea of what it is, just it's profit margin for him. All he is doing is selling widgets. It's up to you to know what the widget does.
EDIT: Also, there will be NO documentation, specifications, or user instructions. NADA! You can find some reviews and documentation if you get lucky googling for them.

 

The action consists as I am in contact with the seller on Alibaba website, and i wait his response, because i want to be sure (from his mouth) that i will receive some parts they show there (the acrylic case , already soldered, and P6100 probe that i can see it in every profesional osciloscope, so it must be important, for sure it looks important, but also looks expensive $6.14). Click on the second picture from those 3.

I bought this one for $20. It was soldered and came with a cable with alligator clips. I had to assemble the case, which had no instructions and it took me a few tries. I didn't need a scope probe because I already have dozens.

https://www.aliexpress.com/item/32778225027.html?spm=a2g0s.9042311.0.0.27424c4d10ccFy